Membranoproliferative glomerulonephritis is a pattern of glomerular injury characterized by mesangial cell proliferation, mesangial matrix expansion, and thickening of the glomerular basement membrane due to subendothelial immune complex deposits or complement dysregulation, resulting in a lobular appearance on light microscopy and a "tram-track" double-contour pattern on silver stain.

Membranoproliferative Glomerulonephritis (MPGN)

2. Epidemiology

3. Anatomy and Function Review

To understand MPGN you must understand glomerular microanatomy:

4. Etiology

A. Immune Complex-Mediated MPGN (IF: Ig + Complement)

These are driven by chronic antigenemia → persistent immune complex formation → deposition in the glomerulus → complement activation via the classical pathway → inflammation and MPGN pattern.

Infection	Mechanism	HK Relevance
Hepatitis C virus (HCV)	Chronic HCV → mixed cryoglobulinaemia (type II) → cryoglobulins deposit in glomeruli → complement activation. HCV extrahepatic manifestation: MPGN (screening recommended) ^[4]	Genotypes 1 and 6 commonest in HK ^[4]
Hepatitis B virus (HBV)	HBsAg-HBsAb immune complexes deposit in glomeruli	HBV/HCV-related MPGN is listed as a secondary proliferative GN ^[1]^[2]
Infective endocarditis	Chronic bacteraemia → immune complex formation	Universal
Shunt nephritis	Infected ventriculoatrial shunts → chronic antigenemia	Rare but classic
Other chronic infections	Malaria, schistosomiasis, mycobacterial	Less relevant in HK

Disease	Mechanism
Systemic lupus erythematosus (SLE)	Anti-dsDNA and other antibodies → immune complex deposition. Lupus nephritis can produce MPGN pattern (especially Class III/IV) ^[2]^[5]
Cryoglobulinaemia	Types I, II, III — proteins precipitate at cold temperatures, deposit in glomeruli
Sjögren syndrome	Immune complex-mediated

Condition	Mechanism
Monoclonal gammopathy of renal significance (MGRS)	Monoclonal Ig (from a small B-cell clone) deposits in glomeruli. The clone is too small to qualify as myeloma/lymphoma but big enough to cause kidney damage
Multiple myeloma	Monoclonal light/heavy chains deposit. An old man with bone pain and anaemia — myeloma must be excluded in older patients with MPGN ^[6]
Waldenström macroglobulinaemia	IgM paraprotein deposition
Chronic lymphocytic leukaemia (CLL)	Paraprotein-mediated

High Yield — HKUMed Exam Point: In an older patient (> 40 years) presenting with MPGN pattern on biopsy, you must screen for monoclonal gammopathy (serum and urine protein electrophoresis, serum free light chains, immunofixation). This is MGRS until proven otherwise ^[6].

IF shows dominant C3 deposition with absent or minimal immunoglobulin staining. This defines the entity of C3 glomerulopathy (C3G), which is subdivided by EM into:

Subtype	EM Appearance	Pathogenesis
C3 Glomerulonephritis (C3GN)	Mesangial, subendothelial, and/or subepithelial electron-dense deposits (varied locations)	Dysregulation of the alternative complement pathway
Dense Deposit Disease (DDD) (formerly MPGN Type II)	Characteristic highly electron-dense, ribbon-like intramembranous deposits within the GBM (the deposits are so electron-dense they look like a dark stripe running through the GBM)	Uncontrolled alternative pathway activation — often due to C3 nephritic factor (C3NeF), an autoantibody that stabilizes C3 convertase, preventing its normal breakdown

Why does complement dysregulation cause MPGN?

Uncontrolled C3 activation → C3b deposition on GBM and mesangium → recruitment of inflammatory cells → mesangial proliferation → GBM damage → characteristic MPGN pattern
Causes of alternative pathway dysregulation:
- C3 nephritic factor (C3NeF): autoantibody against C3bBb convertase → stabilizes it → persistent C3 cleavage → low serum C3
- Genetic mutations: Factor H, Factor I, Factor B, C3, MCP/CD46 — loss-of-function in regulatory proteins or gain-of-function in activation proteins
- Anti-Factor H antibodies: acquired inhibition of complement regulation

Complement Connection

Think of it this way: if the "brakes" on the alternative complement pathway are broken (loss of Factor H, Factor I) or the "accelerator" is stuck (C3NeF stabilizing the convertase), complement activation runs unchecked → C3 fragments deposit on the GBM → inflammation → MPGN pattern. This is analogous to how atypical HUS is also a disease of complement dysregulation, but affecting the endothelium of small vessels rather than the glomerular mesangium.

5. Pathophysiology — Linking Etiology to Histology to Clinical Features

Feature	Mechanism
Heavy proteinuria / nephrotic syndrome	GBM structural disruption + podocyte injury → loss of size/charge selectivity
Haematuria	Inflammatory disruption of GBM integrity → RBC leakage
Hypertension	Reduced GFR → sodium/water retention; also RAAS activation
Renal impairment	Reduced capillary lumen from mesangial proliferation; crescent formation if severe
Low complement	Consumption via classical (immune complex) or alternative (C3G) pathway

MPGN characteristically shows: proteinuria (++), nephrotic (++), nephritic (+), haematuria (+), ARF (+), CRF (+) — it is the quintessential "mixed" glomerulonephritis ^[3].

Persistently low C3 > 8 weeks raises the possibility of lupus nephritis or membranoproliferative glomerulonephritis (complement-mediated MPGN) ^[7].

Etiology	C3	C4	Pathway Activated
Post-streptococcal GN	↓ (transient, normalizes by 8 weeks)	Normal	Alternative
MPGN (immune complex-mediated, e.g. HCV/cryoglobulinaemia)	↓	↓	Classical
MPGN (C3 glomerulopathy / DDD)	↓↓ (often profoundly low)	Normal	Alternative
Lupus nephritis	↓	↓	Classical

Clinical Pearl — Persistently Low C3

A common exam trap: PSGN causes low C3 that normalizes within 6–8 weeks. If C3 remains low beyond 8 weeks, you must consider MPGN or lupus nephritis. Do NOT label it as "persistent PSGN" — re-investigate! ^[7]

6. Classification

Type	Deposit Location (EM)	Modern Equivalent
MPGN Type I	Subendothelial + mesangial deposits	Immune complex-mediated MPGN or C3GN
MPGN Type II	Intramembranous dense deposits	Dense Deposit Disease (C3G)
MPGN Type III	Subendothelial + subepithelial deposits	Immune complex-mediated MPGN or C3GN

Category	IF Pattern	Subtypes	Key Causes
Immune complex-mediated MPGN	Ig + C3	—	HCV, HBV, SLE, cryoglobulinaemia, MGRS
Complement-mediated (C3 Glomerulopathy)	C3 dominant, Ig-negative/trace	C3GN, DDD	C3NeF, Factor H/I mutations, anti-Factor H Ab

7. Clinical Features

Symptom	Pathophysiological Basis
Haematuria (gross or microscopic — "tea-coloured" or "cola-coloured" urine)	Inflammatory breach of the GBM → RBCs leak into Bowman's space → dysmorphic RBCs in urine. May be gross (especially during intercurrent infections which boost immune complex formation)
Frothy urine	Heavy proteinuria → protein in urine creates foam (proteins reduce surface tension of urine)
Peripheral oedema (face, periorbital in mornings; leg swelling later in day)	Two mechanisms: (1) nephrotic: hypoalbuminaemia → decreased oncotic pressure → fluid shifts to interstitium; (2) nephritic: sodium/water retention from reduced GFR
Weight gain	Fluid retention (oedema)
Oliguria / reduced urine output	Reduced GFR from mesangial proliferation occluding capillary lumens + inflammatory swelling
Fatigue / malaise	Uraemia from declining renal function; anaemia from chronic disease
Headache	Hypertension secondary to sodium/water retention
Nausea / poor appetite	Uraemia (accumulation of nitrogenous waste)
Dyspnoea	Fluid overload → pulmonary oedema (if severe nephrotic/nephritic syndrome)

Symptoms related to underlying cause:

Underlying Cause	Associated Symptoms
HCV	Fatigue, arthralgia, Raynaud phenomenon, purpura (cryoglobulinaemia), skin manifestations (porphyria cutanea tarda, lichen planus) ^[4]
HBV	May be asymptomatic carrier; jaundice if active hepatitis
SLE	Facial rash (malar/butterfly rash), photosensitivity, oral ulcers, hair loss, arthralgia of small joints, Raynaud phenomenon, serositis (pleurisy, pericarditis) ^[5]
Cryoglobulinaemia	Purpura, arthralgia, peripheral neuropathy, Raynaud phenomenon
Monoclonal gammopathy / Myeloma	Bone pain, anaemia, hypercalcaemia, weight loss, recurrent infections ^[6]
Infective endocarditis	Fever, new murmur, splinter haemorrhages, Janeway lesions, Osler nodes

