Anti-GBM Disease
Anti-GBM disease is a small-vessel vasculitis caused by circulating autoantibodies directed against the alpha-3 chain of type IV collagen in glomerular and alveolar basement membranes, leading to rapidly progressive glomerulonephritis and, when pulmonary involvement occurs (Goodpasture syndrome), diffuse alveolar hemorrhage.
Anti-GBM Disease (Anti-Glomerular Basement Membrane Disease)
Anti-GBM disease is a rare, organ-specific autoimmune disorder characterised by the production of circulating autoantibodies (IgG) directed against the non-collagenous (NC1) domain of the α3 chain of type IV collagen in the glomerular basement membrane (GBM) [1][2]. The name breaks down simply:
- Anti = against
- GBM = glomerular basement membrane (the filtration barrier in the kidney)
This autoantibody binding triggers a potent inflammatory response that manifests as:
- Rapidly progressive glomerulonephritis (RPGN) — the kidney component
- ± Pulmonary haemorrhage — because the same α3(IV) collagen is found in the alveolar basement membrane
When both kidneys and lungs are involved, the condition is historically called Goodpasture's syndrome (named after Ernest Goodpasture, who described it in 1919 during the influenza pandemic) [2]. Strictly speaking:
| Term | Meaning |
|---|---|
| Anti-GBM disease | The overarching disease entity (autoantibodies against GBM) |
| Goodpasture's syndrome | Anti-GBM disease with co-existent pulmonary involvement (pulmonary-renal syndrome) |
| Goodpasture antigen | The NC1 domain of α3(IV) collagen — the specific target antigen |
"Anti-GBM disease is also known as Goodpasture's syndrome or disease when there is co-existent pulmonary disease" [2]
Key Distinction
Many students confuse the nomenclature. Anti-GBM disease is the disease. Goodpasture's syndrome is the clinical phenotype with lung + kidney involvement. Not all anti-GBM disease patients have lung disease — some have renal-limited disease only, especially older patients ( > 50 years).
2. Epidemiology
- Rare disease: incidence approximately 1.64 per million per year [2]
- Accounts for < 5% of all glomerulonephritis but 15–20% of all RPGN [2]
- Accounts for ~1–5% of all crescentic glomerulonephritis cases globally
- More common in Caucasian populations; relatively less common but still reported in East Asian (including Hong Kong Chinese) populations
- Bimodal age distribution:
- Overall slight male predominance (~60% male)
"Younger more likely to be full-blown Goodpasture's but older patients ( > 50y) more likely to have isolated GN" [2]
- Anti-GBM disease is rare in Hong Kong but is a recognised cause of RPGN
- In Hong Kong, the most common causes of RPGN are ANCA-associated vasculitis and IgA nephropathy with crescents, but anti-GBM disease must always be considered given its rapidly fulminant course
- HLA associations (HLA-DRB1*1501) are present across ethnic groups including Chinese populations
3. Risk Factors
Understanding risk factors requires understanding the pathogenesis: the Goodpasture antigen is normally "hidden" within the collagen IV network. Disease occurs when (1) there is genetic susceptibility allowing an autoimmune response, and (2) an inciting event "exposes" the antigen.
| Factor | Mechanism |
|---|---|
| HLA-DRB1*1501 / HLA-DRB1*1502 | Strong genetic association; these HLA class II alleles present the Goodpasture antigen peptide to CD4+ T cells more effectively, breaking tolerance [2] |
| HLA-DR4 | Weaker positive association |
| HLA-DR1, HLA-DR7 | Protective — associated with lower risk (dominant protection) |
| Complement deficiencies | Rare association |
"Genetic susceptibility: a/w HLA-DRB1*1501/1502" [2]
Most patients have no identifiable trigger [2]. However, when triggers are identified:
| Trigger | Mechanism of Action |
|---|---|
| Cigarette smoking | Pulmonary epithelial injury → exposes alveolar basement membrane α3(IV) collagen → immune system "sees" the antigen. Smoking is the single most important risk factor for lung involvement — virtually all patients with pulmonary haemorrhage are current smokers or have recent smoke exposure [2] |
| Pulmonary infections (e.g., influenza, COVID-19) | Alveolar inflammation damages alveolar basement membrane → antigen exposure |
| Hydrocarbon inhalation (organic solvents, glues) | Direct pulmonary epithelial toxicity |
| Lithotripsy / urological procedures | May disrupt renal basement membrane |
| Cocaine inhalation | Pulmonary injury |
| COVID-19 | Recent case reports describe anti-GBM disease triggered post-SARS-CoV-2 infection |
"Those with lung involvement more commonly a/w underlying pulmonary injury, eg. smoking, infection ('exposes' the pulmonary Ag)" [2]
Why Does Smoking Cause Lung Haemorrhage?
The Goodpasture antigen (α3 chain of collagen IV) exists in both the GBM and the alveolar basement membrane. However, in the lung, this antigen is normally sequestered — hidden within the intact alveolar capillary membrane. Smoking (or infection) damages the pulmonary endothelium, exposing the antigen to circulating anti-GBM antibodies. This is why:
- Non-smokers with anti-GBM disease tend to have renal-limited disease
- Smokers present with pulmonary haemorrhage (Goodpasture's syndrome)
- The key clinical advice: all patients with anti-GBM disease must stop smoking immediately
- Post-transplant anti-GBM disease can occur in 5–10% of renal transplant recipients with underlying Alport syndrome [2]
- Why? Alport syndrome = mutations in COL4A3/A4/A5 genes → abnormal or absent α3/α4/α5(IV) collagen chains. When these patients receive a normal kidney transplant, they are exposed to normal α3(IV) collagen for the first time. Their immune system has never been tolerised to this antigen → de novo anti-GBM antibody production against the transplanted kidney
- This is called post-transplant anti-GBM nephritis (a form of alloimmune anti-GBM disease)
4. Anatomy and Function: The Glomerular Basement Membrane
To understand anti-GBM disease, you must understand the structure the antibodies attack.
The glomerular filtration barrier consists of three layers (from capillary lumen to Bowman's space):
Capillary Lumen
↓
1. Fenestrated endothelium (70-100 nm pores)
↓
2. Glomerular Basement Membrane (GBM) — the TARGET
↓
3. Podocyte foot processes with slit diaphragms
↓
Bowman's Space (→ proximal tubule)The GBM is a specialised extracellular matrix composed of:
- Type IV collagen (the structural scaffold) — forms a network of triple-helical protomers
- Laminin (cell adhesion)
- Nidogen/entactin (cross-linking)
- Heparan sulphate proteoglycans (charge barrier — negative charge repels albumin, which is also negatively charged)
Type IV collagen has 6 α chains (α1 through α6). The mature GBM contains:
- α3(IV), α4(IV), and α5(IV) collagen chains assembled into a heterotrimer: α3α4α5(IV)
The NC1 (non-collagenous 1) domain is the globular domain at the C-terminal end of each collagen IV chain. The α3(IV) NC1 domain is the Goodpasture antigen — the specific epitope targeted by anti-GBM antibodies.
The α3(IV) collagen chain is found in:
| Location | Clinical Consequence |
|---|---|
| Glomerular basement membrane (kidney) | RPGN, crescentic glomerulonephritis |
| Alveolar basement membrane (lung) | Pulmonary haemorrhage |
| Choroid plexus, cochlea, eye (Bruch's membrane) | Rarely clinically affected (antigen normally sequestered; blood-tissue barriers intact) |
Why is the kidney always affected but the lung only sometimes?
- In the kidney, the GBM antigen is constitutively exposed to the circulation (the glomerular capillary is fenestrated → antibodies have direct access)
- In the lung, the alveolar basement membrane is protected by intact endothelium → antibodies cannot access the antigen unless the endothelium is damaged (by smoking, infection, etc.)
Similar architecture to the GBM but thinner. It contains the same α3α4α5(IV) collagen network. The alveolar-capillary membrane normally acts as a barrier preventing antibody access to the basement membrane collagen. Injury (smoking, infection, fluid overload, high FiO₂) disrupts this barrier.
5. Etiology and Pathophysiology
- Target: NC1 domain of α3 chain of type IV collagen (the Goodpasture antigen)
- Antibody class: Predominantly IgG (IgG1 and IgG3 subclasses → potent complement activation), rarely IgA or IgM
- Specificity: The antibodies bind to two specific epitopes (EA and EB) on the α3(IV) NC1 domain. These epitopes are normally cryptic — hidden within the hexameric structure of collagen IV and only become accessible when the quaternary structure is disrupted
Detailed mechanistic narrative:
-
Initiation — Loss of tolerance: In genetically susceptible individuals (HLA-DRB1*1501), an unknown trigger (possibly molecular mimicry, infection, or environmental exposure) breaks immune tolerance to the α3(IV) NC1 domain. CD4+ T helper cells recognise the Goodpasture antigen presented by HLA class II molecules → activate autoreactive B cells
-
Autoantibody production: B cells differentiate into plasma cells producing high-affinity IgG anti-GBM antibodies. These antibodies are transiently produced — the autoimmune response is typically self-limited (lasting weeks to months), which is a key feature distinguishing anti-GBM disease from other autoimmune conditions. This has therapeutic implications (plasma exchange can remove the antibodies, and they may not recur)
-
Antibody binding: Anti-GBM antibodies bind uniformly and continuously along the entire length of the GBM → this creates the characteristic linear IgG staining pattern on immunofluorescence [1][2][3]. This is in contrast to:
- Granular pattern (immune complex deposition, e.g., lupus, IgAN)
- Negative/pauci-immune pattern (ANCA vasculitis)
-
Complement activation: IgG1/IgG3 binding activates the classical complement pathway → C3a/C5a (anaphylatoxins) recruit neutrophils and monocytes; C5b-9 (membrane attack complex) causes direct GBM injury
-
Inflammatory cell recruitment: Neutrophils and macrophages accumulate in the glomerular capillaries → release reactive oxygen species, proteases, and cytokines → further GBM damage
-
GBM breaks and crescent formation: Severe GBM damage creates gaps ("breaks") → plasma proteins (including fibrinogen/fibrin) and inflammatory cells leak into Bowman's space → "massive movement of plasma product into Bowman's space → subsequent massive influx of MQs/T cells, release of proinflammatory cytokines → formation of cellular crescent" [1][4]
-
Crescent evolution:
-
Progression to ESRD: Without treatment, > 90% progress to end-stage renal disease or death [2]
"Pathogenesis: transient production of circulating autoAb vs GBM (IgG) against the Goodpasture Ag — NC1 domain of α-3 chain of collagen IV" [2]
"Autoreactive Ab → potent inflammatory response → crescent formation with glomerular destruction" [2]
- Anti-GBM antibodies also bind the alveolar basement membrane (same α3(IV) collagen)
- Pulmonary capillaritis → damage to alveolar capillaries → red blood cells leak into the alveolar spaces → diffuse alveolar haemorrhage (DAH)
- Haemoglobin in the alveoli is taken up by alveolar macrophages → haemosiderin-laden macrophages (siderophages)
- Chronic/recurrent pulmonary haemorrhage → iron-deficiency anaemia (iron is sequestered in the lungs)
- ANCA may be present in 10–50% of anti-GBM patients [2]
- Usually MPO-ANCA (p-ANCA) positive
- Clinical significance: dual-positive patients may have a slightly better prognosis because ANCA-associated vasculitis tends to respond better to immunosuppression and has a more relapsing-remitting course
- These patients may have features of both anti-GBM disease and ANCA vasculitis
- It is hypothesised that ANCA-mediated vasculitis may precede and trigger anti-GBM disease by disrupting the GBM and exposing the Goodpasture antigen
"ANCA: may be present in 10-50% anti-GBM pt, indicates better response to Tx" [2]
6. Classification
Anti-GBM disease is classified within the framework of:
RPGN is classified based on immunofluorescence (IF) staining pattern [1][3][4][5]:
| Type | IF Pattern | Cause | Serology |
|---|---|---|---|
| Type I (Linear IF) | Linear IgG along GBM | Anti-GBM disease | Anti-GBM antibody +ve |
| Type II (Granular IF) | Granular immune complex deposits | Immune complex-mediated RPGN (SLE, IgAN, PSGN) | ANA, anti-dsDNA, complement ↓ |
| Type III (Negative IF) | Negative/pauci-immune | ANCA-associated vasculitis (GPA, MPA, EGPA) | ANCA +ve (most); rare ANCA -ve |
High Yield: RPGN Classification
The RPGN classification by IF pattern is extremely high yield for exams. Remember:
- Linear = anti-GBM (Type I)
- Granular = immune complex (Type II)
- Negative = pauci-immune/ANCA (Type III)
Etiology of RPGN (from GC lecture slides): Pauci-immune GN (systemic vasculitis), Anti-GBM disease / Goodpasture syndrome, Crescentic IgAN, Acute postinfectious GN [5]
Frequency: T1 > T3 > T2 in terms of how rapidly they progress, but Type III (pauci-immune) is the most common cause overall [1][4]
| Subtype | Proportion | Features |
|---|---|---|
| Pulmonary-renal syndrome (Goodpasture's syndrome) | ~40–60% | Both RPGN + alveolar haemorrhage; younger patients, smokers |
| Renal-limited anti-GBM disease | ~40% | RPGN without lung involvement; older patients, non-smokers |
| Isolated pulmonary haemorrhage | ~5–10% | Rare; lung haemorrhage without significant renal disease |
| Double-positive disease (anti-GBM + ANCA) | ~10–50% of anti-GBM patients | Overlap features; may have slightly better renal prognosis |
Under the KDIGO framework, anti-GBM disease is classified as:
- Immune complex and complement-mediated GN → specifically under "Anti-GBM nephritis"
- Distinguished from immune complex GN (e.g., lupus nephritis, IgAN) and pauci-immune GN (ANCA-associated)
7. Clinical Features
Anti-GBM disease presents as RPGN ± pulmonary haemorrhage [2][3].