Sign	Pathophysiological Basis
Hypertension	Reduced GFR → activation of RAAS (renin-angiotensin-aldosterone system) → sodium/water retention → volume expansion → elevated BP. Hypertension is a hallmark of nephritic syndrome
Peripheral oedema (pitting)	Nephrotic: ↓albumin → ↓intravascular oncotic pressure → fluid extravasation. Nephritic: ↓GFR → Na+/H₂O retention → volume expansion
Periorbital oedema (especially morning)	Loose periorbital connective tissue allows fluid accumulation early; gravity-dependent oedema (legs) develops later in the day
Ascites / pleural effusion (if severe nephrotic syndrome)	Profound hypoalbuminaemia → third-space fluid collection
Pallor	Anaemia of chronic kidney disease (reduced erythropoietin) or haemolytic anaemia if associated with TMA
Xanthelasma / tendon xanthomata (rare, chronic nephrotic syndrome)	Hyperlipidaemia secondary to nephrotic syndrome (liver upregulates lipoprotein synthesis in response to hypoalbuminaemia)
Lipodystrophy (partial)	Specifically associated with C3 glomerulopathy / DDD — loss of subcutaneous fat (especially upper body) due to complement-mediated adipocyte lysis (C3NeF activates complement in adipose tissue)
Signs of underlying disease	Malar rash (SLE), purpura (cryoglobulinaemia/vasculitis), hepatomegaly/stigmata of chronic liver disease (HBV/HCV), splenomegaly (lymphoproliferative disease)

Finding	Significance
Dysmorphic RBCs	Glomerular origin haematuria — RBCs are deformed as they squeeze through the damaged GBM
RBC casts	Pathognomonic of glomerulonephritis — RBCs trapped in Tamm-Horsfall protein matrix in the tubules
Proteinuria (subnephrotic to nephrotic range)	GBM damage → loss of size/charge selectivity
Lipiduria (oval fat bodies, fatty casts)	In nephrotic-range proteinuria; filtered lipoproteins and free cholesterol in urine

MPGN — The Great Mimicker

MPGN can present as virtually any glomerular syndrome: asymptomatic proteinuria/haematuria, acute nephritic syndrome, nephrotic syndrome, mixed nephritic-nephrotic, RPGN (if crescents develop), or slowly progressive CKD. The clinical presentation depends on the severity of histological changes and the underlying cause. Always look for the underlying driver — especially HCV, HBV, SLE, cryoglobulinaemia, and monoclonal gammopathy.

From the nephrology data interpretation table ^[3]:

Feature	MPGN Rating
Proteinuria	++
Nephrotic	++
Nephritic	+
Haematuria	+
ARF	+
CRF	+

This highlights that MPGN is a "jack of all trades" — moderate across all clinical presentations. Compare this to MCD (pure nephrotic, no haematuria) or PSGN (pure nephritic, minimal proteinuria).

9. Histopathological Features (Essential for Understanding)

Since renal biopsy is still essential for definitive diagnosis of MPGN ^[8], understanding the histology is key:

From lecture slides ^[1]^[2]:

Term	Definition
Focal	< 50% of glomeruli involved
Diffuse	> 50% of glomeruli involved
Segmental	< 50% of area within a single glomerulus involved
Global	> 50% of area within a single glomerulus involved
Proliferative	Increased cellularity from proliferation of native glomerular cells or WBC infiltration
Membrane thickening	Thickening of GBM per se, or more often due to protein (esp Ab or immune complex) deposition either side of or within the GBM
Crescent formation	Cellular crescents from proliferating epithelial cells + infiltrating leukocytes — pathognomonic of RPGN
Sclerosis	Replacement of glomerular tissue by hyaline fibrous scar tissue

High Yield Summary

Definition: MPGN is a histological pattern (not a single disease) defined by mesangial proliferation + GBM thickening/duplication ("tram-track") on light microscopy.

Modern Classification (pathogenesis-based):

Immune complex-mediated MPGN (IF: Ig + C3) — caused by HCV, HBV, SLE, cryoglobulinaemia, MGRS/myeloma, infective endocarditis
Complement-mediated / C3 Glomerulopathy (IF: C3 dominant, Ig-negative) — subdivided into C3GN and DDD; caused by alternative complement pathway dysregulation (C3NeF, Factor H/I mutations)

Clinical Presentation: Mixed nephrotic-nephritic picture. Proteinuria (++), haematuria (+), nephrotic (++), nephritic (+), ARF (+), CRF (+). Can present as any glomerular syndrome.

Key Diagnostic Clue: Persistently low C3 > 8 weeks (unlike PSGN which normalizes by 8 weeks) — think MPGN or lupus nephritis.

Complement Pattern:

IC-MPGN (classical pathway): ↓C3, ↓C4
C3G (alternative pathway): ↓↓C3, normal C4

Must-Exclude Causes in HK: HCV (with cryoglobulins), HBV, SLE, monoclonal gammopathy (especially in older patients).

Histology Hallmarks: Tram-track GBM (LM), lobular accentuation (LM), IF pattern determines subtype, DDD has intramembranous dense deposits (EM).

Renal biopsy is essential for definitive diagnosis and to guide treatment.

Active Recall - Membranoproliferative Glomerulonephritis

Differential Diagnosis of MPGN

The Major Differentials — Explained From First Principles

Why it's in the DDx: PSGN is the prototypical acute nephritic syndrome — haematuria, oedema, hypertension, oliguria, with low C3. The acute presentation of MPGN may be indistinguishable from PSGN, but MPGN usually persists beyond 4–6 weeks with further increase in serum creatinine ^[11].

Feature	PSGN	MPGN
Latent period	1–3 weeks after pharyngitis, 3–6 weeks after skin infection ^[11]	No characteristic latent period
Age	Most common in children aged 5–12 ^[12]	Any age; bimodal (children for C3G, adults for IC-MPGN)
C3	Low, normalizes by 4–8 weeks ^[7]^[11]	Persistently low
C4	Normal (alternative pathway)	Low if classical pathway (IC-MPGN), normal if alternative (C3G)
Clinical course	Self-limiting; diuresis in 1–2 weeks, RFT normalizes in 4 weeks ^[11]	Progressive; does NOT spontaneously resolve
ASO titre	May be raised ^[7]	Not elevated
Renal biopsy	Usually NOT done ^[11]	Required for definitive diagnosis
EM	Subepithelial humps ("starry sky") ^[13]	Subendothelial deposits (Type I) or intramembranous dense deposits (DDD)

The discriminating principle: Time. PSGN resolves. MPGN does not. If clinical features or low C3 persist beyond 6–8 weeks, suspect MPGN.

Why it's in the DDx: Lupus nephritis is classified as a secondary proliferative GN ^[2] and can produce an MPGN-like histological pattern (especially Class III/IV diffuse proliferative lupus nephritis). It also causes hypocomplementaemia. In Hong Kong, SLE is relatively common in young Chinese women.

Feature	Lupus Nephritis	MPGN
Demographics	Young women (F:M ~9:1), especially East Asian	No strong sex predilection
Extrarenal features	Malar rash, photosensitivity, oral ulcers, arthralgia, serositis, hair loss ^[5]	Usually no extrarenal features (unless secondary to SLE or HCV)
Complement	↓C3 and ↓C4 (classical pathway) ^[10]	↓C3 ± ↓C4 depending on mechanism
Autoantibodies	ANA positive, anti-dsDNA positive ^[9]	ANA/anti-dsDNA negative (unless MPGN is secondary to SLE)
IF pattern	"Full house" — IgG, IgA, IgM, C3, C1q	Granular Ig + C3 (IC-MPGN) or C3-dominant (C3G)

The discriminating principle: Systemic features of SLE + positive ANA/anti-dsDNA + "full house" IF. If your MPGN patient has positive ANA and extrarenal features — think lupus nephritis as the underlying driver.

Lupus or MPGN?

Remember: SLE can cause an MPGN histological pattern. So the real question is — is this primary MPGN, or is this lupus nephritis presenting with an MPGN pattern? Check ANA, anti-dsDNA, and look for extrarenal SLE features.

Why it's in the DDx: IgA nephropathy is the most common primary GN globally and in Hong Kong ^[14]. It can present with haematuria and proteinuria, occasionally with nephrotic features. However, the clinical pattern differs.

Feature	IgA Nephropathy	MPGN
Classic presentation	Recurrent synpharyngitic haematuria — gross haematuria within 1–2 days of URTI ^[15]. "Syn-" means simultaneous, not delayed like PSGN.	No temporal relationship to infections
Complement	Normal C3 and C4 — IgA nephropathy is NOT usually associated with complement consumption ^[11]	Low C3 ± low C4
IF pattern	Dominant mesangial IgA deposits	IgG/IgM/C3 (IC-MPGN) or C3-dominant (C3G)
Serum IgA	Elevated in ~50% ^[15]	Not elevated
Histology	Mesangial proliferative GN (MEST criteria)	Mesangial + endocapillary proliferative + GBM duplication

The discriminating principle: Normal complement + synpharyngitic timing + mesangial IgA on biopsy = IgA nephropathy, not MPGN.