The presentation is typically:
- Acute or subacute onset (days to weeks)
- "Abrupt onset of S/S of GN, eg. haematuria, proteinuria, RBC casts" [4]
- "Rapidly declining renal function leading to ESRD in days to weeks" [4]
- "Often preceded by insidious onset of fatigue or oedema" [4]
- A preceding flu-like prodrome or upper respiratory tract infection may be present (but is not necessary)
7.2 Symptoms (with Pathophysiological Basis)
| Symptom | Mechanism |
|---|---|
| Macroscopic (gross) haematuria — tea-/cola-coloured urine | Anti-GBM Ab binding → GBM breaks → RBCs leak into Bowman's space and tubules → visible blood in urine. The colour is "smoky" or "cola" because RBCs are lysed/deformed during tubular transit |
| Oliguria / anuria | Crescents compress and obliterate the capillary tuft → ↓↓ GFR → ↓ urine output. When > 50% of glomeruli have crescents, oliguria is expected |
| Fatigue, malaise | Uraemia from rapidly declining GFR → accumulation of uraemic toxins (urea, creatinine, phosphate, indoxyl sulphate). "Often preceded by insidious onset of fatigue" [4] |
| Oedema | ↓ GFR → sodium and water retention → peripheral oedema. Note: "often preceded by insidious onset of... oedema" [4] |
| Nausea, vomiting, anorexia | Uraemic symptoms from rapidly rising creatinine |
| Flank/loin pain | Renal capsular distension from inflammation (uncommon) |
| Symptom | Mechanism |
|---|---|
| Dyspnoea (SOB) | Anti-GBM antibodies bind alveolar basement membrane → alveolar haemorrhage → blood fills alveoli → impaired gas exchange → hypoxaemia → SOB [2] |
| Cough | Blood in the airways irritates cough receptors |
| Haemoptysis | Direct expectoration of blood from alveolar haemorrhage. "S/S: SOB, cough, sometimes overt haemoptysis" [2]. Note: haemoptysis may be absent even with significant pulmonary haemorrhage (blood may remain in the alveoli without reaching the airways) |
| Chest tightness | Alveolar flooding reduces compliance |
"Alveolar haemorrhage (40-60%)" in anti-GBM disease [2]
Occult Pulmonary Haemorrhage
Not all patients with DAH have haemoptysis. A patient may have significant alveolar haemorrhage causing anaemia and CXR infiltrates without ever coughing up blood. Always check DLCO and CXR even if haemoptysis is absent. "Iron-deficiency anaemia if occult" [2] — chronic occult pulmonary bleeding causes iron to be sequestered in the lungs as haemosiderin.
| Symptom | Mechanism |
|---|---|
| Malaise, weight loss | Non-specific inflammatory response; uraemia |
| Low-grade fever | Inflammatory cytokine release (IL-1, IL-6, TNF-α from macrophages in crescents) |
| Arthralgia (rare, if double-positive with ANCA) | ANCA-associated systemic vasculitis overlap |
7.3 Signs (with Pathophysiological Basis)
| Sign | Mechanism |
|---|---|
| Hypertension | ↓ GFR → sodium and water retention → volume expansion → ↑ BP. Also RAAS activation from renal ischaemia (crescents compress the capillary tuft → juxtaglomerular apparatus senses ↓ perfusion → renin release) |
| Peripheral oedema (pitting) | Fluid overload from ↓ GFR and Na/water retention |
| Pulmonary oedema (bibasal crackles) | Fluid overload in the setting of AKI; also possible alveolar haemorrhage contributing to crackles |
| Uraemic signs (if advanced): pericardial rub, asterixis, uraemic frost (rare) | Uraemic toxin accumulation in severe AKI; pericardial rub = uraemic pericarditis; asterixis = metabolic encephalopathy |
| Sign | Mechanism |
|---|---|
| Bilateral inspiratory crackles | Blood in the alveoli → fluid crackles on auscultation (may mimic pulmonary oedema) |
| Tachypnoea | Hypoxaemia from impaired gas exchange drives respiratory rate up (peripheral and central chemoreceptor activation) |
| Pallor | Iron-deficiency anaemia from chronic occult pulmonary haemorrhage (iron trapped as haemosiderin in alveolar macrophages) |
| Cyanosis (if severe) | Severe hypoxaemia from extensive alveolar flooding |
| Notable Absence | Significance |
|---|---|
| No rash, no arthritis, no oral ulcers | Anti-GBM disease is organ-specific (kidney ± lung only). Unlike SLE or ANCA vasculitis, there are no systemic vasculitic features such as purpura, skin ulcers, neuropathy, or arthritis (unless double-positive with ANCA) |
| No sinusitis, no nasal crusting | Distinguishes from GPA (Wegener's) which has ENT involvement |
| Finding | Mechanism |
|---|---|
| Dysmorphic RBCs | RBCs pass through damaged GBM → mechanical distortion through glomerular pores and osmotic stress in tubules → characteristic "Mickey Mouse ear" morphology on phase-contrast microscopy [2] |
| RBC casts | RBCs aggregate within Tamm-Horsfall protein matrix in the distal tubule/collecting duct → pathognomonic of glomerular bleeding (as opposed to lower urinary tract bleeding). "Nephritic sediments in urinalysis (dysmorphic RBCs, WBCs, RBC/granular casts)" [2] |
| WBCs / WBC casts | Inflammatory cell infiltration of the glomerulus |
| Proteinuria (usually sub-nephrotic) | GBM damage → loss of charge and size selectivity → protein leakage. "Proteinuria: usually non-nephrotic" [2]. "Proteinuria usually not florid as daily protein excretion is limited by ↓↓GFR" [4] — because the GFR is so severely reduced that there isn't enough filtered volume to generate > 3.5 g/day of protein loss |
| Granular casts | Degenerated cellular casts; indicate tubular damage |
Why is Proteinuria Sub-Nephrotic in RPGN?
This is a common exam question. In anti-GBM disease (and RPGN in general), although there is severe glomerular damage, the proteinuria is typically sub-nephrotic ( < 3.5 g/day). This seems paradoxical — if the GBM is destroyed, shouldn't more protein leak through?
The answer: "Proteinuria usually not florid as daily protein excretion is limited by ↓↓GFR" [4]. The GFR is so severely reduced (often < 15 mL/min) that the absolute volume of filtrate reaching the damaged glomeruli is tiny. Less filtrate = less protein filtered, even though the permeability barrier is wrecked. Think of it as: if you punch holes in a sieve but also dramatically reduce the water flow through it, not much leaks through despite the holes.
| Finding | Basis |
|---|---|
| Elevated serum creatinine (often > 250 μmol/L at diagnosis [4]) | Crescent formation → ↓↓ GFR → creatinine accumulation |
| Raised CRP / ESR | Acute inflammatory response |
| Iron-deficiency anaemia | "Iron-deficiency anaemia if occult" [2] — chronic DAH → iron sequestration in lungs |
| Normocytic anaemia | Anaemia of chronic kidney disease (↓ EPO production + uraemic bone marrow suppression) + blood loss |
| ↑ DLCO | "↑DLCO due to haemoglobin in alveoli" [2] — haemoglobin in the alveolar space binds carbon monoxide during the DLCO test → falsely elevated transfer factor. This is counterintuitive (you'd expect lung disease to ↓ DLCO) but is highly specific for alveolar haemorrhage |
| CXR: pulmonary infiltrates | "CXR: pulmonary infiltrates" [2] — bilateral, diffuse, alveolar infiltrates from blood in the alveoli. Typically spares the apices and costophrenic angles |
| Hyperkalaemia | ↓ GFR → impaired K+ excretion |
| Metabolic acidosis (raised anion gap) | ↓ GFR → impaired H+ excretion and ↓ bicarbonate regeneration |
DLCO in Alveolar Haemorrhage — Counter-intuitive but High Yield
Normally, interstitial lung disease ↓ DLCO because the gas exchange membrane is thickened. In alveolar haemorrhage, DLCO is paradoxically elevated because free haemoglobin in the alveolar spaces acts as a "CO sink" — it avidly binds the carbon monoxide used in the test, making it appear as though gas transfer is enhanced. This is a classic exam question.
RPGN is a clinical syndrome, NOT a specific aetiological form of GN [1][3][4][5].
Anti-GBM disease is one of the causes of RPGN (Type I). Key features from the GC lecture slides:
"Etiology [of RPGN]: Pauci-immune GN (systemic vasculitis), Anti-GBM disease / Goodpasture syndrome, Crescentic IgAN, Acute postinfectious GN" [5]
RPGN clinical features include:
- Haematuria, proteinuria and ↓↓RFT that leads to ESRD within 2 weeks of onset if untreated [3]
- Histology: > 50% glomeruli with crescent [3]
Management of RPGN: "usually require IV pulse steroids ± other immunosuppressants (e.g. cyclophosphamide, rituximab)" [3]
"Plasma exchange for fulminant MPA / GPA or Goodpasture's syndrome" [3]
While formal diagnosis/workup will be covered in the next section, understanding the histological basis aids clinical comprehension:
| Modality | Findings | Significance |
|---|---|---|
| Light Microscopy (LM) | "Cellular crescents (majority), segmental fibrinoid necrosis, GBM breaks" [2] | Crescents = proliferating parietal epithelial cells + macrophages + fibrin in Bowman's space; fibrinoid necrosis = acute severe vascular injury |
| Electron Microscopy (EM) | "GBM disruption w/o significant immune deposits" [2] | Unlike immune complex GN (e.g., lupus), there are NO electron-dense deposits. The damage is from direct antibody binding, not immune complex deposition |
| Immunofluorescence (IF) | "Characteristic linear IgG/C3 staining along GBM" [2] | Pathognomonic finding. Linear = antibodies coating the GBM uniformly (like paint on a wall), as opposed to granular = lumpy deposits of immune complexes |
| Clinical Feature | ← Pathophysiological Link |
|---|---|
| RPGN (rapid renal failure) | Anti-GBM Ab → GBM destruction → crescent formation → obliterated glomeruli → ↓↓ GFR |
| Haematuria + RBC casts | GBM breaks → RBCs enter Bowman's space → tubular transit → dysmorphic RBCs + casts |
| Sub-nephrotic proteinuria | GBM permeability barrier destroyed BUT ↓↓ GFR limits total protein excretion |
| Pulmonary haemorrhage | Same Ab binds alveolar BM (exposed by smoking/infection) → capillaritis → DAH |
| ↑ DLCO | Free Hb in alveoli binds CO during test |
| Iron-deficiency anaemia | Chronic DAH → iron trapped as haemosiderin in lungs |
| Linear IF on biopsy | Uniform Ab coating along GBM (not lumpy immune complex deposits) |
| Bimodal age distribution | Young smokers → full Goodpasture's; Older non-smokers → renal-limited |
High Yield Summary
Anti-GBM Disease — Key Points:
-
Definition: Autoimmune disease with IgG antibodies against the NC1 domain of α3 chain of type IV collagen (Goodpasture antigen) in the GBM (and alveolar BM)
-
Goodpasture's syndrome = anti-GBM disease + pulmonary haemorrhage (40–60% of cases)
-
Epidemiology: Rare (1.64/million/year), bimodal (young males = lung + kidney; older patients = kidney only), 15–20% of RPGN
-
Key risk factor for lung involvement: SMOKING (exposes the normally sequestered alveolar basement membrane antigen)
-
HLA association: HLA-DRB1*1501/1502
-
Pathognomonic finding: Linear IgG staining on immunofluorescence (Type I RPGN)
-
EM: GBM disruption without immune deposits (distinguishes from immune complex GN)
-
Clinical presentation: RPGN (haematuria, RBC casts, rapidly rising creatinine, oliguria) ± pulmonary haemorrhage (SOB, haemoptysis, CXR infiltrates, ↑DLCO)
-
Proteinuria is sub-nephrotic because ↓↓GFR limits total protein excretion
-
↑DLCO is counterintuitive but occurs because haemoglobin in alveoli binds CO
-
ANCA co-positivity in 10–50% — indicates better treatment response
-
Post-transplant anti-GBM can occur in Alport syndrome patients receiving a normal kidney
-
Without treatment: > 90% → dialysis or death
-
RPGN classification (IF-based): Type I (linear) = anti-GBM; Type II (granular) = immune complex; Type III (negative) = pauci-immune/ANCA
Active Recall - Anti-GBM Disease (Definition, Epidemiology, Risk Factors, Pathophysiology, Clinical Features)
[1] Adrian Lui Pediatrics Notes.pdf (p. 326 — RPGN section) [2] Ryan Ho Urogenital.pdf (p. 67 — Section 3.3.3 Anti-Glomerular Basement Membrane Antibody Disease) [3] Maksim Medicine Notes.pdf (p. 231–233 — Crescentic/RPGN section, Anti-GBM disease table) [4] Ryan Ho Fundamentals.pdf (p. 361 — RPGN section) [5] GC 057. Glomerular and Tubulo-interstitial Diseases and Acute Kidney Injury.pdf (p. 10, 50 — Classification and Etiology of RPGN)
Differential Diagnosis of Anti-GBM Disease
Anti-GBM disease presents in two main clinical scenarios, each with its own differential diagnosis framework:
- Rapidly progressive glomerulonephritis (RPGN) — the renal presentation
- Pulmonary-renal syndrome — the combined lung haemorrhage + RPGN presentation
The differential must be worked through systematically because treatment differs dramatically between causes, and anti-GBM disease is a medical emergency where hours matter. The wrong diagnosis → wrong treatment → irreversible renal failure.
"RPGN is a clinical syndrome, NOT a specific aetiological form of GN" — it can be caused by many diseases, so the differential must be narrowed by serology, complement levels, and biopsy [1][4]
The most useful way to approach the differential of anti-GBM disease (presenting as RPGN) is the IF-based classification of RPGN [1][3][4]:
High Yield — GC Lecture Slides: Etiology of RPGN
Etiology of RPGN (from GC 057):
- Pauci-immune GN (systemic vasculitis)
- Anti-GBM disease / Goodpasture syndrome
- Crescentic IgAN
- Acute postinfectious GN [5]
These four causes are the core differential for RPGN and are extremely high yield for the in-house exam.
Before the biopsy result returns, serum complement levels are one of the most powerful tools to narrow the differential diagnosis [1][4][6]:
| Complement Level | Interpretation | Differentials |
|---|---|---|
| ↓ C3/C4 | Generally indicates immune complex-mediated GN [4][6] | MPGN, PSGN, lupus nephritis, cryoglobulinaemia, infective endocarditis, shunt nephritis [4][6] |
| Normal C3/C4 | Generally indicates non-immune-complex-mediated GN [4][6] | Anti-GBM disease (Goodpasture), ANCA-associated vasculitis (GPA/MPA/EGPA), HSP/IgAN, PAN [4][6] |
"Serum complement level: important in helping narrow the differential diagnosis" [4][6]
"↓C3/4 generally indicates IC-mediated GN — D/dx: MPGN, PSGN, lupus, cryoglobulinaemia, IE and shunt nephritis" [4][6]
"Normal C3/4 generally indicates non-IC-mediated GN (except IgAN) — D/dx: PAN, Goodpasture, HSP/IgAN, ANCA-related renal vasculitis" [4][6]
Why is complement normal in anti-GBM disease? Because anti-GBM disease causes in situ antibody binding along the GBM — the complement activation occurs locally at the glomerulus, consuming relatively small amounts of complement that are readily replaced by the liver. In contrast, immune complex GN (e.g., lupus) involves massive circulating immune complex formation that consumes complement systemically, causing measurably low serum levels.
Why is complement normal in ANCA vasculitis? ANCA vasculitis is pauci-immune — there are no significant immune deposits at all. Neutrophil activation is the primary pathogenic mechanism, not complement-mediated injury. (Note: the alternative complement pathway does play a role in ANCA vasculitis pathogenesis, but not enough to detectably lower serum complement.)
IgAN — The Exception
"IgA-IgG immune complex in IgAN does NOT activate complement" [6] — this is why IgAN has normal complement despite being an immune complex disease. The IgA1-containing immune complexes in IgAN predominantly activate the lectin pathway or alternative pathway weakly, and do not efficiently activate the classical pathway (which is the main consumer of C3/C4). So IgAN sits in the "normal complement" group despite technically being an immune complex GN.
4. Detailed Differential Diagnosis: Condition-by-Condition
This is our index condition. Key distinguishing features:
| Feature | Anti-GBM Disease |
|---|---|
| Serology | Anti-GBM antibody +ve [2][3] |
| IF pattern | Linear IgG/C3 along GBM [2] |
| Complement | Normal |
| ANCA | May be +ve in 10–50% [2] |
| Pulmonary involvement | 40–60% (esp. smokers) |
| Systemic vasculitic features | Absent (organ-specific: kidney ± lung only) |
| Course | Rapid → ESRD in days to weeks without treatment |
ANCA vasculitis is the most common cause of RPGN overall and is the single most important differential diagnosis for anti-GBM disease. It can also present with pulmonary-renal syndrome, making it clinically indistinguishable from anti-GBM disease without serology.
| Feature | GPA (Wegener's) | MPA | EGPA (Churg-Strauss) |
|---|---|---|---|
| ANCA | c-ANCA / anti-PR3 (90%) | p-ANCA / anti-MPO (60%) | p-ANCA / anti-MPO (40%) |
| IF | Negative (pauci-immune) | Negative | Negative |
| Complement | Normal | Normal | Normal |
| Key distinguishing features | Triad of sinusitis, pulmonary infiltrates (granulomas/cavities) and nephritis [4][6]; nasal crusting, saddle-nose deformity, subglottic stenosis | No upper airway involvement; pulmonary haemorrhage common; most common cause of pauci-immune RPGN | Asthma, eosinophilia ( > 10%), nasal polyposis, mononeuritis multiplex |
| Pulmonary involvement | Cavitating lung nodules/granulomas (different from DAH) | Diffuse alveolar haemorrhage (like anti-GBM) | Transient pulmonary infiltrates, asthma |
| Skin | Purpura, ulcers | Purpura, livedo reticularis | Purpura, subcutaneous nodules |
"Triad of sinusitis, pulmonary infiltrates and nephritis suggest Wegener's" [4][6]
Why this matters: Both ANCA vasculitis and anti-GBM disease can cause RPGN + pulmonary haemorrhage. The key clinical distinguisher is that ANCA vasculitis typically has extra-renal/extra-pulmonary systemic features (rash, neuropathy, sinusitis, arthralgia) while anti-GBM disease is organ-specific (kidney ± lung only, no rash, no sinusitis). However, 10–50% of anti-GBM patients are double-positive (anti-GBM + ANCA), making the picture even more complex — always send both ANCA and anti-GBM together.
4.3 Type II RPGN — Immune Complex-Mediated
| Feature | Lupus Nephritis | Anti-GBM Disease |
|---|---|---|
| Demographics | Young females (9:1 F:M) | Bimodal, slight male predominance |
| Systemic features | Characteristic rash (malar rash) and arthritis [4][6], oral ulcers, serositis, alopecia, photosensitivity | Kidney ± lung only |
| Serology | ANA +ve, anti-dsDNA +ve, ± anti-Smith | Anti-GBM +ve |
| Complement | ↓ C3/C4 (immune complex consumption) | Normal |
| IF | Granular "full house" pattern (IgG, IgA, IgM, C3, C1q) | Linear IgG/C3 |
| Haemoptysis | Rare (lupus pneumonitis, DAH can occur but uncommon) | 40–60% |
Why lupus causes low complement: SLE involves massive production of autoantibodies (anti-dsDNA) that form circulating immune complexes → these complexes deposit in glomeruli and also activate the classical complement pathway systemically → C3 and C4 are consumed at a rate faster than hepatic synthesis can replenish them → measurably low serum complement [7].
| Feature | PSGN | Anti-GBM Disease |
|---|---|---|
| Age | Children 5–12 years (most common cause of nephritis in children) | Young adults or > 50 years |
| Temporal relationship | 7–10 days after strep throat / 3–6 weeks after skin infection [3][8] | No consistent temporal relationship to infection |
| Course | Self-resolving (diuresis in 1–2 weeks, RFT normalises in 4 weeks) [8] | Rapidly progressive → ESRD without treatment |
| Complement | ↓ C3 (normalises by 4–8 weeks; if persists → consider lupus/MPGN) [3][8] | Normal |
| Serology | ASOT +ve, throat swab | Anti-GBM +ve |
| IF | Granular (IgG, C3 in "starry sky" pattern) | Linear |
| Pulmonary involvement | No | 40–60% |
"Relationship with URTI: URTI 7-10d before (PSGN) or concurrently (IgAN)" [4][6]
Why PSGN self-resolves but anti-GBM doesn't: In PSGN, the immune complexes are cleared over time by the reticuloendothelial system, and the offending antigen (streptococcal) is eliminated → inflammation subsides. In anti-GBM disease, the autoantibody directly and continuously binds the GBM itself (the antigen is part of the patient's own body), causing ongoing destruction until the antibody is removed or the kidney is destroyed.
| Feature | IgAN | Anti-GBM Disease |
|---|---|---|
| Epidemiology | Most common primary GN [3]; common in Hong Kong/East Asia | Rare |
| Temporal relationship | Synpharyngitic (gross haematuria within 1–2 days of URTI — concurrent, not delayed) [3][6][8] | No consistent temporal relationship |
| Usual course | Usually slowly indolent (RPGN in < 10%) | Always rapid (RPGN) |
| Complement | Normal (IgA does not efficiently activate classical complement) [6] | Normal |
| Serology | ↑ IgA in 50% [3]; anti-GBM negative | Anti-GBM +ve |
| IF | Granular — mesangial IgA dominant | Linear IgG |
| Recurrence | Recurrent episodic haematuria over years | Single episode (self-limited autoimmune response) |
"Recurrent synpharyngitic haematuria (gross haematuria within 1-2 days of URTI)" — the key distinguishing feature of IgAN [3]
Why IgAN is synpharyngitic (concurrent) while PSGN is post-infectious (delayed): In IgAN, mucosal infection stimulates the already-primed IgA immune system → immediate surge in polymeric IgA1 → rapid mesangial deposition → haematuria within 1–2 days. In PSGN, the immune response takes time to develop (antibody production against streptococcal antigens needs 1–3 weeks) → delayed presentation.
| Feature | MPGN | Anti-GBM Disease |
|---|---|---|
| Course | Can present acutely (may mimic PSGN) but usually persists beyond 4–6 weeks with further ↑Cr [8] | Rapid → ESRD in days/weeks |
| Complement | ↓ C3/C4 (hypocomplementaemia is a hallmark) [9][10] | Normal |
| Associations | HBV/HCV, SLE, cryoglobulinaemia, malignancy (CLL, MM) [9][10] | Smoking, HLA-DRB1*1501 |
| IF | Granular (C3, IgG) | Linear |
| Prognosis | Poor — 50% develop ESRD in 10 years [9][10] | > 90% ESRD if untreated; better if treated early |
| Feature | Cryoglobulinaemia | Anti-GBM Disease |
|---|---|---|
| Associations | HCV infection (most common), autoimmune diseases | Smoking, HLA-DRB1*1501 |
| Clinical features | Meltzer's triad: purpura, arthralgia, weakness; Raynaud's | Kidney ± lung only |
| Complement | ↓ C4 (disproportionately low) | Normal |
| Diagnosis | Cryocrit +ve [4][6] | Anti-GBM Ab +ve |
| Condition | Key Distinguishing Feature |
|---|---|
| Henoch-Schönlein Purpura (HSP) | Tetrad: palpable purpura (buttocks/lower limbs), arthralgia, abdominal pain, renal disease; children; histology identical to IgAN (mesangial IgA); complement normal [11] |
| Drug-induced crescentic GN (e.g., hydralazine, penicillamine) | Drug exposure history; may be ANCA-positive |
| Thrombotic microangiopathy (TMA) / HUS-TTP | Microangiopathic haemolytic anaemia (schistocytes), thrombocytopaenia; no significant immune deposits on biopsy |
When a patient presents with both RPGN and pulmonary haemorrhage, the differential is more focused:
| Cause | Key Distinguishing Features |
|---|---|
| Anti-GBM disease / Goodpasture's | Anti-GBM Ab +ve; linear IF; no systemic vasculitic features; smokers |
| ANCA vasculitis (GPA, MPA) | ANCA +ve; pauci-immune IF; systemic features (sinusitis in GPA, purpura, neuropathy) |
| SLE | ANA/anti-dsDNA +ve; young female; malar rash, arthritis, serositis; ↓ complement; granular IF |
| Double-positive disease (anti-GBM + ANCA) | Both anti-GBM and ANCA positive; overlap features |
| IgA vasculitis (HSP) with DAH | Very rare; palpable purpura, children |
| Cryoglobulinaemia | HCV association; ↓ C4; cryocrit +ve |
"Haemoptysis suggest pulmonary haemorrhage (pulmonary vasculitis)" [4][6]
"± extrarenal features, eg. haemoptysis (Goodpasture), vasculitic rash (ANCA vasculitis)" [4]
When a patient presents with suspected RPGN, the following serological panel is sent simultaneously (do NOT wait for one result before sending the next — time is critical):
Workup: CBC, RFT, urinalysis; Complement; Serology: ANCA, anti-GBM, ANA, anti-dsDNA; CXR, DLCO for pulmonary involvement; ± renal biopsy [1][4]
| Test | What It Rules In/Out | Why |
|---|---|---|
| Anti-GBM Ab (ELISA) | Anti-GBM disease | Directly detects the pathogenic autoantibody |
| ANCA (IIF + ELISA for PR3/MPO) | ANCA vasculitis (GPA/MPA/EGPA) | Detects the autoantibody driving neutrophil activation |
| ANA, anti-dsDNA | SLE / lupus nephritis | Highly specific (anti-dsDNA) for SLE |
| C3, C4 | Separates IC-mediated (low) from non-IC (normal) | See complement trick above |
| ASOT / streptozyme | PSGN | Confirms recent streptococcal infection |
| HBV/HCV serology | HBV/HCV-related MPGN or membranous nephropathy | Treatable cause |
| Cryocrit | Cryoglobulinaemia | When HCV +ve or clinical suspicion |
| Blood cultures | Infective endocarditis | When persistent fever + murmur |
| CXR | Pulmonary haemorrhage (bilateral infiltrates) vs infection vs fluid overload | First-line imaging |
| DLCO | Alveolar haemorrhage (↑DLCO = pathognomonic) | Even without overt haemoptysis |
| Renal biopsy | Definitive diagnosis — IF pattern most helpful [4][6] | Distinguishes Type I/II/III RPGN definitively |
"Serology for relevant conditions: ANCA and its subtypes for ANCA-vasculitis; ANA, anti-dsDNA for lupus nephritis; Anti-GBM autoAb for anti-GBM disease; Anti-streptolysin O (ASLO) for PSGN; Anti-HCV, HBV for HBV/HCV-related MPGN" [4][6]
These are the suggestive clinical findings from the senior notes that point toward specific diagnoses [4][6]:
| Clinical Clue | Points Toward | Why |
|---|---|---|
| URTI 7–10 days before | PSGN | Latent period for immune complex formation after streptococcal infection [4][6] |
| Concurrent with URTI (synpharyngitic) | IgAN | Pre-existing IgA dysregulation → immediate IgA surge on mucosal stimulation [4][6] |
| Palpable purpura / petechial rash | Vasculitis (ANCA, HSP, cryoglobulinaemia) | Leukocytoclastic vasculitis in dermal small vessels [4][6] |
| Haemoptysis | Anti-GBM, ANCA vasculitis (pulmonary-renal syndrome) | Anti-GBM Ab or ANCA-mediated pulmonary capillaritis [4][6] |
| Sinusitis + pulmonary infiltrates + nephritis | GPA (Wegener's) | Granulomatous vasculitis in upper/lower airways + kidneys [4][6] |
| Malar rash + arthritis | SLE | Immune complex deposition in skin and joints [4][6] |
| Persistent fever + new murmur | Infective endocarditis | Infected valvular vegetations → circulating immune complexes → GN [4][6] |
| Smoking history | Pulmonary involvement in anti-GBM | Exposes alveolar basement membrane antigen [2] |
| Flank pain + URTI in a young male | IgAN | Renal capsular stretch from acute IgA mesangial inflammation |
| Child with purpura + abdo pain + arthralgia | HSP | IgA vasculitis affecting skin, joints, GI, kidneys [11] |
| Condition | RPGN Type | IF Pattern | Anti-GBM | ANCA | Complement | Key Feature |
|---|---|---|---|---|---|---|
| Anti-GBM disease | I | Linear | +ve | ± (10–50%) | Normal | Organ-specific (kidney ± lung) |
| GPA | III | Negative | −ve | c-ANCA/PR3 | Normal | Sinusitis, lung granulomas |
| MPA | III | Negative | −ve | p-ANCA/MPO | Normal | DAH, purpura, neuropathy |
| EGPA | III | Negative | −ve | p-ANCA/MPO | Normal | Asthma, eosinophilia |
| Lupus nephritis | II | Granular (full house) | −ve | −ve | ↓↓ | Malar rash, arthritis, young F |
| PSGN | II | Granular | −ve | −ve | ↓ C3 | Post-pharyngitis; self-resolving |
| IgAN (crescentic) | II | Granular (mesangial IgA) | −ve | −ve | Normal | Synpharyngitic; recurrent |
| MPGN | II | Granular | −ve | −ve | ↓↓ | HBV/HCV; chronic course |
| Cryoglobulinaemia | II | Granular | −ve | −ve | ↓ C4 | HCV; Raynaud's; purpura |
| HSP | II | Granular (mesangial IgA) | −ve | −ve | Normal | Children; purpura + abdo pain |
| Double +ve (anti-GBM + ANCA) | I + III | Linear ± pauci | +ve | +ve (MPO) | Normal | Overlap features; better Tx response |
High Yield Summary — Differential Diagnosis of Anti-GBM Disease
-
Always send anti-GBM, ANCA, ANA/anti-dsDNA, complement, and ASOT simultaneously — do not wait for results sequentially; RPGN is a time-critical emergency
-
Complement levels split the differential: ↓C3/C4 = immune complex (lupus, PSGN, MPGN, cryoglobulinaemia, IE); Normal C3/C4 = anti-GBM, ANCA vasculitis, IgAN, HSP
-
IF pattern on renal biopsy is the definitive differentiator: Linear = anti-GBM; Granular = immune complex; Negative = pauci-immune/ANCA
-
The two most important differentials for pulmonary-renal syndrome: ANCA vasculitis (GPA/MPA) and anti-GBM disease. ANCA vasculitis has systemic features (rash, sinusitis, neuropathy); anti-GBM is organ-specific (kidney ± lung only)
-
10–50% of anti-GBM patients are ANCA co-positive — always send both; double-positive disease has slightly better treatment response
-
PSGN self-resolves; anti-GBM does not — the critical distinction in a child/young adult with acute nephritis
-
IgAN complement is NORMAL despite being immune complex-mediated (IgA does not efficiently activate classical complement) — don't be fooled
Active Recall — Differential Diagnosis of Anti-GBM Disease
References
[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 326 — RPGN section) [2] Senior notes: Ryan Ho Urogenital.pdf (p. 67 — Section 3.3.3 Anti-GBM Disease) [3] Senior notes: Maksim Medicine Notes.pdf (p. 231–233 — Anti-GBM and RPGN sections) [4] Senior notes: Ryan Ho Fundamentals.pdf (p. 360–361 — Evaluation and RPGN classification) [5] Lecture slides: GC 057. Glomerular and Tubulo-interstitial Diseases and Acute Kidney Injury.pdf (p. 50 — Etiology of RPGN) [6] Senior notes: Ryan Ho Urogenital.pdf (p. 63 — Evaluation of nephritic syndrome) [7] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 415 — Biochemical tests / complement) [8] Senior notes: Ryan Ho Urogenital.pdf (p. 66 — PSGN clinical features and laboratory features) [9] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p. 405 — MPGN) [10] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p. 998 — MPGN) [11] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 460 — HSP)
Diagnostic Criteria, Diagnostic Algorithm, and Investigations for Anti-GBM Disease
1. Diagnostic Criteria
Anti-GBM disease does not have a single "set of criteria" like the ACR/EULAR criteria for SLE or the Jones criteria for rheumatic fever. Instead, diagnosis relies on a combination of clinical presentation, serological confirmation, and histopathological findings. Think of it as a tripod — you need clinical suspicion + serology + biopsy to be confident.