Why it's in the DDx: Essential mixed cryoglobulinaemia (Type II) is a classic cause of immune complex-mediated MPGN. It is strongly associated with HCV ^[4]. The clinical presentation overlaps heavily with MPGN because cryoglobulinaemia IS one of the causes of MPGN.

Feature	Cryoglobulinaemia	Primary MPGN
Triad	Purpura + arthralgia + weakness (Meltzer triad)	No classic triad
Complement	↓C3, ↓↓C4 (classical pathway activation with disproportionately low C4)	Variable
Serum cryoglobulins	Positive cryocrit ^[9]	Negative
Associated infection	HCV (> 90% of mixed cryoglobulinaemia cases) ^[4]	May or may not have HCV
Peripheral neuropathy	Common (vasa nervorum involvement)	Not typical

The discriminating principle: Disproportionately low C4, palpable purpura, positive cryocrit, and HCV seropositivity all point to cryoglobulinaemia.

Why it's in the DDx: ANCA vasculitis (GPA, MPA, EGPA) can cause rapidly progressive GN with haematuria and proteinuria, mimicking MPGN. However, it is a fundamentally different mechanism — pauci-immune (no or minimal immune deposits on IF) ^[16].

Feature	ANCA Vasculitis	MPGN
ANCA	Positive (c-ANCA/PR3 for GPA; p-ANCA/MPO for MPA) ^[9]	Negative
Complement	Normal	Low
IF	Negative (pauci-immune) — this is the hallmark ^[16]	Positive (Ig ± C3)
Extrarenal features	Sinusitis, epistaxis, pulmonary nodules (GPA); purpura, neuropathy (MPA)	Usually none unless secondary cause
Histology	Crescentic GN (necrotizing)	Mesangial proliferative + GBM duplication

The discriminating principle: Normal complement + positive ANCA + pauci-immune IF = vasculitis, not MPGN.

Why it's in the DDx: Presents with RPGN (haematuria, rapidly declining renal function) ± pulmonary haemorrhage. Can be confused with severe MPGN presenting as RPGN.

Feature	Anti-GBM Disease	MPGN
Pulmonary haemorrhage	Classic (Goodpasture syndrome) — haemoptysis, dyspnoea, infiltrates on CXR ^[16]	Not typical
Anti-GBM Ab	Positive ^[9]	Negative
Complement	Normal	Low
IF	Linear IgG staining along GBM ^[16]	Granular (IC-MPGN) or C3-dominant (C3G)
Speed of decline	Days to weeks (RPGN)	Usually more indolent (weeks to months)
Treatment	Plasmapheresis (to remove circulating anti-GBM antibodies) ^[16]	Depends on etiology

The discriminating principle: Linear IF staining + positive anti-GBM antibody + pulmonary-renal syndrome.

Why it's in the DDx: Both MPGN and membranous nephropathy cause nephrotic syndrome with GBM thickening. However, membranous nephropathy is non-proliferative ^[2] and presents with a bland sediment.

Feature	Membranous Nephropathy	MPGN
Sediment	Bland (inactive) sediment — oval fat bodies, hyaline casts, few RBCs ^[10]	Active sediment — dysmorphic RBCs, RBC casts ^[15]
Complement	Normal	Low
Proliferation	No proliferation (non-proliferative GN) ^[2]	Proliferative
Anti-PLA2R	Positive in ~70% of primary cases ^[15]	Negative
EM	Subepithelial deposits ("spike and dome") ^[15]	Subendothelial (Type I) or intramembranous (DDD)

The discriminating principle: Bland sediment + normal complement + non-proliferative histology = membranous. Active sediment + low complement + proliferative histology = MPGN.

Why they're in the DDx: Both cause nephrotic syndrome, which MPGN can also cause. However:

Feature	MCD / FSGS	MPGN
Sediment	Bland ^[10]	Active
Complement	Normal	Low
Haematuria	Absent (MCD) or minimal (FSGS) ^[3]	Present
Hypertension	Less common acutely	Common
EM	Podocyte effacement (MCD); segmental sclerosis (FSGS)	GBM duplication, mesangial interposition

Once the renal biopsy shows an MPGN pattern, the IF results divide you into two camps:

The IF pattern is the key discriminator for determining the underlying cause of MPGN:

IF Finding	Category	Differential of Underlying Cause
Ig + C3 (granular)	Immune complex-mediated	HBV/HCV, SLE (Class IV), Cryoglobulinaemia, MGRS/Myeloma/CLL, Malignancy (lung/breast/ovary), Infective endocarditis ^[13]^[19]
C3-dominant (Ig-negative)	C3 Glomerulopathy	C3GN or DDD — due to alternative complement pathway dysregulation (C3NeF, Factor H/I mutations, anti-Factor H Ab)

This is a critical distinction because:

Immune complex-mediated MPGN → treat the underlying cause (e.g., DAAs for HCV, immunosuppression for SLE, chemotherapy for MGRS)
C3 Glomerulopathy → complement-directed therapies are being explored; prognosis is generally worse

High Yield: Type I MPGN: HBV/HCV, Autoimmune diseases (SLE Class IV, Cryoglobulinaemia), Malignancy (CLL/MM/Lung/Breast/Ovary). Type II and III MPGN: Idiopathic ^[13]^[19].

Diagnosis	Complement	ANCA	Anti-GBM	ANA/dsDNA	Cryoglobulins	IF Pattern	Key Clinical Clue
MPGN (IC-mediated)	↓C3 ± ↓C4	−	−	−	±	Granular Ig + C3	Mixed nephrotic/nephritic, persistent
MPGN (C3G/DDD)	↓↓C3, N C4	−	−	−	−	C3-dominant	Young patient, ± lipodystrophy
PSGN	↓C3 (transient)	−	−	−	−	Granular IgG/C3	Post-strep, self-resolving ≤ 4–8 wk
Lupus nephritis	↓C3, ↓C4	−	−	+	±	"Full house"	Young woman, systemic features
Cryoglobulinaemia	↓C3, ↓↓C4	−	−	−	+	Granular	Purpura, neuropathy, HCV+
IgA nephropathy	Normal	−	−	−	−	Mesangial IgA	Synpharyngitic haematuria
ANCA vasculitis	Normal	+	−	−	−	Pauci-immune	ENT/pulmonary/skin vasculitis
Anti-GBM disease	Normal	±	+	−	−	Linear IgG	Pulmonary-renal syndrome
Membranous	Normal	−	−	−	−	Granular IgG/C3 (subepithelial)	Bland sediment, anti-PLA2R+
MCD	Normal	−	−	−	−	Negative	Pure nephrotic, children

Age-stratified differential of glomerulonephritis ^[15]:

Age Group	Nephrotic Presentation	Nephritic Presentation
< 15 years	MCD, FSGS	PSGN, IgA nephropathy / HSP
15–40 years	MCD, FSGS, Membranous	IgA nephropathy, PSGN, Lupus nephritis, RPGN
> 40 years	MCD, Membranous, DM, Amyloidosis	PSGN, IgA nephropathy, RPGN

MPGN can appear at any age but is not the commonest cause in any age group — it is always a "must-consider" differential rather than the leading diagnosis. C3 glomerulopathy/DDD tends to present in children/young adults, whereas immune complex-mediated MPGN (especially HCV-associated or MGRS) is more common in adults.

High Yield Summary — Differential Diagnosis of MPGN

The clinical presentation of MPGN (mixed nephrotic-nephritic with low complement) must be differentiated from: PSGN, lupus nephritis, IgA nephropathy, cryoglobulinaemia, ANCA vasculitis, anti-GBM disease, membranous nephropathy, and MCD/FSGS.
Complement levels are the most powerful bedside discriminator:
- ↓C3 only → PSGN (transient), C3G, infective endocarditis GN
- ↓C3 + ↓C4 → Lupus, IC-MPGN, cryoglobulinaemia
- Normal complement → IgA nephropathy, ANCA vasculitis, anti-GBM, MCD, FSGS, membranous
Persistent low C3 > 8 weeks → think MPGN or lupus nephritis, NOT PSGN
Once MPGN pattern is confirmed on biopsy, IF determines the category:
- Ig + C3 → Immune complex-mediated → search for HCV, HBV, SLE, cryoglobulinaemia, MGRS
- C3-dominant → C3 Glomerulopathy → complement studies (C3NeF, Factor H, genetic testing)
In elderly patients with MPGN: always screen for monoclonal gammopathy (SIEP, UIEP, serum free light chains)
Renal biopsy (LM/IF/EM) is essential for definitive diagnosis and to guide treatment