The diagnosis of anti-GBM disease requires at least one of the following two (ideally both):
| Criterion | Details | Why It's Diagnostic |
|---|---|---|
| 1. Serological: Positive circulating anti-GBM antibodies | Detected by ELISA (most common) or Western blot targeting the NC1 domain of α3(IV) collagen | Directly identifies the pathogenic autoantibody. Sensitivity ~95%, specificity > 97% by modern ELISA [2] |
| 2. Histopathological: Linear IgG staining along the GBM on immunofluorescence on renal biopsy | "IF: characteristic linear IgG/C3 staining along GBM" [2] | Pathognomonic — no other condition produces this pattern with this clinical context |
In clinical practice, you typically have both — positive serology AND confirmatory biopsy. However:
- If serology is strongly positive and the patient is too sick for biopsy (e.g., on ventilator with DAH, coagulopathy), treatment may be started on serology alone
- If serology is negative but clinical suspicion is very high, biopsy may reveal the diagnosis (rare "seronegative" anti-GBM disease — antibodies present in tissue but below detection threshold in serum)
"Practice Point 1.1.1: The kidney biopsy is the 'gold standard' for the diagnostic evaluation of glomerular diseases. However, under some circumstances, treatment may proceed without a kidney biopsy confirmation of diagnosis" — KDIGO GN Guideline 2021 [5]
High Yield — GC Lecture: Biopsy as Gold Standard
The kidney biopsy is the "gold standard" for the diagnostic evaluation of glomerular diseases [5]. This is a direct GC lecture-slide point from KDIGO 2021 guidelines. However, in the specific context of anti-GBM disease, treatment should NEVER be delayed waiting for biopsy — if anti-GBM serology is positive and clinical picture fits, start treatment immediately (IV methylprednisolone + plasma exchange). Biopsy can follow once the patient is stabilised.
| Feature | Finding | Interpretation |
|---|---|---|
| Clinical presentation | RPGN ± pulmonary haemorrhage | Fits the anti-GBM phenotype |
| Complement C3/C4 | Normal | Rules against immune complex GN (Type II RPGN) |
| ANCA | May be positive (10–50%) | Does not exclude anti-GBM; double-positive disease exists [2] |
| Renal biopsy — LM | "Cellular crescents, segmental fibrinoid necrosis, GBM breaks" [2] | Confirms crescentic GN |
| Renal biopsy — EM | "GBM disruption w/o significant immune deposits" [2] | Distinguishes from immune complex GN (no electron-dense deposits) |
| CXR | Bilateral pulmonary infiltrates | Supports alveolar haemorrhage |
| DLCO | ↑ DLCO | "↑DLCO due to haemoglobin in alveoli" [2] — pathognomonic of alveolar haemorrhage |
| Level | Basis | Action |
|---|---|---|
| Definite | Anti-GBM Ab +ve AND renal biopsy showing linear IgG on IF with crescentic GN | Confirmed diagnosis |
| Probable | Anti-GBM Ab +ve with compatible clinical picture (RPGN ± DAH); biopsy not yet done or not feasible | Start treatment; biopsy when safe |
| Possible | RPGN with pulmonary haemorrhage, serology pending | Send anti-GBM + ANCA urgently; can give empirical pulse IV methylprednisolone while awaiting results [1][4] |
| Seronegative anti-GBM | Anti-GBM Ab negative by ELISA but biopsy shows linear IgG on IF | Rare (~5%); treat as anti-GBM disease |
Seronegative Anti-GBM Disease
A small proportion of patients (~2–5%) have negative serum anti-GBM antibodies by standard ELISA but show classic linear IgG on biopsy. This can occur because:
- The antibody titre is very low (below ELISA detection threshold)
- The antibodies are directed against atypical epitopes not captured by the assay
- Antibodies are all bound to tissue with little remaining in circulation
This is why renal biopsy remains the gold standard — you should never definitively rule out anti-GBM disease on serology alone if clinical suspicion is high.
2. Diagnostic Algorithm
The diagnostic workup follows a parallel, time-critical approach — investigations are sent simultaneously, not sequentially.
-
Never wait for serology before starting treatment if clinical suspicion is high: "Can give empirical pulse IV methylprednisolone before renal Bx if indicated" [1][4]. If a patient presents with RPGN + DAH, give pulse methylprednisolone and arrange plasma exchange while serology is pending.
-
Send anti-GBM AND ANCA together: Because 10–50% of patients are double-positive, and the distinction matters for treatment and prognosis [2].
-
Complement levels narrow the differential before serology returns: Normal complement → anti-GBM or ANCA vasculitis (treat aggressively). Low complement → immune complex GN (different treatment pathway) [1][4][6].
-
Biopsy as soon as safely feasible: Even with positive serology, biopsy provides:
-
Do NOT biopsy if kidneys are small (chronic irreversible disease) — "Renal biopsy: necessary for most cases of nephritic syndrome unless very small kidney on USG" [4][6]
3. Investigation Modalities — Detailed Breakdown
| Test | Expected Finding in Anti-GBM | Interpretation |
|---|---|---|
| Urine dipstick | Blood +++, Protein ++ to +++ | Quick bedside confirmation of glomerular disease |
| Urine microscopy | Dysmorphic RBCs, RBC casts [2][6] | Dysmorphic RBCs = glomerular origin (cells distorted passing through damaged GBM); RBC casts = pathognomonic of glomerular bleeding (RBCs trapped in Tamm-Horsfall protein gel in tubules) |
| WBCs / WBC casts | May be present | Inflammatory infiltrate in glomeruli |
| Granular casts | May be present | Degenerated cellular casts; indicate tubular injury |
| Urine protein quantification (spot UACR or 24h) | Usually sub-nephrotic ( < 3.5 g/day) [2] | Because ↓↓ GFR limits total protein filtration |
"Urinalysis: document glomerular haematuria, proteinuria and sterile pyuria" [4][6]
"All Hb-positive dipstick should be accompanied by urine microscopy to differentiate haematuria vs pigmenturia" [12]
Why dysmorphic RBCs? Red blood cells that pass through the damaged GBM are mechanically distorted by squeezing through small breaks and gaps → they lose their normal biconcave disc shape and develop irregular protrusions ("acanthocytes" with Mickey-Mouse ear projections). They are then further distorted by osmotic changes as they travel through tubules with varying tonicity. By contrast, isomorphic (normal-shaped) RBCs suggest a lower urinary tract source (bladder, prostate, urethra) where RBCs enter the urine without passing through a filtration barrier [12].
Why RBC casts are pathognomonic of glomerular bleeding? RBCs leaking from damaged glomeruli travel down the tubule, where they become embedded in Tamm-Horsfall glycoprotein (secreted by tubular epithelial cells). This glycoprotein matrix gels together forming a cylindrical "cast" of the tubule shape, trapping the RBCs inside. This can only happen if the RBCs originated from the glomerulus — RBCs from the bladder or lower tract never enter the tubular system.
| Test | Expected Finding | Why |
|---|---|---|
| CBC | NcNc anaemia with ↓Hct [1][4][6]; ± iron-deficiency features (microcytic hypochromic) if chronic DAH; normal WBC (unless infection); normal platelets | Anaemia from renal failure (↓EPO) + blood loss (DAH). If platelets low → consider TMA/HUS as alternative |
| RFT | ↑ Creatinine (often > 250 μmol/L at diagnosis) [4]; ↑ urea; ↓ eGFR; hyperkalaemia; metabolic acidosis | Documents severity of AKI and need for dialysis |
| ESR | Usually increased [1][4][6] | Non-specific acute phase reactant |
| CRP | May be elevated | Non-specific inflammation marker |
| LFT | Usually normal | Baseline before immunosuppression |
| Coagulation screen | Normal (unless DIC or anticoagulant use) | Pre-biopsy safety check |
"Preliminary tests: CBC: NcNc anaemia with ↓Hct ± ↑WBC (if recent infection); RFT: document degree of renal impairment; ESR: usually increased" [1][4][6]
This is the most important set of tests. All should be sent simultaneously and urgently (ideally with a verbal "urgent" request to the lab).
| Test | Expected in Anti-GBM | Sensitivity/Specificity | Interpretation |
|---|---|---|---|
| Anti-GBM antibody (ELISA) | Positive [2][3] | Sensitivity ~95%, Specificity > 97% | Detects circulating IgG against NC1 domain of α3(IV) collagen. "Anti-GBM antibodies in serum, usually by ELISA" [2]. Can also use Western blot or biosensor assays for atypical cases |
| ANCA (IIF screen + PR3/MPO ELISA) | May be positive in 10–50% [2] | Variable | Screens for co-existent ANCA vasculitis. If ANCA +ve alone (anti-GBM −ve) → ANCA vasculitis, not anti-GBM. "ANCA: may be present in 10-50% anti-GBM pt, indicates better response to Tx" [2] |
| ANA | Negative (usually) | — | If +ve → consider SLE |
| Anti-dsDNA | Negative | — | If +ve → lupus nephritis |
| C3, C4 | Normal | — | "Complement: normal in Type I and III; ↓ in Type II only" [1][4]. If low → IC-mediated GN (PSGN, lupus, MPGN) |
| ASOT / streptozyme | Negative | — | If +ve → PSGN |
| HBV/HCV serology | Negative (usually) | — | "Anti-HCV, HBV for HBV/HCV-related MPGN" [4][6] |
| Cryocrit | Negative | — | "Cryocrit for cryoglobulinaemia when clinically indicated" [4][6] |
| Blood cultures | Negative | — | "Blood culture for infection when clinically indicated (eg. persistent fever)" [4][6] |
"Serology for relevant conditions: ANCA and its subtypes for ANCA-vasculitis; ANA, anti-dsDNA for lupus nephritis; Anti-GBM autoAb for anti-GBM disease; Anti-streptolysin O (ASLO) for PSGN" [4][6]
Workup: "CBC, RFT, urinalysis; Complement; Serology: ANCA, anti-GBM, ANA, anti-dsDNA; CXR, DLCO for pulmonary involvement; ± renal biopsy" [1][4]
Why Send All Serologies Simultaneously?
Anti-GBM disease is a medical emergency — delays of even 24–48 hours in diagnosis and treatment can mean the difference between salvageable kidneys and permanent dialysis dependence. ANCA results may take days. Anti-GBM ELISA results may take 24–48 hours. You cannot afford to send them sequentially. Furthermore, 10–50% of patients are double-positive (anti-GBM + ANCA), so you need both to guide treatment properly.
Understanding the Anti-GBM ELISA:
- ELISA = Enzyme-Linked ImmunoSorbent Assay
- "Immuno" = uses antibodies; "Sorbent" = bound to a solid surface; "Enzyme-Linked" = enzyme conjugate produces a colour change proportional to antibody concentration
- The assay plate is coated with recombinant NC1 domain of α3(IV) collagen (the Goodpasture antigen)
- Patient serum is added → if anti-GBM IgG is present, it binds to the antigen
- An enzyme-linked secondary anti-human IgG antibody is added → colour change measured by spectrophotometry
- Quantitative result: antibody titre correlates with disease activity and can be used to monitor treatment response
- Serial monitoring: anti-GBM titres should fall with plasma exchange and immunosuppression; persistent elevation suggests ongoing antibody production
| Modality | Expected Finding | Interpretation |
|---|---|---|
| CXR | Bilateral diffuse alveolar infiltrates [2][3] | "CXR: pulmonary infiltrates" [2]. Typically bilateral, symmetric, perihilar → peripheral, sparing apices and costophrenic angles. Represents blood filling the alveoli (DAH). May be indistinguishable from pulmonary oedema or infection on CXR alone |
| CT thorax (HRCT) | Diffuse ground-glass opacities ± consolidation in a "crazy paving" pattern | More sensitive than CXR; better delineates DAH vs infection vs fluid overload. "CXR, CT thorax, DLCO for pulmonary involvement if cough ± haemoptysis" [4][6] |
| DLCO (Transfer Factor) | ↑ DLCO | "↑DLCO due to haemoglobin in alveoli" [2]. Paradoxically elevated — free Hb in alveolar spaces avidly binds CO during the test. This is highly specific for alveolar haemorrhage and distinguishes DAH from infection or fluid overload (which ↓ DLCO) |
| USG kidneys | Normal-sized kidneys (unless pre-existing CKD) | Confirms kidneys are not shrunken (small kidneys = chronic irreversible disease → biopsy not indicated). Also checks for obstruction (post-renal AKI) |
Why CXR infiltrates in DAH spare the apices and costophrenic angles? The alveolar haemorrhage follows a gravitational distribution → blood preferentially pools in the dependent (lower and central) lung zones. The apices and extreme bases are relatively spared because capillary hydrostatic pressure and blood flow are lower in these regions.
3.5 Renal Biopsy — The Gold Standard
"The kidney biopsy is the 'gold standard' for the diagnostic evaluation of glomerular diseases" — KDIGO GN Guideline 2021 [5]
"Renal biopsy: necessary for most cases of nephritic syndrome unless very small kidney on USG" [4][6]
| Requirement | Why |
|---|---|
| Normal coagulation parameters (PT, APTT, platelet count) | Renal biopsy is percutaneous with risk of haemorrhage [13] |
| Normal-sized kidneys on USG | Small kidneys indicate chronic irreversible fibrosis — biopsy won't change management and carries unjustified risk |
| Controlled blood pressure | Uncontrolled hypertension increases bleeding risk |
| No active infection at biopsy site | Infection risk |
| Patient consent | Informed consent regarding bleeding, haematoma, rare nephrectomy risk |
Contraindications to percutaneous renal biopsy [14]:
- Bleeding diathesis
- Severe uncontrolled hypertension
- Solitary kidney (relative contraindication)
- Small kidneys (chronic irreversible disease)
- Hydronephrosis
- Renal or perirenal infection
The renal biopsy is examined under three modalities — each provides different information:
| Modality | Findings in Anti-GBM Disease | Significance |
|---|---|---|
| Light Microscopy (LM) | "Cellular crescents (majority), segmental fibrinoid necrosis, GBM breaks" [2] | Shows the severity and chronicity of injury. Cellular crescents = potentially reversible. Fibrous crescents = irreversible. % of glomeruli with crescents determines prognosis |
| Immunofluorescence (IF) | "Characteristic linear IgG/C3 staining along GBM" [2] | PATHOGNOMONIC for anti-GBM disease. This is the single most important finding. "Immunofluorescence pattern most helpful for diagnosis" [4][6] |
| Electron Microscopy (EM) | "GBM disruption w/o significant immune deposits" [2] | Confirms no electron-dense deposits (distinguishes from immune complex GN where subepithelial/subendothelial deposits are seen). Shows GBM breaks and disruption |
| Pattern | Appearance | Mechanism | Disease |
|---|---|---|---|
| Linear | Smooth, continuous, ribbon-like staining along the entire GBM | Antibodies bind directly and uniformly to antigens distributed evenly along the GBM (like paint on a wall) | Anti-GBM disease (Type I) |
| Granular | Lumpy, bumpy, discontinuous deposits | Immune complexes (Ag-Ab aggregates) deposit irregularly in the GBM — like throwing lumps of mud at a wall | Immune complex GN (Type II): lupus, IgAN, PSGN, MPGN |
| Negative/Pauci-immune | No significant immunoglobulin staining | No antibody or immune complex deposition at all — injury is mediated by neutrophils activated by ANCA | ANCA vasculitis (Type III) |
The biopsy is not just diagnostic — it tells you whether treatment is likely to help:
| Biopsy Finding | Prognosis | Treatment Implication |
|---|---|---|
| Predominantly cellular crescents | Potentially reversible | Aggressive treatment indicated — plasma exchange + immunosuppression |
| Mixed cellular/fibrous crescents | Partially reversible | Treatment may salvage some renal function |
| Predominantly fibrous crescents | "Unlikely to respond to immunosuppressive treatment" [1][4] | Aggressive immunosuppression may cause more harm than benefit; consider conservative management |
| > 50% globally sclerosed glomeruli | Irreversible damage | Poor prognosis even with treatment |
| Creatinine > 600 μmol/L at presentation | Very poor prognosis | Most will require permanent dialysis regardless of treatment |
| 100% crescents with need for immediate dialysis | Essentially irreversible | Some centres still offer a short trial of treatment, but renal recovery is extremely rare |
When NOT to Biopsy
In anti-GBM disease specifically, do not delay treatment to wait for biopsy. If anti-GBM serology is positive and the clinical picture fits, start plasma exchange and immunosuppression immediately. Biopsy can be done within the first few days once the patient is stabilised. The biopsy's main role is confirming the diagnosis and determining prognosis (cellular vs fibrous crescents), not deciding whether to start treatment.
When pulmonary involvement is suspected:
| Investigation | Finding | Interpretation |
|---|---|---|
| CXR | Bilateral alveolar infiltrates | Non-specific — can resemble pneumonia or pulmonary oedema |
| CT thorax (HRCT) | Diffuse ground-glass opacities | More sensitive for DAH than CXR |
| DLCO | Elevated ( > 130% predicted) | Pathognomonic of alveolar haemorrhage — free Hb binds CO [2] |
| Bronchoscopy with BAL | Progressively bloodier return on serial aliquots; haemosiderin-laden macrophages (siderophages) | Confirms DAH when diagnosis is uncertain. BAL showing > 20% siderophages is diagnostic of recent alveolar haemorrhage |
| Serial Hb | Falling haemoglobin without obvious external blood loss | Suggests occult pulmonary haemorrhage |
| Iron studies | Iron-deficiency pattern (low ferritin, low serum iron, high TIBC) | "Iron-deficiency anaemia if occult" [2] — iron trapped in lungs as haemosiderin |
| Test | Purpose | When to Order |
|---|---|---|
| ECG | Exclude uraemic pericarditis, hyperkalaemia changes (peaked T waves, widened QRS) | All patients with AKI |
| ABG | Assess degree of metabolic acidosis, oxygenation | If acidotic or respiratory distress |
| Echocardiogram | Exclude IE (if persistent fever + murmur); assess fluid status | "Echocardiogram for IE if persistent fever + murmur" [4][6] |
| Throat swab | Rule out streptococcal infection | "Throat swab for streptococcus infection if recent URTI" [4][6] |
| Investigation | Anti-GBM Disease | ANCA Vasculitis | Lupus Nephritis | PSGN |
|---|---|---|---|---|
| Anti-GBM Ab | +ve | −ve | −ve | −ve |
| ANCA | ± (10–50%) | +ve | −ve | −ve |
| ANA/anti-dsDNA | −ve | −ve | +ve | −ve |
| C3/C4 | Normal | Normal | ↓↓ | ↓ C3 |
| ASOT | −ve | −ve | −ve | +ve |
| IF on biopsy | Linear IgG | Negative | Granular (full house) | Granular (IgG, C3) |
| EM | No deposits | No deposits | Subendothelial deposits | Subepithelial humps |
| DLCO | ↑ (if DAH) | ↑ (if DAH) | Usually normal | Normal |
| CXR | Bilateral infiltrates (DAH) | Infiltrates or cavities | Usually normal | May show fluid overload |
High Yield Summary — Diagnosis of Anti-GBM Disease
-
Diagnosis requires: Positive anti-GBM antibody (ELISA) AND/OR linear IgG on renal biopsy IF, in the context of RPGN ± DAH
-
"The kidney biopsy is the 'gold standard' for diagnostic evaluation of glomerular diseases" (KDIGO 2021 — GC lecture slide) [5]
-
Send anti-GBM, ANCA, ANA, anti-dsDNA, complement, ASOT all simultaneously — this is a time-critical emergency
-
Complement is NORMAL in anti-GBM disease — low complement points to immune complex GN
-
"Immunofluorescence pattern most helpful for diagnosis" [4][6] — Linear IgG = anti-GBM; Granular = immune complex; Negative = pauci-immune
-
EM shows GBM disruption WITHOUT immune deposits — distinguishes from IC-mediated GN
-
DLCO is paradoxically elevated in alveolar haemorrhage — highly specific finding
-
Biopsy prognosticates: Cellular crescents = treatable; fibrous crescents = irreversible
-
Never delay treatment for biopsy if serology is positive and clinical picture fits — "Can give empirical pulse IV methylprednisolone before renal Bx if indicated" [1][4]
-
~5% are seronegative — if clinical suspicion high, proceed to biopsy even with negative ELISA
Active Recall — Diagnosis of Anti-GBM Disease
References
[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 325–326 — Evaluation and RPGN sections) [2] Senior notes: Ryan Ho Urogenital.pdf (p. 67 — Section 3.3.3 Anti-GBM Disease) [3] Senior notes: Maksim Medicine Notes.pdf (p. 231–233 — Anti-GBM disease and RPGN sections) [4] Senior notes: Ryan Ho Fundamentals.pdf (p. 360–361 — Evaluation and RPGN classification) [5] Lecture slides: GC 057. Glomerular and Tubulo-interstitial Diseases and Acute Kidney Injury.pdf (p. 3, 50 — KDIGO guideline and RPGN etiology) [6] Senior notes: Ryan Ho Urogenital.pdf (p. 63 — Evaluation of nephritic syndrome) [12] Senior notes: Maksim Surgery Notes.pdf (p. 307–308 — Haematuria workup) [13] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p. 1734 — Case study, renal biopsy requirements) [14] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (p. 770 — Renal biopsy contraindications)
Management of Anti-GBM Disease
Before diving into specifics, let's understand why anti-GBM disease is treated the way it is. The treatment logic flows directly from the pathophysiology:
| Pathological Process | Treatment Target | Treatment Modality |
|---|---|---|
| Circulating anti-GBM antibodies in the blood | Remove them physically | Plasma exchange (plasmapheresis) |
| Ongoing antibody production by B cells/plasma cells | Suppress new antibody synthesis | Cyclophosphamide or rituximab |
| Inflammatory damage from antibodies already deposited in GBM (complement activation, neutrophil recruitment, crescent formation) | Suppress the inflammatory response | IV pulse methylprednisolone → oral prednisolone |
| AKI complications (hyperkalaemia, fluid overload, acidosis, uraemia) | Supportive care ± renal replacement therapy | Dialysis, electrolyte management, fluid balance |
| Pulmonary haemorrhage (life-threatening) | Stop the bleeding + support oxygenation | Plasma exchange + immunosuppression + respiratory support |
The treatment is therefore a three-pronged attack: remove existing antibodies (plasma exchange), prevent new antibody production (cyclophosphamide), and dampen inflammation from already-deposited antibodies (corticosteroids).
Anti-GBM disease management: "IV pulse MP × 3 days + oral prednisolone ± cyclophosphamide / IV rituximab ± plasma exchange" [3]
"Plasma exchange for fulminant MPA / GPA or Goodpasture's syndrome" [3]
Why Is Plasma Exchange So Critical in Anti-GBM Disease?
Unlike ANCA vasculitis (where the pathology is primarily cell-mediated via neutrophil activation), anti-GBM disease is a directly antibody-mediated disease. The circulating IgG autoantibody is the primary pathogenic agent. Plasma exchange physically removes these antibodies from the circulation faster than the body can produce them. Without plasma exchange, even immunosuppression alone may be too slow — by the time cyclophosphamide suppresses antibody production (takes 1–2 weeks to work), the kidneys may already be destroyed.
This is why plasma exchange is considered essential in anti-GBM disease but only used in severe/refractory ANCA vasculitis.
3. Treatment Modalities — Detailed Breakdown
What it is: A procedure that physically separates the patient's plasma (containing the pathogenic anti-GBM antibodies) from the blood cells, discards the plasma, and replaces it with albumin solution or fresh frozen plasma (FFP).
- "Plasma" = the liquid portion of blood containing proteins, antibodies, clotting factors
- "Pheresis" (from Greek ἀφαίρεσις) = removal, taking away
- So plasmapheresis = "taking away the plasma"
How it works mechanistically:
- Blood is drawn from the patient via a large-bore venous catheter (usually a Quinton catheter in the internal jugular or femoral vein)
- Blood passes through a centrifuge or membrane filter that separates plasma from blood cells
- The plasma (containing anti-GBM IgG) is discarded
- Blood cells are returned to the patient mixed with replacement fluid (5% albumin ± FFP)
- Each session removes approximately 60% of circulating IgG
- Over 2–3 weeks of daily/alternate-day sessions, the antibody titre drops dramatically
| Parameter | Details |
|---|---|
| Regimen | Daily or alternate-day, 4-litre exchanges × 2–3 weeks [2] |
| Replacement fluid | Albumin (5%) + FFP as replacement fluid [2]. FFP is used if there is active pulmonary haemorrhage (contains clotting factors to help stop bleeding) or pre-biopsy (to maintain coagulation) |
| Duration | Typically 14 sessions over 2–3 weeks, or until anti-GBM titres are undetectable |
| Monitoring | "Monitor anti-GBM titres Q1–2w until negative on two occasions" [2] |
Indications:
- All patients with anti-GBM disease who have pulmonary haemorrhage [2]
- Non-dialysis-dependent renal involvement [2]
- Critical for antibody removal — the faster you remove antibodies, the less GBM destruction occurs
Contraindications/Cautions:
| Contraindication | Reason |
|---|---|
| Haemodynamic instability (severe septic shock) | Plasma exchange requires extracorporeal circulation and can worsen hypotension |
| Active bleeding (relative) | Removal of clotting factors; mitigated by using FFP as replacement |
| Allergy to albumin or FFP | Replacement fluid reaction |
| Difficult vascular access | Requires large-bore central venous catheter |
Complications of plasma exchange:
| Complication | Mechanism |
|---|---|
| Hypotension | Fluid shifts during procedure |
| Hypocalcaemia (paraesthesias, muscle cramps) | Citrate anticoagulant used in the circuit chelates calcium |
| Coagulopathy | Removal of clotting factors (especially fibrinogen); mitigated by FFP replacement |
| Infection risk | Central line-related infections |
| Allergic reactions | To replacement albumin or FFP |
Why Albumin vs FFP as Replacement Fluid?
- 5% Albumin is preferred as the default replacement because it is safe, well-tolerated, and does not carry infection risk
- FFP is added or substituted when:
- The patient has active pulmonary haemorrhage (FFP replaces clotting factors removed during plasma exchange, helping to control bleeding)
- The patient is about to undergo renal biopsy (need intact coagulation)
- There is laboratory evidence of significant coagulopathy
"Plasma exchange to remove circulating antibodies — Regimen: daily or alternate-day 4 litre exchanges × 2-3 weeks + albumin/FFP as replacement fluid" [2]
Purpose: Suppress the inflammatory cascade triggered by antibodies already deposited in the GBM. Even after plasma exchange removes circulating antibodies, the antibodies already bound to the GBM continue to activate complement and recruit inflammatory cells → corticosteroids dampen this ongoing inflammation.