Active Recall - DDx of MPGN

References

^[2] Senior notes: Ryan Ho Urogenital.pdf (p54 — Classification of GN by cellularity) ^[3] Senior notes: Block A – Nephrology Data Interpretation.pdf (p17 — Clinical presentation table of GN) ^[4] Senior notes: Ryan Ho GI.pdf (p232 — HCV extrahepatic manifestations including MPGN) ^[5] Lecture slides: GC 046. Facial rash and painful fingers_SLE.pdf ^[6] Lecture slides: GC 030. An old man with bone pain and anaemia.pdf ^[7] Senior notes: Block A - Glomerular and Tubulo-interstitial Diseases and Acute Kidney Injury.pdf (p19 — Persistently low C3) ^[9] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p1008 — Biochemical tests for GN diagnosis) ^[10] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p433 — Nephrotic syndrome diagnosis, C3/C4 levels) ^[11] Senior notes: Adrian Lui Pediatrics Notes.pdf (p328 — PSGN clinical features and DDx) ^[12] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p420 — PSGN epidemiology) ^[13] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p998 — MPGN description, etiology, morphology) ^[14] Senior notes: Block A - Glomerular and Tubulo-interstitial Diseases and Acute Kidney Injury.pdf (p9 — Glomerular causes of haematuria) ^[15] Senior notes: Maksim Medicine Notes.pdf (p231–233 — GN nephrotic/nephritic features, age-stratified DDx) ^[16] Senior notes: Ryan Ho Urogenital.pdf (p64 — RPGN classification by IF) ^[17] Lecture slides: Introduction-kidney-Ix.pdf (p23 — Workup for glomerulonephritis) ^[18] Lecture slides: Nephrology - ntroduction to Renal Investigation.pdf (p23 — Workup for glomerulonephritis) ^[19] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p405 — MPGN etiology by type)

Diagnostic Criteria, Algorithm & Investigations for MPGN

2. The Diagnostic Algorithm — Step by Step

Let me walk you through this the way you'd approach it on a ward round, from the moment the patient walks in to the final pathological diagnosis.

4. Investigation Modalities — Detailed Breakdown

I'll organize this as you would order them in clinical practice: bedside → bloods → urine → serology → imaging → biopsy.

Investigation	What to Look For	Interpretation in MPGN	Mechanism
Urine dipstick	Blood, protein	Blood 2–3+, protein 2–3+	GBM damage → haematuria + proteinuria
Urine microscopy	Dysmorphic RBCs, RBC casts	Present — confirms glomerular origin of haematuria ^[20]^[21]	RBCs deform as they squeeze through damaged GBM; casts form when RBCs are trapped in Tamm-Horsfall protein in tubules
Phase-contrast microscopy	Acanthocytes ( > 5%)	Highly specific for glomerular bleeding	Spiculated RBCs = passed through damaged GBM
Urine protein quantification	24-hour urine protein or spot urine protein:creatinine ratio (uPCR) or albumin:creatinine ratio (ACR)	Can be subnephrotic or nephrotic range (> 3.5 g/day). MPGN shows proteinuria ++, nephrotic ++ ^[3]	GBM structural disruption + podocyte injury → loss of size/charge barrier
Urine sediment	WBCs, WBC casts, oval fat bodies	Sterile pyuria may be present; oval fat bodies if nephrotic range proteinuria	Inflammatory cells in glomerulus spill into urine; lipiduria from filtered lipoproteins

Glomerular vs Non-Glomerular Haematuria

All haemoglobin-positive dipsticks must be accompanied by urine microscopy. Dysmorphic RBCs and RBC casts = glomerular disease. Isomorphic RBCs = urological disease (stones, tumour, infection). This distinction is fundamental and will appear in exams ^[20].

Investigation	Expected Finding in MPGN	Why You Order It
RFT (urea, creatinine, eGFR)	Variable ↓GFR — creatinine may be mildly elevated or significantly raised depending on severity ^[8]^[20]	Quantify degree of renal impairment; baseline for monitoring
CBC	Normocytic normochromic anaemia (anaemia of CKD); ± thrombocytosis (nephrotic syndrome) ^[20]	Anaemia = chronic disease/CKD; thrombocytopenia may suggest TMA or SLE
Serum albumin	Low if nephrotic syndrome ( < 30 g/L)	Hypoalbuminaemia is one of the criteria that defines nephrotic syndrome ^[10]
Lipid profile	Elevated cholesterol/TG if nephrotic	Liver upregulates lipoprotein synthesis to compensate for urinary protein loss
ESR / CRP	Usually elevated	Non-specific marker of inflammation; helps distinguish active disease from chronic scarring
Blood glucose / HbA1c	To exclude diabetic nephropathy	Diabetic nephropathy is the commonest cause of CKD and can mimic nephrotic presentation ^[22]

This is where MPGN stands out from most other GNs.

Investigation	Expected in IC-MPGN	Expected in C3G/DDD	Why
Serum C3	↓	↓↓ (often profoundly)	Hypocomplementaemia is the diagnostic hallmark of MPGN ^[13]^[19]. IC-MPGN: classical pathway consumption. C3G: alternative pathway consumption
Serum C4	↓ (classical pathway activation)	Normal (alternative pathway only)	C4 is consumed only in the classical pathway. This helps distinguish the mechanism
CH50 (total haemolytic complement)	↓	↓	Measures overall complement function — reduced in any pathway activation

GC 057 High Yield: "Total haemolytic complement activity and C3 concentrations are depressed. Persistently low C3 > 8 weeks raises the possibility of lupus nephritis or membranoproliferative glomerulonephritis." ^[23]

Advanced complement studies (for C3 Glomerulopathy workup):

Test	What It Detects	Interpretation
C3 nephritic factor (C3NeF)	Autoantibody that stabilizes C3 convertase	Positive in ~80% of DDD and ~50% of C3GN — confirms autoimmune complement dysregulation
Factor H level / anti-Factor H antibodies	Deficiency or inhibition of the main fluid-phase regulator of the alternative pathway	Low Factor H or positive anti-Factor H Ab → uncontrolled alternative pathway activation
Factor I, Factor B, MCP/CD46	Other complement regulatory proteins	Deficiency → predisposition to C3G
Genetic complement panel	Mutations in CFH, CFI, CFB, C3, CFHR genes	Identifies heritable complement dysregulation — important for prognosis and family screening
Soluble C5b-9 (membrane attack complex)	Terminal complement activation	Elevated → supports ongoing complement-mediated injury

When to Order Advanced Complement Studies

You don't order C3NeF or genetic panels on everyone. These are reserved for when the renal biopsy shows C3-dominant IF staining (i.e., C3 Glomerulopathy is confirmed). The purpose is to identify the specific complement defect, which has implications for prognosis, recurrence risk post-transplant, and potential complement-targeted therapy.

Serology for relevant conditions ^[20]^[21]:

Investigation	Purpose	Expected Result in Primary MPGN	Notes
ANA, anti-dsDNA	Lupus nephritis ^[9]^[10]	Negative	If positive → lupus nephritis causing MPGN pattern
ANCA (c-ANCA/PR3, p-ANCA/MPO)	ANCA vasculitis (GPA, MPA, EGPA) ^[9]	Negative	ANCA vasculitis is pauci-immune; different mechanism entirely
Anti-GBM antibody	Anti-GBM disease / Goodpasture ^[9]	Negative	If positive → linear IF, pulmonary-renal syndrome
HBsAg, anti-HCV, HCV RNA	HBV/HCV-related MPGN ^[9]^[17]	May be positive	HCV most often induces MPGN; HBV most often induces membranous nephropathy ^[9]. A positive serological test does NOT prove renal disease is due to HBV/HCV ^[9] — biopsy correlation needed
HIV serology	HIV nephropathy (collapsing FSGS) ^[9]	Negative	Part of standard screen
VDRL	Syphilis (associated with membranous nephropathy) ^[9]	Negative	Serological testing generally NOT performed until renal biopsy results are known ^[9]
Serum cryoglobulins (cryocrit)	Cryoglobulinaemia ^[9]^[20]	May be positive if HCV-associated	Presence of measurable cryoglobulin (cryocrit) is the most prominent laboratory hallmark of cryoglobulinaemia syndromes ^[9]. MUST keep specimen at 37°C during transport or cryoglobulins precipitate and give false negative!
ASO titre	PSGN ^[7]^[20]	Not elevated	Antibodies to streptolysin O may be raised in PSGN, but not all strains produce streptolysin O ^[7]^[23]
SIEP/UIEP + serum free light chains	Monoclonal gammopathy (MGRS/myeloma) ^[9]^[17]^[18]	May detect monoclonal band	Malignancy screen (e.g. tumour markers, SIEP) especially in elderly ^[17]^[18]. Primary amyloidosis and light chain deposition disease are associated with a monoclonal gammopathy ^[9]
Blood cultures	Infective endocarditis ^[20]	Negative (unless IE is the cause)	Order if persistent fever + murmur

The Systematic Screen — Don't Miss Anything

A very common exam and clinical error is failing to perform the full panel. Even if the clinical picture strongly suggests one diagnosis, you must exclude the others. The mnemonic for the MPGN workup panel:

"CAVE HIM"

Complement (C3, C4, CH50)
Autoantibodies (ANA, anti-dsDNA, ANCA, anti-GBM)
Viral serology (HBV, HCV, HIV)
Electrophoresis (SIEP, UIEP, serum free light chains)
History of infection (ASO, blood cultures, throat swab)
Immunoglobulins (cryoglobulins, serum Ig levels)
Malignancy screen (especially in elderly)

Investigation	Purpose	Expected Finding in MPGN	When to Order
Renal ultrasound (USG)	Assess kidney size, exclude obstruction, rule out structural causes	Normal-sized or slightly enlarged kidneys in active MPGN; small, atrophic kidneys suggest chronic irreversible disease (biopsy usually NOT helpful) ^[21]	Always — before biopsy to confirm two kidneys of adequate size and no contraindications
CXR	Pulmonary involvement, fluid overload	Pulmonary oedema if fluid-overloaded; pulmonary infiltrates/haemorrhage if Goodpasture/vasculitis	If respiratory symptoms or to assess fluid status
CT thorax / DLCO	Pulmonary involvement if cough ± haemoptysis ^[20]^[21]	Abnormal if pulmonary-renal syndrome (Goodpasture, vasculitis)	If haemoptysis or unexplained dyspnoea
Echocardiogram	Infective endocarditis if persistent fever + murmur ^[20]^[21]	Vegetations if IE is the underlying cause	If IE is clinically suspected

Renal biopsy is still essential for definitive diagnoses of membranoproliferative GN ^[8].

Why biopsy? Because:

You cannot distinguish MPGN from other GNs clinically
The IF pattern determines whether it is immune complex-mediated vs complement-mediated
The EM pattern determines the subtype (DDD vs C3GN)
Histological findings guide treatment and prognosis

Contraindications to percutaneous renal biopsy ^[24]:

Bleeding diathesis
Severe uncontrolled hypertension
Solitary kidney
Small kidneys indicative of chronic irreversible disease
Hydronephrosis
Renal or perirenal infection

How it's done: Percutaneous ultrasound-guided biopsy of the lower pole of the kidney (to avoid major vessels). Typically obtain 2 cores — one for LM/IF, one for EM.

What to look for on biopsy and the expected findings in MPGN:

Modality	Findings in MPGN	Significance
Light Microscopy (LM)	Thickening of GBM ^[13]^[19] + Hypercellularity: proliferation of endothelial and mesangial cells, infiltration of leukocytes ^[13]^[19] + Lobular accentuation of glomerular tuft + "Tram-track" / "double contour" appearance on PAS/silver stain (due to mesangial interposition) + ± Crescent formation (if severe)	Confirms the MPGN morphological pattern. The lobular, proliferative appearance with GBM duplication is the sine qua non
Immunofluorescence (IF)	IC-MPGN: Granular deposits of complement (C3, C1q) + immunoglobulins (IgG, IgM) along capillary walls and mesangium ^[13]^[19]	The IF pattern is the KEY discriminator: Ig + C3 = immune complex-mediated. C3-dominant = C3 glomerulopathy. This determines the entire downstream workup and management
	C3 Glomerulopathy: Dominant C3 staining, absent or trace Ig (C3 intensity ≥ 2 orders of magnitude > any Ig)
Electron Microscopy (EM)	IC-MPGN Type I: Subendothelial deposits ^[13]^[19]	Deposit location determines the old "type" classification. Subendothelial = Type I (commonest). Intramembranous = DDD (Type II). Subendothelial + subepithelial = Type III
	DDD (old Type II): Intramembranous dense deposits — highly electron-dense ribbon-like deposits within the lamina densa of the GBM ^[13]^[19]	Virtually pathognomonic of DDD. These are so characteristic they are recognizable at a glance
	C3GN: Variable location deposits (mesangial, subendothelial, subepithelial) — NOT the classic dense-deposit pattern	Distinguishes C3GN from DDD within the C3G category

GC 057 High Yield — Primary kidney diseases that can cause nephrotic syndrome include: focal segmental glomerulosclerosis, membranous glomerulopathy, minimal change disease, membranoproliferative glomerulonephritis, and occasionally IgA nephropathy ^[23].

Once biopsy is done, the pathologist reports back. Here is how you interpret it:

IF Finding	Diagnosis	Next Step
Ig + C3 (granular, capillary wall + mesangial)	Immune complex-mediated MPGN	Search for secondary cause: HCV (with cryoglobulins?), HBV, SLE, MGRS, IE, malignancy
C3-dominant, Ig-negative/trace	C3 Glomerulopathy	EM to subclassify → DDD vs C3GN. Then: complement studies (C3NeF, Factor H, genetic panel)
"Full house" (IgG, IgA, IgM, C3, C1q)	Lupus nephritis (MPGN pattern)	Confirm with clinical criteria + ANA/anti-dsDNA. Classify ISN/RPS class
Ig + C3 with organized deposits (fibrillar/microtubular)	Cryoglobulinaemic GN or immunotactoid GN	Check cryocrit, HCV status. EM: organized deposits (fibrils ~20 nm for cryo, ~30–50 nm for immunotactoid)
Monotypic Ig (single light chain class)	MGRS-associated MPGN	Haematology referral. Confirm with SIEP/UIEP/serum free light chains. Bone marrow biopsy

Category	Tests	Rationale
Urinalysis	Dipstick, microscopy, uPCR/24h protein	Confirm glomerular haematuria and quantify proteinuria
Basic bloods	RFT, CBC, albumin, lipids, glucose	Assess renal function, nephrotic features, exclude DM
Complement	C3, C4, CH50	The single most important serological discriminator for MPGN
Autoimmune	ANA, anti-dsDNA, ANCA, anti-GBM	Exclude lupus, vasculitis, anti-GBM disease
Infection screen	HBV, HCV, HIV, VDRL, ASO, blood cultures	Exclude infection-driven immune complex MPGN
Paraprotein screen	SIEP, UIEP, serum free light chains	Exclude MGRS/myeloma (especially in elderly)
Cryoglobulins	Cryocrit	Exclude cryoglobulinaemia (often HCV-associated)
Imaging	Renal USG, CXR, ± echo	Kidney size (biopsy feasibility), fluid status, exclude IE
Renal biopsy	LM, IF, EM	Definitive diagnosis. IF pattern classifies the mechanism
Complement studies (if C3G)	C3NeF, Factor H/I/B, genetic panel	Identify specific complement defect for targeted therapy

High Yield Summary — Diagnosis of MPGN

MPGN is a histopathological diagnosis — there are no standalone clinical diagnostic criteria. Definitive diagnosis requires renal biopsy with LM/IF/EM.
Clinical clues raising suspicion: Mixed nephrotic-nephritic picture + persistently low C3 (> 8 weeks) + active urine sediment.
Pre-biopsy workup (mnemonic "CAVE HIM"): Complement, Autoantibodies, Viral serology, Electrophoresis/paraprotein, History of infection, Immunoglobulins/cryoglobulins, Malignancy screen.
IF is the KEY discriminator on biopsy:
- Ig + C3 → Immune complex-mediated → hunt for HCV, HBV, SLE, cryoglobulinaemia, MGRS
- C3-dominant → C3 Glomerulopathy → complement studies (C3NeF, Factor H, genetics)
EM subclassifies C3G: DDD (intramembranous dense deposits) vs C3GN (variable location deposits).
Do NOT forget paraprotein screen in elderly patients — MGRS is treatable and commonly missed.
Complement pattern:
- ↓C3, ↓C4 = classical pathway = IC-MPGN, lupus, cryoglobulinaemia
- ↓↓C3, normal C4 = alternative pathway = C3 Glomerulopathy
- Transient ↓C3 (normalizes ≤ 8 wk) = PSGN

Active Recall - Diagnosis of MPGN

References

^[3] Senior notes: Block A – Nephrology Data Interpretation.pdf (p17 — Clinical presentation table of GN) ^[7] Senior notes: Block A - Glomerular and Tubulo-interstitial Diseases and Acute Kidney Injury.pdf (p19 — Persistently low C3, PSGN investigations) ^[8] Senior notes: Block A - Nephrotology Teaching Clinic RTD.pdf (p3–4 — Diagnosis of renal diseases, renal biopsy essential for MPGN) ^[9] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p1008 — Biochemical tests for GN diagnosis) ^[10] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p433 — Nephrotic syndrome diagnosis, C3/C4 levels) ^[11] Senior notes: Adrian Lui Pediatrics Notes.pdf (p328 — PSGN clinical features and DDx) ^[13] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p998 — MPGN description, etiology, morphology) ^[17] Lecture slides: Introduction-kidney-Ix.pdf (p23 — Workup for glomerulonephritis) ^[18] Lecture slides: Nephrology - ntroduction to Renal Investigation.pdf (p23 — Workup for glomerulonephritis) ^[19] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p405 — MPGN etiology and morphology by type) ^[20] Senior notes: Ryan Ho Urogenital.pdf (p63 — Evaluation of nephritic syndrome, serology workup) ^[21] Senior notes: Adrian Lui Pediatrics Notes.pdf (p325 — Evaluation of nephritic syndrome) ^[22] Senior notes: Block A - Chronic Kidney Disease and its Complications.pdf (p8 — Causes of CKD) ^[23] Lecture slides: GC 057. Glomerular and Tubulo-interstitial Diseases and Acute Kidney Injury.pdf (p8, p9, p36, p41) ^[24] Senior notes: MBBS Final MB (Surgery) (Felix PY Lai).pdf (p770 — Renal biopsy contraindications)

Management of MPGN

1. Supportive Care — For ALL Patients With MPGN

Regardless of the underlying cause, every patient with MPGN receives supportive care. These measures are common to all glomerulonephropathies and are frequently tested in SAQs.

General management of nephrotic/nephritic syndrome (SAQ!) ^[15]:

Parameter	Method	Rationale
I/O (intake/output)	Fluid balance chart	Detect fluid overload or hypovolaemia from over-diuresis
Vitals	BP, HR, temp, SpO2	Hypertension monitoring is critical — drives progressive renal damage
Body weight daily	Aim ~1 kg/day loss if oedematous ^[15]	Weight gain = fluid retention. Too rapid diuresis → hypovolaemia → pre-renal AKI
Urine dipstick	Daily in acute phase	Track proteinuria and haematuria trends
RFT	Serial (daily if AKI, otherwise weekly–fortnightly)	Detect deteriorating renal function early

Monitoring of blood pressure and body weight, home urine dipstick monitoring ^[25].

Intervention	Details	Mechanism	Cautions
Low sodium diet	Na+ restriction to max 2 g/day ^[25]	Reduces tubular sodium reabsorption → less water retention → less oedema	Must be balanced with nutritional needs
Fluid restriction	~50% maintenance if severe oedema ^[25]	Reduces intravascular volume addition	Generally not needed unless severe
Diuretics	High-dose frusemide ± thiazide ± spironolactone ^[15]	Frusemide (loop diuretic) blocks NKCC2 in thick ascending limb → natriuresis. Adding thiazide (blocks NCC in DCT) provides sequential nephron blockade for synergistic effect. Spironolactone (blocks aldosterone receptor in collecting duct) → K+-sparing + additional natriuresis	Furosemide ± spironolactone ONLY indicated in severe symptomatic oedema with normal intravascular status ^[25]. May precipitate hypovolaemic shock, AKI, and increased thrombosis risk in patients with marked hypoalbuminaemia and intravascular volume depletion

Why is diuretic use tricky in nephrotic syndrome? In nephrotic patients, the low albumin means oncotic pressure is already reduced, so intravascular volume may be DECREASED even though total body water is INCREASED (oedema). Aggressive diuresis can cause intravascular depletion → pre-renal AKI. Think of it as: the water is in the wrong compartment.

Albumin infusion: Reserved as adjunct to diuretics only for diuretic-resistant oedema with oliguria/uraemia in the absence of severe glomerular damage ^[26]. IV albumin transiently raises oncotic pressure, pulling fluid back into the intravascular space, but is quickly lost in the urine due to the leaky GBM — so the benefit is short-lived.

Anti-proteinuric drugs (ACEI/ARB): for ALL glomerulopathies — ↓glomerular pressure, ↓rate of GFR decline ^[15].

Drug Class	Examples	Mechanism	Target	Contraindications
ACEI	Ramipril, perindopril, lisinopril	Inhibits ACE → ↓angiotensin II → preferential efferent arteriolar dilation → ↓intraglomerular pressure → ↓filtration pressure across the GBM → ↓proteinuria	Proteinuria < 1 g/day or uPCR < 0.5–1 g/g ^[26]	Bilateral renal artery stenosis (removes the efferent arteriolar tone that maintains GFR in the setting of poor renal perfusion → precipitous GFR drop) ^[27]; hyperkalaemia; pregnancy
ARB	Losartan, valsartan, irbesartan	Blocks AT1 receptor → same downstream effect as ACEI on efferent arteriole	Same as ACEI	Same as ACEI

Why do they work? Angiotensin II normally constricts the efferent arteriole more than the afferent. This maintains intraglomerular pressure (useful in dehydration). In glomerular disease, this high pressure is harmful — it pushes more protein across the damaged GBM. By blocking angiotensin II, you dilate the efferent arteriole → drop intraglomerular pressure → less "force" pushing protein through → less proteinuria → slower progression.

ACEI or ARB is a compelling indication in both diabetes and chronic kidney disease ^[28].

Never Combine ACEI + ARB

Never prescribe ACEI and ARB together — this has been shown to cause more harm (hyperkalaemia, AKI) without benefit in multiple trials (ONTARGET, VA NEPHRON-D) ^[27].

Statins: if hyperlipidaemia persists after treatment ^[15].

Drug	Indication	Mechanism
Statins (atorvastatin, rosuvastatin)	Persistent hyperlipidaemia despite treatment of underlying nephrotic syndrome	HMG-CoA reductase inhibition → ↓hepatic cholesterol synthesis → ↓LDL. In nephrotic syndrome, the liver upregulates lipoprotein production to compensate for urinary albumin loss. Statins counteract this and reduce long-term cardiovascular risk

DVT prophylaxis: compressive stockings ± anticoagulation if high risk ^[15].

Why are nephrotic patients hypercoagulable? Because:

Urinary loss of antithrombin III (a natural anticoagulant — small enough to be filtered through damaged GBM)
Compensatory hepatic upregulation of procoagulant factors (fibrinogen, factors V, VII, VIII)
Thrombocytosis (reactive)
Hyperviscosity from haemoconcentration

Intervention	Indication	Notes
Compression stockings	All immobilized nephrotic patients	Low-risk, non-pharmacological
Therapeutic anticoagulation	Usually only if thromboembolic events occur ^[26]	Not routinely prophylactic
Prophylactic anticoagulation	High-risk patients: very low albumin ( < 20 g/L), membranous nephropathy, prolonged immobility ^[26]	Risk-benefit must be weighed against bleeding risk

2. Cause-Specific Treatment — The Critical Layer

This is one of the most common identifiable causes of immune complex-mediated MPGN, especially in adults. The treatment has been revolutionized by direct-acting antivirals (DAAs).

Treatment	Details	Mechanism	When to Use
Direct-acting antivirals (DAAs)	Sofosbuvir-based regimens (e.g., sofosbuvir/velpatasvir for 12 weeks)	Directly inhibit HCV replication → ↓viral load → ↓immune complex formation → ↓glomerular deposition → disease remission	First-line for ALL HCV-associated MPGN. Achieves sustained virological response (SVR) in > 95%. SVR leads to renal improvement in most patients
Rituximab	Anti-CD20 monoclonal antibody	Depletes B cells → ↓cryoglobulin-producing B-cell clones → ↓immune complex formation	Added to DAAs if severe cryoglobulinaemic vasculitis (progressive renal failure, skin vasculitis, neuropathy)
Plasmapheresis	Removes circulating cryoglobulins and immune complexes	Rapid reduction of pathogenic circulating proteins	Life-threatening cryoglobulinaemic flare (e.g., rapidly progressive GN, pulmonary haemorrhage) — bridge while waiting for DAA/rituximab to take effect
Avoid interferon-based regimens	Old standard; no longer first-line	Interferon can exacerbate cryoglobulinaemia and autoimmunity	Superseded by DAAs

DAA Revolution

Before 2014, HCV-associated MPGN was treated with interferon + ribavirin (poor cure rates, significant toxicity). DAAs have transformed outcomes: > 95% SVR, well-tolerated, shorter courses. If SVR is achieved and cryoglobulinaemia resolves, the MPGN often remits completely.

Treatment	Details	Notes
Antiviral therapy	Entecavir or tenofovir alafenamide (TAF)	Suppresses HBV replication → ↓HBsAg-HBsAb immune complex formation. Tenofovir disoproxil fumarate (TDF) has renal tubular toxicity risk; TAF is preferred for renal safety ^[29]
Avoid immunosuppression alone	Steroids/cyclophosphamide without antivirals can cause HBV reactivation and hepatic flare	Always start antivirals BEFORE or concurrently with any immunosuppression

SLE management depends on severity ^[30]:

Severity	Regimen
Induction (Class III/IV LN — the types producing MPGN pattern)	HCQ (for ALL SLE patients) + IV pulse methylprednisolone 0.5–1 g/day × 3 days followed by oral prednisolone taper + MMF (mycophenolate mofetil) or IV cyclophosphamide ^[30]
Maintenance	HCQ + low-dose steroids + MMF (preferred) or azathioprine ^[30]
Refractory	Rituximab (anti-CD20) or belimumab (anti-BAFF) ^[30]

Why MMF? Mycophenolate (myco = fungal origin, phenolate = phenolic acid derivative) inhibits inosine monophosphate dehydrogenase → blocks de novo purine synthesis → selectively suppresses lymphocyte proliferation (lymphocytes depend on de novo pathway more than other cells which can use salvage pathway). This makes it relatively lymphocyte-selective with fewer side effects than cyclophosphamide.