Phase 1 — Induction (Pulse IV Methylprednisolone):
| Parameter | Details |
|---|---|
| Drug | IV methylprednisolone (MP) |
| Dose | 500–1000 mg/day IV × 3 days ("pulse") [2][3] |
| Why "pulse"? | Ultra-high dose achieves rapid, potent immunosuppression — suppresses NF-κB transcription factor within hours, blocking production of IL-1, IL-6, TNF-α, and other pro-inflammatory cytokines. Also induces lymphocyte apoptosis |
| Timing | "Can give empirical pulse IV methylprednisolone before renal Bx if indicated" [1][4] — start immediately, do not wait for biopsy |
"IV pulse MP × 3 days" [3]
Phase 2 — Maintenance (Oral Prednisolone):
| Parameter | Details |
|---|---|
| Drug | Oral prednisolone |
| Starting dose | 1 mg/kg/day (max 60–80 mg/day) |
| Taper | Gradual taper after remission is achieved (anti-GBM titres negative, creatinine stabilised). Typically reduced over 6–9 months |
| Duration | Total corticosteroid duration usually 6–9 months [2] |
"Followed by oral prednisolone (tapered after remission)" [2]
Side effects of corticosteroids (important for exam — common SAQ topic):
| System | Side Effects | Mechanism |
|---|---|---|
| Metabolic | Hyperglycaemia, diabetes | ↑ Hepatic gluconeogenesis, ↓ peripheral glucose uptake |
| Musculoskeletal | Osteoporosis, avascular necrosis, proximal myopathy | ↓ Osteoblast activity, ↑ osteoclast activity; ↓ calcium absorption |
| GI | Peptic ulcer, GI bleeding | ↓ Prostaglandin-mediated mucosal protection |
| Infection | Opportunistic infections (PJP, TB, fungal) | Immunosuppression — T cell suppression, ↓ macrophage function |
| CVS | Hypertension, fluid retention | Mineralocorticoid effect (Na/water retention) |
| Psychiatric | Insomnia, psychosis, mood changes | CNS effects |
| Adrenal | Adrenal suppression on withdrawal | Exogenous steroid suppresses HPA axis via negative feedback |
| Other | Cushingoid facies, striae, weight gain, cataracts, glaucoma | Multiple mechanisms |
Prophylaxis during steroid therapy:
- PPI (omeprazole/pantoprazole) for gastroprotection
- Calcium + Vitamin D ± bisphosphonate for osteoporosis prevention
- PJP prophylaxis (co-trimoxazole) when on high-dose steroids + cyclophosphamide
- Blood glucose monitoring (steroid-induced diabetes)
Purpose: Suppress ongoing autoantibody production by killing rapidly dividing immune cells (particularly B lymphocytes that differentiate into antibody-producing plasma cells).
- "Cyclo" = cyclic; "phosph" = phosphorus-containing; "amide" = nitrogen-containing group
- It is a nitrogen mustard alkylating agent — cross-links DNA strands, preventing cell division
- Works best against rapidly dividing cells → lymphocytes, particularly B cells
| Parameter | Details |
|---|---|
| Route | Oral cyclophosphamide is traditional [2]; some centres use IV pulse cyclophosphamide |
| Oral dose | 2–3 mg/kg/day (rounded down to nearest 50 mg), adjusted for age and renal function |
| IV dose | 15 mg/kg (max 1.2 g) every 2 weeks × 3 doses, then every 3 weeks × 3 doses (Euro-lupus style) |
| Duration | Usually 2–3 months during induction phase [2] |
"Oral cyclophosphamide to suppress further antibody synthesis" [2]
"± cyclophosphamide / IV rituximab" [3]
Indications:
- All patients receiving treatment for anti-GBM disease (standard component of triple therapy)
Contraindications:
| Contraindication | Reason |
|---|---|
| Active infection | Severe immunosuppression → overwhelming sepsis |
| Pregnancy (Category D) | Teratogenic — causes congenital malformations |
| Severe leucopaenia (WBC < 3.0 × 10⁹/L) | Risk of life-threatening neutropaenic sepsis |
| Bladder outflow obstruction | Risk of accumulation of toxic metabolite (acrolein) in bladder |
Side effects:
| Side Effect | Mechanism | Prevention |
|---|---|---|
| Bone marrow suppression (leucopaenia, anaemia, thrombocytopaenia) | Alkylating agent kills rapidly dividing haematopoietic precursors | Monitor FBC weekly; dose-adjust |
| Infection (PJP, herpes, bacterial sepsis) | Lymphocyte depletion → immunosuppression | PJP prophylaxis (co-trimoxazole); monitor for infection |
| Haemorrhagic cystitis | Toxic metabolite acrolein excreted in urine → direct bladder mucosal damage | Mesna (2-mercaptoethane sulfonate sodium) binds acrolein in urine; adequate hydration |
| Bladder carcinoma (long-term risk) | Chronic acrolein exposure → urothelial carcinogenesis | Limit cumulative dose; mesna; adequate hydration |
| Gonadal toxicity (infertility) | Alkylation of rapidly dividing germ cells | Discuss fertility preservation (sperm banking, oocyte cryopreservation) BEFORE starting treatment |
| Nausea/vomiting | Direct GI mucosal irritation + CTZ stimulation | Anti-emetics (ondansetron) |
| Alopecia | Damage to rapidly dividing hair follicle cells | Usually reversible on cessation |
| Secondary malignancy (lymphoma, leukaemia) | DNA damage in haematopoietic stem cells | Limit cumulative dose |
Purpose: Selectively depletes CD20+ B lymphocytes → eliminates the cells that differentiate into antibody-producing plasma cells. Increasingly used as an alternative to cyclophosphamide, particularly in younger patients (avoids gonadal toxicity) and those intolerant to cyclophosphamide.
- "Ri-tuxi-mab": "-mab" = monoclonal antibody; "tu" = tumour-targeted (originally developed for B-cell lymphoma); "xi" = chimeric (mouse/human)
- It is a chimeric anti-CD20 monoclonal antibody
| Parameter | Details |
|---|---|
| Dose | 375 mg/m² IV weekly × 4 weeks, or 1000 mg IV on day 1 and day 15 |
| Mechanism | Binds CD20 on B cell surface → antibody-dependent cellular cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and direct apoptosis → B cell depletion |
| Onset | B cells depleted within days; antibody titres fall over weeks |
| Duration of effect | B cell depletion lasts 6–12 months |
"± cyclophosphamide / IV rituximab" [3]
Indications for rituximab over cyclophosphamide:
- Young patients of reproductive age (fertility preservation)
- Previous cyclophosphamide toxicity or intolerance
- Double-positive disease (anti-GBM + ANCA) — the ANCA component may relapse, and rituximab is effective for ANCA maintenance
- Some centres now use rituximab as first-line instead of cyclophosphamide based on ANCA vasculitis trial data (RAVE, RITUXVAS), though specific anti-GBM RCT data is limited
Contraindications:
| Contraindication | Reason |
|---|---|
| Active severe infection (especially HBV) | Risk of HBV reactivation → fulminant hepatitis. Screen HBV before use |
| Severe heart failure (NYHA IV) | Infusion-related cytokine release can worsen cardiac function |
| Previous severe infusion reaction to rituximab | Anaphylaxis risk |
Side effects:
| Side Effect | Mechanism |
|---|---|
| Infusion reactions (fever, rigors, hypotension, bronchospasm) | Cytokine release from B cell lysis — most common with first infusion. Pre-medicate with paracetamol, antihistamine, and IV methylprednisolone |
| HBV reactivation | Loss of immune surveillance of latent HBV — always screen HBsAg and anti-HBc before starting |
| Progressive multifocal leukoencephalopathy (PML) | JC virus reactivation due to prolonged B cell depletion — very rare but fatal |
| Hypogammaglobulinaemia | Sustained B cell depletion → ↓ immunoglobulin production → recurrent infections |
| Late-onset neutropaenia | Mechanism unclear; usually self-limiting |
3.5 Supportive and Adjunctive Management
| Complication | Management | Rationale |
|---|---|---|
| Hyperkalaemia | IV calcium gluconate (cardioprotection), insulin-dextrose (intracellular K shift), salbutamol nebuliser, sodium bicarbonate if acidotic, potassium binders (sodium polystyrene sulfonate), dialysis if refractory [15] | K > 6.0–6.5 mmol/L is life-threatening → cardiac arrhythmias |
| Fluid overload / pulmonary oedema | Fluid restriction, IV loop diuretics (furosemide), dialysis if refractory [15] | ↓ GFR → Na/water retention → pulmonary oedema → respiratory failure |
| Metabolic acidosis | IV sodium bicarbonate (if pH < 7.1), dialysis [15] | ↓ GFR → impaired H+ excretion → acidosis |
| Uraemia (pericarditis, encephalopathy) | Dialysis [15] | Uraemic toxin accumulation causing organ damage — dialysis is the only definitive treatment |
"Indications for dialysis: Acidosis, Electrolyte imbalance, Intoxication, Overload, Uraemia" — mnemonic: AEIOU [15]
| Measure | Details |
|---|---|
| Airway management | Intubation and mechanical ventilation if severe DAH with respiratory failure |
| Plasma exchange with FFP | FFP replaces clotting factors removed during exchange → helps control bleeding |
| Oxygen therapy | Maintain SpO₂ > 94% |
| Avoid fluid overload | Excess IV fluid worsens alveolar haemorrhage by increasing hydrostatic pressure across pulmonary capillaries |
| Smoking cessation | Absolute — smoking perpetuates alveolar basement membrane exposure |
| Transfusion | Packed RBCs if Hb < 70 g/L or symptomatic anaemia |
| Measure | Rationale |
|---|---|
| Blood pressure control | ↓ GFR activates RAAS → hypertension → further renal damage. Use non-ACEI/ARB agents acutely (risk of worsening AKI/hyperkalaemia) |
| Infection prophylaxis | Co-trimoxazole for PJP prophylaxis (on cyclophosphamide + high-dose steroids); vaccination catch-up when immunosuppression tapered |
| DVT prophylaxis | Nephrotic-range proteinuria (if present) → hypercoagulable state; also immobilisation risk |
| Nutritional support | Adequate caloric intake; may need renal diet (low K, low phosphate) if on dialysis |
| Psychological support | Young patient facing potential lifelong dialysis — significant psychological burden |
"Indication: usually limited to those with pulmonary haemorrhage (may be fatal) or non-dialysis dependent renal involvement (those requiring RRT are not likely to respond)" [2]
| Scenario | Recommended Approach | Rationale |
|---|---|---|
| RPGN + DAH (Goodpasture's syndrome) | Full triple therapy: Plasma exchange (daily × 2–3 weeks) + IV pulse MP × 3d → oral pred + cyclophosphamide/rituximab | Life-threatening DAH mandates immediate aggressive treatment regardless of renal prognosis |
| RPGN, non-dialysis-dependent (Cr elevated but not on dialysis) | Full triple therapy as above | Best chance of renal recovery; early treatment critical — every day of delay worsens prognosis |
| RPGN, dialysis-dependent at presentation, predominantly CELLULAR crescents on biopsy | Trial of triple therapy for 2–3 weeks → reassess for renal recovery | Some patients with cellular crescents may recover renal function if treated early |
| RPGN, dialysis-dependent, predominantly FIBROUS crescents or 100% crescents | Conservative management: dialysis ± transplant planning; avoid immunosuppression toxicity | "Fibrous crescents — unlikely to respond to immunosuppressive treatment" [1][4]. Aggressive treatment exposes patient to toxicity without realistic benefit |
| Double-positive (anti-GBM + ANCA) | Triple therapy as for anti-GBM + consider rituximab for ANCA maintenance | ANCA component may relapse; rituximab effective for ANCA maintenance. "ANCA: may be present in 10-50% anti-GBM pt, indicates better response to Tx" [2] |
The Dialysis Dilemma
A common exam pitfall: "Should you treat a patient who already needs dialysis at presentation?"
The answer is nuanced:
- If the patient has pulmonary haemorrhage → YES, always treat (DAH can be fatal)
- If the patient is dialysis-dependent without DAH → biopsy first:
- Cellular crescents → trial of treatment (some may recover)
- Fibrous crescents / extensive sclerosis → treatment unlikely to help; focus on dialysis and transplant planning
- Creatinine > 600 μmol/L requiring immediate dialysis → very poor renal prognosis; most will remain dialysis-dependent
This is why the renal biopsy is prognostically critical — it determines whether aggressive (and toxic) immunosuppression is justified.