Why cyclophosphamide? An alkylating agent that cross-links DNA → prevents cell replication. Potent but toxic: risk of haemorrhagic cystitis (prevent with mesna + hydration), infection (PCP prophylaxis with co-trimoxazole), gonadal toxicity (fertility preservation discussion essential), and malignancy. Reserved for severe or refractory disease.

Treatment	Details	Rationale
Clone-directed therapy	Haematology referral. Regimens depend on the clone type: bortezomib-based (if plasma cell), rituximab-based (if B-cell), or other chemotherapy	The principle is to eliminate the B-cell/plasma cell clone producing the pathogenic monoclonal immunoglobulin. If you eliminate the source, the immune complex deposition stops and the kidney can recover
Avoid "watch and wait"	Unlike MGUS (which is benign), MGRS causes organ damage — even though the clone is small	MGRS is defined by the presence of renal damage attributable to the monoclonal protein. It needs treatment even if haematological criteria for myeloma/lymphoma are not met

Treatment	Details
Prolonged IV antibiotics	Treat the endocarditis per guidelines (typically 4–6 weeks of bactericidal IV antibiotics). Once infection is eradicated, the antigenemia resolves → immune complex deposition stops → GN improves
Surgery	If valve destruction, heart failure, or persistent bacteraemia

When the full workup is negative for secondary causes:

Idiopathic MPGN: steroid ± cyclophosphamide (if deteriorating renal function) ^[15].

Treatment	Indication	Regimen	Evidence
Supportive care only	Mild disease: stable renal function, subnephrotic proteinuria	ACEI/ARB + BP control + monitoring	Reasonable approach given limited evidence for immunosuppression in idiopathic IC-MPGN
Corticosteroids	Nephrotic syndrome and/or progressive renal impairment	Oral prednisolone (starting dose ~1 mg/kg/day, taper over months)	Limited evidence; some observational studies suggest benefit
Cyclophosphamide	Deteriorating renal function despite steroids ^[15]	Added to steroid regimen (oral or IV pulse)	Used as second-line escalation; significant toxicity (haemorrhagic cystitis, infection, gonadotoxicity)
MMF	Alternative to cyclophosphamide (less toxic)	Used increasingly in practice as a steroid-sparing agent	Small case series; no RCTs

Evidence Gap — Honest Assessment

The evidence base for immunosuppressive treatment of idiopathic MPGN is weak. There are no large randomized controlled trials. Most data comes from small observational studies and case series. KDIGO 2021 guidelines recommend a cautious approach: supportive care first, immunosuppression only if progressive disease. This contrasts with well-established protocols for lupus nephritis or ANCA vasculitis.

C3G is the trickiest to manage because it is driven by complement dysregulation, and conventional immunosuppression (designed to suppress immune cells) does not directly address the complement pathway defect.

Treatment	Indication	Mechanism	Evidence Level
Supportive care + ACEI/ARB	All patients	Standard anti-proteinuric + renoprotective	Universally recommended
MMF	Progressive disease with active inflammation on biopsy	Suppresses lymphocyte proliferation; may reduce production of C3NeF (an autoantibody)	Observational; some patients respond
Corticosteroids	Active inflammatory disease	Anti-inflammatory	Variable response; some benefit reported
Eculizumab	Refractory progressive C3G, especially if terminal complement activation is prominent	Monoclonal antibody against C5 → blocks formation of membrane attack complex (C5b-9). "Eculizumab" = anti-C5 ("ecul-" from Latin equi- = "equal/block", targeting C5)	Case reports and small series; mixed results. Best evidence in patients with elevated soluble C5b-9. Not universally effective
Iptacopan / danicopan	Emerging complement-targeted therapies — Factor B inhibitors	Block Factor B → inhibit alternative pathway C3 convertase formation → reduce C3 activation	Phase 2/3 trials ongoing as of 2025–2026. Promising preliminary data
Anti-C3 therapy (pegcetacoplan)	Investigational for C3G	Monoclonal antibody/peptide targeting C3 directly	Early-phase trials
Plasmapheresis	C3G with C3NeF (autoantibody) — theoretically can remove the autoantibody	Removes circulating C3NeF	Limited evidence; used in acute flares

Key point about C3G management: The field is rapidly evolving. Complement-targeted therapies represent a paradigm shift because they address the root cause (complement dysregulation) rather than non-specifically suppressing the immune system. However, as of 2026, evidence remains limited to small studies.

4. Management of Specific Complications

A critically important point: MPGN has a high recurrence rate in the transplanted kidney, especially C3 Glomerulopathy.

Type	Recurrence Risk Post-Transplant	Notes
IC-MPGN (secondary)	Low if underlying cause is treated (e.g., SVR for HCV, remission of SLE)	Address the cause before/during transplant
IC-MPGN (idiopathic)	Moderate (~30–50%)	May recur but usually less aggressive
C3 Glomerulopathy (C3GN)	~50–70%	High recurrence risk because the complement defect is systemic, not confined to the native kidney
Dense Deposit Disease (DDD)	> 80%	Very high recurrence; DDD has the worst post-transplant prognosis of all GNs. The complement dysregulation continues to damage the graft

Implications: Genetic complement testing before transplantation is essential for C3G patients. If a specific complement mutation is identified, targeted complement blockade (e.g., eculizumab prophylaxis) may be considered peri-transplant, though evidence is still evolving.

MPGN Subtype	First-Line Treatment	Second-Line / Refractory	Key Principle
HCV ± cryoglobulinaemia	DAAs (sofosbuvir-based) ± rituximab	Plasmapheresis for severe cryo flare	Cure the virus → cure the MPGN
HBV	Entecavir or tenofovir (TAF)	—	Always antiviral before/with immunosuppression
Lupus nephritis	HCQ + steroids + MMF or cyclophosphamide	Rituximab, belimumab	Follow SLE nephritis protocols (ISN/RPS class)
MGRS	Clone-directed therapy (haem referral)	—	Eliminate the monoclonal clone
Infective endocarditis	Prolonged IV antibiotics ± surgery	—	Eradicate infection → GN resolves
Idiopathic IC-MPGN	Supportive + ACEI/ARB. Steroids if progressive	+ Cyclophosphamide if deteriorating RFT ^[15]	Limited evidence; treat conservatively first
C3GN	Supportive + ACEI/ARB. MMF or steroids if progressive	Eculizumab (refractory); emerging Factor B inhibitors	Complement-targeted therapy is the future
DDD	Supportive + ACEI/ARB	Eculizumab (very variable response); complement studies to guide	Worst prognosis; highest transplant recurrence

High Yield Summary — Management of MPGN

The overarching principle: TREAT THE UNDERLYING CAUSE. MPGN management is not one-size-fits-all.
Supportive care for ALL patients:
- ACEI/ARB (anti-proteinuric, renoprotective — for ALL glomerulopathies)
- Low sodium diet + diuretics (frusemide ± thiazide ± spironolactone) for oedema
- Statins if persistent hyperlipidaemia
- DVT prophylaxis
- Monitoring: I/O, BP, body weight (aim ~1 kg/day loss), urine dipstick, serial RFT
Cause-specific treatment:
- HCV → DAAs ± rituximab ± plasmapheresis
- HBV → Entecavir/TAF (always before immunosuppression)
- SLE → HCQ + steroids + MMF/cyclophosphamide
- MGRS → Clone-directed therapy
- IE → Prolonged antibiotics
- Idiopathic → Steroids ± cyclophosphamide if deteriorating RFT
C3 Glomerulopathy: Supportive + immunosuppression (MMF/steroids) for progressive disease; eculizumab for refractory cases; emerging complement-targeted therapies (Factor B inhibitors).
Prognosis: poor — 50% ESRD at 10 years. High transplant recurrence especially for DDD ( > 80%) and C3GN (~50–70%).
Never combine ACEI + ARB. Never immunosuppress HBV patients without antivirals. Never give NSAIDs to patients with renal impairment.