| Parameter | Frequency | Target |
|---|---|---|
| Anti-GBM antibody titre | Every 1–2 weeks [2] | Negative on two consecutive occasions [2] — indicates successful antibody removal |
| RFT (creatinine, eGFR, K+) | Daily during acute phase, then weekly | Stabilisation or improvement in creatinine |
| FBC (WBC, Hb, platelets) | Weekly (during cyclophosphamide) | WBC > 3.0 × 10⁹/L (dose-reduce cyclophosphamide if falling) |
| CXR | As clinically indicated | Resolution of pulmonary infiltrates |
| DLCO | As clinically indicated | Normalisation (falling DLCO = resolving DAH) |
| Urinalysis | Weekly | Clearing of haematuria, ↓ proteinuria |
| Blood glucose | Daily during pulse steroids, then regularly | Steroid-induced hyperglycaemia |
"Duration: usually induce remission within 2–3w, then continue maintenance for 6–9w" [2]
"Prognosis: autoantibody production is transient → self-limiting if can tide over crisis" [2]
| Factor | Details |
|---|---|
| 5-year renal survival | 34% [2] (i.e., 66% on dialysis or transplanted) |
| 5-year patient survival | 83% [2] |
| Relapse rate | < 2% [2] — remarkably low. "Probably related to induction of peripheral tolerance vs Goodpasture Ag" [2] |
| Most important prognostic factor | "Degree of renal impairment at diagnosis — those who require immediate dialysis are unlikely to be dialysis-free in long term" [2] |
| Disease is self-limiting | Antibody production is transient (weeks to months), unlike ANCA vasculitis which relapses. If the patient can survive the acute crisis (tide over the storm), the disease burns itself out |
Why is anti-GBM disease self-limiting? This is unique among autoimmune diseases. The autoimmune response against the Goodpasture antigen is typically monophasic — the immune system seems to develop tolerance to the antigen after the initial flare. The mechanisms are not fully understood but may involve:
- Deletion/anergy of autoreactive T cells after the antigen is destroyed
- Regulatory T cell expansion
- Immune complex-mediated feedback inhibition of B cell activation
This self-limiting nature has two important implications:
- Low relapse rate — unlike SLE or ANCA vasculitis, you don't need long-term maintenance immunosuppression
- Renal transplantation is feasible — but wait until anti-GBM titres are negative for ≥ 6 months before transplant to avoid recurrence in the graft
| Consideration | Details |
|---|---|
| Timing | Wait until anti-GBM antibodies are undetectable for ≥ 6 months before transplant |
| Recurrence risk | Very low ( < 5%) if antibodies are negative at time of transplant |
| Special situation: Alport syndrome | Patients with Alport syndrome who develop ESRD and receive a transplant may develop de novo anti-GBM disease against the normal α3(IV) collagen in the graft (5–10% of Alport transplant recipients) [2] |
| Phase | Duration | Treatment |
|---|---|---|
| Acute induction | Days 1–3 | IV pulse methylprednisolone 500–1000 mg/day × 3 days [2][3] |
| Plasma exchange | 2–3 weeks | Daily or alternate-day 4L exchanges × 14 sessions [2] |
| Immunosuppression | Starts day 1, continues 2–3 months | Oral cyclophosphamide 2–3 mg/kg/day OR IV rituximab [2][3] |
| Oral steroids | Starts after pulse MP, tapers over 6–9 months | Oral prednisolone 1 mg/kg/day [2][3], taper after remission |
| Monitoring | Throughout | Anti-GBM titres Q1–2 weeks until negative × 2 [2] |
| Total treatment duration | 6–9 months | Then stop — disease is self-limiting; no long-term maintenance needed [2] |
High Yield Summary — Management of Anti-GBM Disease
-
Triple therapy: Plasma exchange + corticosteroids + cyclophosphamide (or rituximab) — targets three pathological processes: remove antibodies, suppress inflammation, prevent new antibody synthesis
-
"IV pulse MP × 3 days + oral prednisolone ± cyclophosphamide / IV rituximab ± plasma exchange" [3]
-
Plasma exchange is ESSENTIAL in anti-GBM disease (not optional like in most ANCA vasculitis) — physically removes pathogenic IgG
-
Start treatment IMMEDIATELY — "Can give empirical pulse IV methylprednisolone before renal Bx if indicated" [1][4]
-
Treatment indication: Pulmonary haemorrhage (always treat) or non-dialysis-dependent renal disease. Dialysis-dependent patients with fibrous crescents unlikely to benefit
-
"Most important prognostic factor is degree of renal impairment at diagnosis" [2]
-
Disease is self-limiting — antibody production is transient; relapse rate < 2% [2]; no long-term maintenance needed
-
"Monitor anti-GBM titres Q1–2w until negative on two occasions" [2]
-
5-year survival: Patient 83%, renal 34% [2]
-
Transplantation: Wait until anti-GBM negative ≥ 6 months; Alport patients risk de novo anti-GBM disease post-transplant
Active Recall — Management of Anti-GBM Disease
References
[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 326 — RPGN management) [2] Senior notes: Ryan Ho Urogenital.pdf (p. 68 — Anti-GBM management, prognosis) [3] Senior notes: Maksim Medicine Notes.pdf (p. 231–233 — Anti-GBM management table, RPGN management) [4] Senior notes: Ryan Ho Fundamentals.pdf (p. 361 — RPGN management) [15] Senior notes: Ryan Ho Critical Care.pdf (p. 26 — AKI management, dialysis indications)
Complications of Anti-GBM Disease
Complications of anti-GBM disease can be divided into disease-related complications (resulting from the disease process itself) and treatment-related complications (resulting from the immunosuppressive therapy and plasma exchange). Both are clinically important and commonly examined.
1. Disease-Related Complications
ESRD is the single most important complication and the defining adverse outcome of anti-GBM disease.
| Aspect | Details |
|---|---|
| Frequency | 5-year renal survival is only 34% [2] — meaning ~66% of patients will develop ESRD within 5 years despite treatment |
| Time course | "Rapidly declining renal function leading to ESRD in days to weeks" [4] if untreated; even with treatment, many present too late for renal salvage |
| Mechanism | Anti-GBM antibodies → GBM destruction → crescents compress and obliterate glomerular capillary tufts → progressive irreversible nephron loss → GFR falls below 15 mL/min → ESRD. "Fibrous crescents — unlikely to respond to immunosuppressive treatment" [1][4] — once fibrosis replaces cellular crescents, the damage is permanent |
| Key prognostic factor | "Most important prognostic factor is degree of renal impairment at diagnosis — those who require immediate dialysis are unlikely to be dialysis-free in long term" [2] |
Why is the renal prognosis so poor? Several factors conspire:
- Anti-GBM disease presents explosively — by the time the patient is symptomatic (haematuria, oliguria, uraemia), extensive crescentic destruction has already occurred
- The damage accelerates: each destroyed glomerulus shifts the filtration burden to remaining glomeruli → hyperfiltration injury → secondary FSGS and tubulointerstitial fibrosis → further nephron loss (the "common pathway" to ESRD that applies to all renal pathologies)
- Once crescents become fibrous, they are irreversible regardless of treatment intensity
Consequences of ESRD:
| Consequence | Mechanism | Management |
|---|---|---|
| Need for chronic dialysis (haemodialysis or peritoneal dialysis) | GFR < 15 mL/min → unable to maintain homeostasis | Long-term renal replacement therapy |
| Renal transplantation | Preferred over dialysis for survival and quality of life | Wait until anti-GBM Ab negative ≥ 6 months [2] |
| Complications of CKD (anaemia, renal osteodystrophy, cardiovascular disease, malnutrition) | Loss of EPO production; disordered phosphate/calcium/PTH metabolism; accelerated atherosclerosis; uraemic toxin accumulation | EPO, phosphate binders, vitamin D, statins, dietary management |
DAH is the complication that can kill the patient acutely, unlike ESRD which is manageable with dialysis.
| Aspect | Details |
|---|---|
| Frequency | 40–60% of anti-GBM disease patients [2] |
| Mechanism | Anti-GBM antibodies bind the alveolar basement membrane (same α3(IV) collagen) → pulmonary capillaritis → rupture of alveolar capillaries → blood floods the alveolar spaces → impaired gas exchange → hypoxaemia → respiratory failure |
| Mortality | Before modern treatment: ~50% mortality from massive pulmonary haemorrhage. With current triple therapy + plasma exchange: significantly reduced but still the major cause of early death |
| Risk factor | "Those with lung involvement more commonly a/w underlying pulmonary injury, eg. smoking, infection" [2] — smoking is virtually always present in patients with DAH |
Complications of DAH itself:
| Complication of DAH | Mechanism |
|---|---|
| Acute respiratory failure | Massive alveolar flooding → V/Q mismatch → hypoxaemia; may require intubation and mechanical ventilation |
| Iron-deficiency anaemia | "Iron-deficiency anaemia if occult" [2] — chronic/recurrent pulmonary haemorrhage traps iron as haemosiderin in alveolar macrophages → systemic iron depletion → microcytic hypochromic anaemia |
| Pulmonary fibrosis (late) | Repeated episodes of DAH → organising pneumonia → interstitial fibrosis → restrictive lung disease |
| Haemorrhagic shock (rare, massive DAH) | Catastrophic blood loss into the lungs → hypovolaemic shock |
| Aspiration / airway obstruction | Blood clots in the airways → bronchial obstruction → atelectasis or aspiration pneumonia |
DAH vs Pulmonary Oedema — The Diagnostic Trap
Both DAH and pulmonary oedema can present with bilateral CXR infiltrates, crackles, and dyspnoea in a patient with AKI. The key distinguisher:
- DAH: ↑DLCO (Hb in alveoli binds CO), haemoptysis, falling Hb without obvious external bleeding, haemosiderin-laden macrophages on BAL
- Pulmonary oedema: ↓DLCO (fluid in interstitium impairs diffusion), no haemoptysis, responds to diuretics, cardiomegaly on CXR
Getting this wrong can be fatal — pulmonary oedema needs diuresis/ultrafiltration, while DAH needs plasma exchange and immunosuppression.
The rapid loss of GFR in RPGN produces several life-threatening metabolic emergencies [15]:
| Complication | Mechanism | Clinical Manifestation | Management |
|---|---|---|---|
| Hyperkalaemia | ↓ GFR → ↓ renal K+ excretion → K+ accumulates in blood | Arrhythmia, weakness, cardiac arrest (peaked T waves, widened QRS, sine wave on ECG) | IV calcium gluconate (cardioprotection), insulin-dextrose, salbutamol, polystyrene sulfonate, dialysis [15] |
| Metabolic acidosis | ↓ GFR → ↓ H+ excretion + ↓ HCO₃⁻ regeneration → accumulation of H+ ions (raised anion gap metabolic acidosis) | Kussmaul's breathing (deep, laboured breathing — the body's attempt to blow off CO₂ to compensate for the acidosis); confusion; cardiovascular depression | IV sodium bicarbonate, dialysis [15] |
| Fluid overload | ↓ GFR → ↓ Na/water excretion → positive fluid balance → volume expansion | Peripheral oedema, hypertension, pulmonary oedema (crackles, orthopnoea, raised JVP) | IV loop diuretics (furosemide), fluid restriction, dialysis [15] |
| Uraemia | Accumulation of uraemic toxins (urea, creatinine, indoxyl sulphate, p-cresol) → multi-organ toxicity | Uraemic pericarditis (friction rub — the indication for urgent dialysis), uraemic encephalopathy (confusion, seizures, asterixis), uraemic neuropathy | Dialysis [15] |
| Hypertension | Volume expansion + RAAS activation (ischaemic glomeruli → JGA senses ↓ perfusion → renin release) | ↑ BP → further glomerular damage (vicious cycle); risk of hypertensive encephalopathy, aortic dissection, stroke | Antihypertensives; diuresis; dialysis |
"Management of life-threatening complications: Fluid overload — Mx: IV loop diuretics, dialysis; Hyperkalaemia — Mx: IV Ca, NaHCO₃ infusion, dextrose/insulin drip, PO polysulphonate, dialysis; Metabolic acidosis — Mx: IV bicarbonate, dialysis" [15]
Indications for dialysis (AEIOU): Acidosis, Electrolyte imbalance (hyperK), Intoxication, Overload (fluid), Uraemia [15]
| Complication | Mechanism |
|---|---|
| Deep vein thrombosis / pulmonary embolism | Patients with significant proteinuria (even sub-nephrotic) lose anticoagulant proteins (antithrombin III, protein C, protein S) in the urine while the liver compensatorily increases synthesis of procoagulant factors (fibrinogen, factors V and VIII) → hypercoagulable state [16]. Additionally: immobilisation during acute illness, central venous catheters for plasma exchange, and dehydration all increase risk |
| Renal vein thrombosis (rare in anti-GBM, more common in membranous nephropathy) | Same hypercoagulable mechanism; renal vein thrombosis may worsen renal function acutely |
"Hypercoagulability by compensatory production of clotting factors by liver" → "Doppler USG, CT angiography; if AKI: thrombolysis ± embolectomy; if non-AKI: LMWH/UFH → warfarin for minimum 6–12 months while still nephrotic" [16]
| Mechanism | Consequence |
|---|---|
| Urinary loss of immunoglobulins (IgG) through the damaged GBM | ↓ Humoral immunity → increased susceptibility to encapsulated bacteria (pneumococcus, H. influenzae) |
| Uraemia itself is immunosuppressive | ↓ T cell function, ↓ neutrophil chemotaxis → impaired host defence even before immunosuppressive treatment starts |
| Aspect | Details |
|---|---|
| Relapse rate | "Rarely relapse ( < 2%), probably related to induction of peripheral tolerance vs Goodpasture Ag" [2] |
| Post-transplant recurrence | If transplanted while anti-GBM Ab still detectable → antibodies attack the new kidney's GBM → de novo crescentic GN in the graft. This is why transplantation is delayed until anti-GBM negative ≥ 6 months [2] |
| Alport syndrome post-transplant | "Post-transplant anti-GBM disease: can occur in 5–10% of renal transplant recipients in underlying Alport syndrome" [2] — Alport patients have never been exposed to normal α3(IV) collagen, so the transplanted kidney introduces a "foreign" antigen → de novo anti-GBM antibody production |
2. Treatment-Related Complications
The aggressive immunosuppressive regimen (corticosteroids + cyclophosphamide + plasma exchange) carries its own significant burden of complications. In a disease with only 34% 5-year renal survival, treatment toxicity is a major consideration — especially in patients unlikely to benefit (fibrous crescents, dialysis-dependent at presentation).
| System | Complication | Mechanism |
|---|---|---|
| Infection | Opportunistic infections (Pneumocystis jirovecii pneumonia (PJP), oral candidiasis, herpes zoster reactivation, TB reactivation) | Suppression of T cell-mediated immunity + ↓ macrophage function |
| Metabolic | Steroid-induced diabetes / hyperglycaemia | ↑ Hepatic gluconeogenesis + ↓ peripheral glucose uptake + ↓ insulin sensitivity |
| Musculoskeletal | Osteoporosis, avascular necrosis of femoral head | ↓ Osteoblast activity + ↑ osteoclast activity + ↓ intestinal calcium absorption |
| GI | Peptic ulcer disease, GI bleeding | ↓ Prostaglandin-mediated gastric mucosal protection |
| Psychiatric | Insomnia, psychosis, mood disturbance | Direct CNS glucocorticoid receptor effects |
| Cardiovascular | Hypertension, fluid retention | Mineralocorticoid effect (Na+/water retention) |
| Adrenal | Adrenal insufficiency on withdrawal | Chronic exogenous steroid suppresses HPA axis via negative feedback → adrenal atrophy → cannot mount appropriate cortisol response when steroid tapered/stopped |
| Cosmetic | Cushingoid facies, truncal obesity, striae, acne, hirsutism | Redistribution of fat to central areas; collagen breakdown in skin |
Prophylaxis:
- PPI for gastroprotection
- Calcium + vitamin D ± bisphosphonate for bone protection
- Co-trimoxazole for PJP prophylaxis (when on cyclophosphamide + high-dose steroids)
- Blood glucose monitoring
| Complication | Mechanism | Prevention/Monitoring |
|---|---|---|
| Bone marrow suppression (leucopaenia → neutropaenic sepsis) | Alkylating agent kills rapidly dividing haematopoietic precursors | FBC weekly; nadir usually at 7–14 days; dose-reduce if WBC < 3.0 |
| Haemorrhagic cystitis | Toxic metabolite acrolein excreted in urine → direct urothelial damage | Adequate hydration; mesna (binds acrolein); monitor for haematuria |
| Gonadal toxicity (infertility) | Alkylation of rapidly dividing germ cells (oocytes, spermatogonia) | Discuss fertility preservation BEFORE starting (sperm banking, oocyte cryopreservation) |
| Bladder carcinoma (long-term) | Chronic acrolein exposure → urothelial carcinogenesis | Limit cumulative dose; long-term surveillance urinalysis |
| Secondary malignancy (lymphoma, leukaemia, skin cancer) | DNA damage in haematopoietic stem cells + carcinogenic DNA cross-linking | Limit cumulative dose; long-term cancer surveillance |
| Nausea/vomiting | CTZ stimulation + direct GI mucosal irritation | Anti-emetics (ondansetron) |
| Alopecia | Damage to rapidly dividing hair follicle matrix cells | Usually reversible on cessation |
| Teratogenicity | DNA alkylation in developing fetus | Absolute contraindication in pregnancy; effective contraception mandatory |
| Complication | Mechanism |
|---|---|
| Infusion reactions (fever, rigors, urticaria, bronchospasm, hypotension) | Cytokine release from B cell lysis — most severe with first infusion when B cell load is highest |
| HBV reactivation → fulminant hepatitis | Loss of B cell-mediated immune surveillance over latent HBV → viral replication → hepatic necrosis. Always screen HBsAg and anti-HBc before starting; give antiviral prophylaxis if positive |
| Progressive multifocal leukoencephalopathy (PML) | JC virus reactivation due to profound immunosuppression from prolonged B cell depletion — extremely rare but fatal |
| Hypogammaglobulinaemia | Sustained B cell depletion → ↓ immunoglobulin synthesis → recurrent sinopulmonary infections |
| Late-onset neutropaenia | Mechanism incompletely understood; occurs weeks to months after rituximab; usually self-limiting |
| Complication | Mechanism | Prevention |
|---|---|---|
| Hypotension | Large-volume extracorporeal fluid shifts | Slow exchange rate; IV fluid boluses |
| Hypocalcaemia (paraesthesias, tetany, QT prolongation) | Citrate anticoagulant chelates calcium | Monitor ionised calcium; IV calcium gluconate supplementation |
| Coagulopathy / bleeding | Removal of clotting factors (fibrinogen, factor V, factor VIII) | Use FFP as replacement fluid when bleeding risk high; check coagulation profile after sessions |
| Central line-related infection (catheter-related bloodstream infection, CRBSI) | Large-bore central venous catheter required for vascular access | Strict aseptic technique; monitor for line sepsis; remove catheter when exchange course completed |
| Allergic reactions | To albumin or FFP replacement fluids | Pre-medication; monitor during infusion |
| Electrolyte disturbances | Removal and replacement of plasma alters ionic composition | Monitor electrolytes post-session |
| Increased drug clearance | Removal of protein-bound drugs (including therapeutic antibodies and some anticonvulsants) | Time drug dosing after (not before) plasma exchange sessions — especially important for rituximab |
Drug Timing with Plasma Exchange
Plasma exchange removes large protein-bound molecules. If you give rituximab (a large IgG1 monoclonal antibody) and then perform plasma exchange the same day, you will physically remove the rituximab you just administered — wasting an expensive drug and losing its therapeutic effect. Always schedule drug infusions AFTER plasma exchange sessions, not before.
| Complication | Mechanism | Time Frame |
|---|---|---|
| CKD progression to ESRD | Even patients who initially recover some renal function may slowly progress due to secondary FSGS and tubulointerstitial fibrosis from nephron loss (the common final pathway) | Months to years |
| Cardiovascular disease | CKD is a major cardiovascular risk factor (accelerated atherosclerosis, LVH, vascular calcification); steroid use adds metabolic syndrome; persistent proteinuria worsens dyslipidaemia | Years |
| Pulmonary fibrosis (post-DAH) | Repeated alveolar haemorrhage → organising pneumonia → interstitial fibrosis → restrictive defect | Months to years |
| Secondary malignancy | Cyclophosphamide-related (bladder carcinoma, haematological malignancies); long-term immunosuppression increases general cancer risk | Years to decades |
| Infertility | Cyclophosphamide gonadal toxicity — risk is dose-dependent (higher cumulative dose = higher risk); more severe in older patients | Permanent |
| Osteoporosis / fractures | Prolonged corticosteroid use → bone loss | Months to years |
| Psychological morbidity | Young patients facing lifelong dialysis; steroid-related mood disturbance; chronic illness burden | Throughout |
| Category | Complication | Mechanism |
|---|---|---|
| Disease — Renal | ESRD (66% at 5 years) | Crescentic destruction of glomeruli |
| Disease — Renal | Hyperkalaemia, acidosis, fluid overload, uraemia | AKI metabolic consequences |
| Disease — Pulmonary | DAH, respiratory failure | Antibody-mediated pulmonary capillaritis |
| Disease — Haematological | Iron-deficiency anaemia | Iron sequestration from chronic DAH |
| Disease — Thrombotic | DVT/PE, renal vein thrombosis | Proteinuria-related hypercoagulability + immobilisation |
| Disease — Infection | Bacterial infections | Urinary Ig loss + uraemic immunosuppression |
| Treatment — Steroids | Infection, DM, osteoporosis, AVN, peptic ulcer, psychosis | Multiple mechanisms as above |
| Treatment — Cyclophosphamide | Leucopaenia, haemorrhagic cystitis, infertility, secondary malignancy | Alkylating agent toxicity |
| Treatment — Rituximab | Infusion reactions, HBV reactivation, PML, hypogammaglobulinaemia | B cell depletion effects |
| Treatment — Plasma exchange | Hypotension, hypocalcaemia, coagulopathy, line sepsis | Extracorporeal circuit effects |
| Long-term | CKD progression, CVD, pulmonary fibrosis, malignancy, infertility | Cumulative disease and treatment burden |
High Yield Summary — Complications of Anti-GBM Disease
-
ESRD is the principal complication — 66% of patients at 5 years despite treatment. The most important prognostic factor is the degree of renal impairment at diagnosis.
-
DAH is the most immediately life-threatening complication — can cause fatal respiratory failure; present in 40–60% of patients.
-
AKI metabolic emergencies (hyperkalaemia, acidosis, fluid overload, uraemia) are common and may require emergency dialysis. Remember the mnemonic: AEIOU for dialysis indications.
-
Treatment toxicity is significant: cyclophosphamide causes leucopaenia, haemorrhagic cystitis, infertility, and secondary malignancy; steroids cause infection, diabetes, osteoporosis; plasma exchange causes hypocalcaemia and coagulopathy.
-
Relapse is rare ( < 2%) — the disease is self-limiting, unlike ANCA vasculitis.
-
Post-transplant recurrence must be prevented by waiting until anti-GBM Ab negative ≥ 6 months. Alport syndrome patients risk de novo anti-GBM disease in the graft (5–10%).
-
Always balance treatment benefit vs toxicity: patients with fibrous crescents and dialysis-dependent at presentation gain little from aggressive immunosuppression — spare them the toxicity.
Active Recall — Complications of Anti-GBM Disease
References
[1] Senior notes: Adrian Lui Pediatrics Notes.pdf (p. 326 — RPGN and crescent formation) [2] Senior notes: Ryan Ho Urogenital.pdf (p. 68 — Anti-GBM management, prognosis, and post-transplant recurrence) [4] Senior notes: Ryan Ho Fundamentals.pdf (p. 361 — RPGN presentation and fibrous crescents) [15] Senior notes: Ryan Ho Critical Care.pdf (p. 25–26 — AKI complications and dialysis indications) [16] Senior notes: Maksim Medicine Notes.pdf (p. 230–232 — Management of nephrotic syndrome complications including thrombosis)
High Yield Summary
Anti-GBM Disease — Key Points:
-
Definition: Autoimmune disease with IgG antibodies against the NC1 domain of α3 chain of type IV collagen (Goodpasture antigen) in the GBM (and alveolar BM)
-
Goodpasture's syndrome = anti-GBM disease + pulmonary haemorrhage (40–60% of cases)
-
Epidemiology: Rare (1.64/million/year), bimodal (young males = lung + kidney; older patients = kidney only), 15–20% of RPGN
-
Key risk factor for lung involvement: SMOKING (exposes the normally sequestered alveolar basement membrane antigen)
-
HLA association: HLA-DRB1*1501/1502
-
Pathognomonic finding: Linear IgG staining on immunofluorescence (Type I RPGN)
-
EM: GBM disruption without immune deposits (distinguishes from immune complex GN)
-
Clinical presentation: RPGN (haematuria, RBC casts, rapidly rising creatinine, oliguria) ± pulmonary haemorrhage (SOB, haemoptysis, CXR infiltrates, ↑DLCO)
-
Proteinuria is sub-nephrotic because ↓↓GFR limits total protein excretion
-
↑DLCO is counterintuitive but occurs because haemoglobin in alveoli binds CO
-
ANCA co-positivity in 10–50% — indicates better treatment response
-
Post-transplant anti-GBM can occur in Alport syndrome patients receiving a normal kidney
-
Without treatment: > 90% → dialysis or death
-
RPGN classification (IF-based): Type I (linear) = anti-GBM; Type II (granular) = immune complex; Type III (negative) = pauci-immune/ANCA
High Yield Summary — Differential Diagnosis of Anti-GBM Disease
-
Always send anti-GBM, ANCA, ANA/anti-dsDNA, complement, and ASOT simultaneously — do not wait for results sequentially; RPGN is a time-critical emergency
-
Complement levels split the differential: ↓C3/C4 = immune complex (lupus, PSGN, MPGN, cryoglobulinaemia, IE); Normal C3/C4 = anti-GBM, ANCA vasculitis, IgAN, HSP
-
IF pattern on renal biopsy is the definitive differentiator: Linear = anti-GBM; Granular = immune complex; Negative = pauci-immune/ANCA
-
The two most important differentials for pulmonary-renal syndrome: ANCA vasculitis (GPA/MPA) and anti-GBM disease. ANCA vasculitis has systemic features (rash, sinusitis, neuropathy); anti-GBM is organ-specific (kidney ± lung only)
-
10–50% of anti-GBM patients are ANCA co-positive — always send both; double-positive disease has slightly better treatment response
-
PSGN self-resolves; anti-GBM does not — the critical distinction in a child/young adult with acute nephritis
-
IgAN complement is NORMAL despite being immune complex-mediated (IgA does not efficiently activate classical complement) — don't be fooled
High Yield Summary — Diagnosis of Anti-GBM Disease
-
Diagnosis requires: Positive anti-GBM antibody (ELISA) AND/OR linear IgG on renal biopsy IF, in the context of RPGN ± DAH
-
"The kidney biopsy is the 'gold standard' for diagnostic evaluation of glomerular diseases" (KDIGO 2021 — GC lecture slide) [5]
-
Send anti-GBM, ANCA, ANA, anti-dsDNA, complement, ASOT all simultaneously — this is a time-critical emergency
-
Complement is NORMAL in anti-GBM disease — low complement points to immune complex GN
-
"Immunofluorescence pattern most helpful for diagnosis" [4][6] — Linear IgG = anti-GBM; Granular = immune complex; Negative = pauci-immune
-
EM shows GBM disruption WITHOUT immune deposits — distinguishes from IC-mediated GN
-
DLCO is paradoxically elevated in alveolar haemorrhage — highly specific finding
-
Biopsy prognosticates: Cellular crescents = treatable; fibrous crescents = irreversible
-
Never delay treatment for biopsy if serology is positive and clinical picture fits — "Can give empirical pulse IV methylprednisolone before renal Bx if indicated" [1][4]
-
~5% are seronegative — if clinical suspicion high, proceed to biopsy even with negative ELISA
High Yield Summary — Management of Anti-GBM Disease
-
Triple therapy: Plasma exchange + corticosteroids + cyclophosphamide (or rituximab) — targets three pathological processes: remove antibodies, suppress inflammation, prevent new antibody synthesis
-
"IV pulse MP × 3 days + oral prednisolone ± cyclophosphamide / IV rituximab ± plasma exchange" [3]
-
Plasma exchange is ESSENTIAL in anti-GBM disease (not optional like in most ANCA vasculitis) — physically removes pathogenic IgG
-
Start treatment IMMEDIATELY — "Can give empirical pulse IV methylprednisolone before renal Bx if indicated" [1][4]
-
Treatment indication: Pulmonary haemorrhage (always treat) or non-dialysis-dependent renal disease. Dialysis-dependent patients with fibrous crescents unlikely to benefit
-
"Most important prognostic factor is degree of renal impairment at diagnosis" [2]
-
Disease is self-limiting — antibody production is transient; relapse rate < 2% [2]; no long-term maintenance needed
-
"Monitor anti-GBM titres Q1–2w until negative on two occasions" [2]
-
5-year survival: Patient 83%, renal 34% [2]
-
Transplantation: Wait until anti-GBM negative ≥ 6 months; Alport patients risk de novo anti-GBM disease post-transplant
High Yield Summary — Complications of Anti-GBM Disease
-
ESRD is the principal complication — 66% of patients at 5 years despite treatment. The most important prognostic factor is the degree of renal impairment at diagnosis.
-
DAH is the most immediately life-threatening complication — can cause fatal respiratory failure; present in 40–60% of patients.
-
AKI metabolic emergencies (hyperkalaemia, acidosis, fluid overload, uraemia) are common and may require emergency dialysis. Remember the mnemonic: AEIOU for dialysis indications.
-
Treatment toxicity is significant: cyclophosphamide causes leucopaenia, haemorrhagic cystitis, infertility, and secondary malignancy; steroids cause infection, diabetes, osteoporosis; plasma exchange causes hypocalcaemia and coagulopathy.
-
Relapse is rare ( < 2%) — the disease is self-limiting, unlike ANCA vasculitis.
-
Post-transplant recurrence must be prevented by waiting until anti-GBM Ab negative ≥ 6 months. Alport syndrome patients risk de novo anti-GBM disease in the graft (5–10%).
-
Always balance treatment benefit vs toxicity: patients with fibrous crescents and dialysis-dependent at presentation gain little from aggressive immunosuppression — spare them the toxicity.
Systemic Sclerosis
Systemic sclerosis is a chronic autoimmune connective tissue disease characterized by widespread vascular dysfunction, fibrosis of the skin and internal organs, and immune dysregulation.
Eosinophilic Granulomatosis with Polyangiitis (Churg-Strauss Syndrome)
Eosinophilic granulomatosis with polyangiitis is an ANCA-associated small- and medium-vessel vasculitis characterized by asthma, peripheral eosinophilia, and extravascular eosinophilic granulomas affecting multiple organ systems.