Active Recall - Management of MPGN

References

^[8] Senior notes: Block A - Nephrotology Teaching Clinic RTD.pdf (p3–4 — Diagnosis of renal diseases, renal biopsy for MPGN) ^[13] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p998 — MPGN description, prognosis) ^[15] Senior notes: Maksim Medicine Notes.pdf (p231–233 — MPGN management, general nephrotic/nephritic management) ^[16] Senior notes: Ryan Ho Urogenital.pdf (p64 — RPGN management, empirical pulse methylprednisolone) ^[17] Lecture slides: Introduction-kidney-Ix.pdf (p23 — Workup for glomerulonephritis) ^[18] Lecture slides: Nephrology - ntroduction to Renal Investigation.pdf (p23 — Workup for glomerulonephritis) ^[19] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p405 — MPGN etiology, prognosis) ^[22] Senior notes: Block A - Chronic Kidney Disease and its Complications.pdf (p8, p17 — Causes of CKD, therapeutic objectives) ^[25] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p435 — General management of nephrotic syndrome) ^[26] Senior notes: Ryan Ho Fundamentals.pdf (p368 — General approach to nephrotic syndrome management) ^[27] Senior notes: Block A – Nephrology Data Interpretation.pdf (p11 — ACEI/ARB precautions, bilateral RAS) ^[28] Senior notes: Block A - High blood pressure_ hypertension.pdf (p42 — Compelling indications for ACEI/ARB) ^[29] Senior notes: Block A - Drugs and the Kidney.pdf (p9 — TDF renal toxicity, direct tubular toxicity) ^[30] Senior notes: Ryan Ho Rheumatology.pdf (p76 — SLE management by severity) ^[31] Senior notes: Ryan Ho Critical Care.pdf (p25–26 — AKI management, dialysis indications) ^[32] Senior notes: Block A - Glomerular and Tubulo-interstitial Diseases and Acute Kidney Injury.pdf (p28 — Chronic GN treatment principles)

Complications of MPGN

MPGN carries a poor prognosis in general — 50% develop end-stage disease in 10 years after diagnosis ^[13]^[19]. Understanding the complications is therefore critical, both for exam purposes and for counselling patients. The complications arise from two sources: (1) the glomerular disease itself (loss of filtration barrier integrity, progressive nephron loss, chronic inflammation) and (2) consequences of nephrotic syndrome (hypoalbuminaemia, hypercoagulability, immunodeficiency).

Let me walk through each complication from first principles so you understand why it happens rather than just memorizing a list.

This is the most important and most feared long-term complication.

Why does MPGN progress to CKD?

The ongoing glomerular inflammation (mesangial proliferation, GBM damage, complement activation) leads to a vicious cycle:

Active glomerulitis → loss of functioning nephrons
Remaining nephrons undergo compensatory hyperfiltration (each surviving nephron handles a larger share of the total filtration workload)
Hyperfiltration damages the remaining glomeruli (increased intraglomerular pressure → further GBM injury → proteinuria → tubulointerstitial fibrosis)
Progressive sclerosis (hyaline scar tissue replaces functional glomeruli) → further nephron loss
End result: shrunken, fibrotic kidneys = end-stage renal disease

Chronic glomerulonephritis is an important cause of CKD ^[32]^[33]. Chronic GN presents as progressive kidney function loss in patients with glomerular inflammation, proteinuria, haematuria, and often hypertension. If untreated or poorly controlled, it leads to CKD ^[32].

Laboratory evaluation of chronic GN: CBC shows normochromic normocytic anaemia; RFT shows progressive ↑serum urea, creatinine, ↑PO4, ↓Ca ± ↑K+ and metabolic acidosis; USG shows variable degrees of kidney shrinkage ^[32]^[33].

CKD Stage	eGFR	Clinical Implication
Stage 1	≥ 90	Kidney damage with normal or ↑GFR — often asymptomatic
Stage 2	60–89	Mild ↓GFR — few symptoms
Stage 3	30–59	Moderate ↓GFR — metabolic complications begin
Stage 4	15–29	Severe ↓GFR — prepare for RRT
Stage 5	< 15	Kidney failure — RRT required

MPGN prognosis: 50% develop ESRD within 10 years ^[13]^[19].

Preparation for renal replacement therapy if approaching stage 5 CKD (eGFR < 15) ^[32].

CKD Complications — High Yield for Exams

Six systemic complications of CKD ^[22]:

Fluid retention
Metabolic acidosis
High blood pressure
Normochromic normocytic anaemia
Secondary hyperparathyroidism
Bone disease (CKD-MBD)

Each of these can develop as MPGN progresses to advanced CKD.

Metabolic Consequences of CKD (Explained)

Complication	Mechanism	Clinical Feature
Hyperkalaemia	Kidneys cannot excrete K+ → accumulates. Worsened by acidosis (H+/K+ exchange), ACEI/ARB use	ECG changes (peaked T waves, widened QRS), arrhythmias, muscle weakness
Metabolic acidosis (HAGMA)	Kidneys cannot excrete H+ or regenerate HCO₃⁻. Also cannot excrete organic acids → high anion gap	Kussmaul breathing (deep, laboured — compensatory hyperventilation), fatigue, nausea
Hyperphosphataemia + hypocalcaemia	Kidneys cannot excrete PO₄³⁻ → elevated serum phosphate → binds calcium → ↓free calcium. Also ↓1α-hydroxylation of vitamin D (this happens in the kidney) → ↓active vitamin D → ↓gut calcium absorption	Bone pain, fractures, tetany (severe hypocalcaemia), vascular calcification
Secondary hyperparathyroidism	The low calcium and high phosphate both stimulate PTH release from the parathyroid glands → chronically elevated PTH	Bone resorption (renal osteodystrophy), brown tumours, subperiosteal erosions
Normochromic normocytic anaemia	Damaged kidneys produce insufficient erythropoietin (EPO) → ↓red cell production. Also: uraemic toxins suppress erythropoiesis and shorten RBC lifespan	Pallor, fatigue, dyspnoea on exertion

MPGN with nephrotic-range proteinuria creates a hypercoagulable state. This is one of the most dangerous acute complications.

Why are nephrotic patients hypercoagulable? (from first principles)

Factor	Mechanism
Loss of antithrombin III (AT III)	AT III (molecular weight ~58 kDa) is small enough to be filtered through the damaged GBM and lost in the urine. AT III is the body's major natural anticoagulant — it inactivates thrombin and factors Xa, IXa, XIa. Its loss tips the balance towards clotting
Increased procoagulant factor synthesis	The liver senses hypoalbuminaemia → ramps up protein synthesis non-selectively → overproduces fibrinogen, factors V, VII, VIII, and von Willebrand factor
Thrombocytosis	Reactive thrombocytosis from hepatic thrombopoietin overproduction (as part of the general hepatic synthetic upregulation)
Hyperviscosity	Haemoconcentration from intravascular volume depletion (fluid shifts to interstitium due to low oncotic pressure)
Impaired fibrinolysis	Loss of plasminogen in urine; elevated plasminogen activator inhibitor-1 (PAI-1)

Specific Thromboembolic Complications

Complication	Clinical Features	Investigation	Management
Renal vein thrombosis	Flank pain, sudden worsening of proteinuria, haematuria, acute kidney injury (thrombosis obstructs renal venous outflow)	Doppler USG, CT angiography ^[15]	If AKI: thrombolysis ± embolectomy. If non-AKI: LMWH/UFH → warfarin for minimum 6–12 months while still nephrotic ^[15]
Deep vein thrombosis (DVT)	Unilateral leg swelling, warmth, tenderness	Doppler USG of legs; D-dimer	Anticoagulation (LMWH → warfarin/DOAC)
Pulmonary embolism (PE)	Sudden dyspnoea, pleuritic chest pain, tachycardia, hypoxia	CTPA, V/Q scan	Anticoagulation; thrombolysis if massive/haemodynamically unstable
Cerebral venous sinus thrombosis	Headache, focal neurological deficits, seizures	CT/MRI venography	Anticoagulation

DVT prophylaxis: compressive stockings ± anticoagulation if high risk ^[15].

Why are MPGN patients at increased risk of infection?

Urinary loss of immunoglobulins (IgG): Immunoglobulins, especially IgG (~150 kDa), can be filtered through the severely damaged GBM. Loss of IgG → impaired opsonization → susceptibility to encapsulated organisms (Streptococcus pneumoniae, Haemophilus influenzae, Neisseria meningitidis)
Urinary loss of complement factors: Further impairs innate immunity (complement is already being consumed by the disease process in MPGN)
Immunosuppressive therapy: Steroids, cyclophosphamide, MMF, rituximab all suppress the immune system → increased risk of opportunistic and conventional infections
Protein malnutrition: From heavy urinary protein loss → impaired immune cell function

Infection	Mechanism	Special Notes
Spontaneous bacterial peritonitis (SBP) — mainly in children with nephrotic syndrome ^[15]	Loss of IgG + ascitic fluid (if present) becomes a bacterial culture medium. S. pneumoniae is the most common organism	SBP is classically associated with nephrotic syndrome in children, not adults. Treat with antibiotics
Pneumonia (especially pneumococcal)	Loss of IgG + complement	Pneumococcal vaccination is indicated for ALL nephrotic patients
Cellulitis	Oedematous skin provides a portal of entry; impaired immune defences	Common in grossly oedematous patients
PCP (Pneumocystis jirovecii pneumonia)	Immunosuppression from cyclophosphamide or high-dose steroids	PCP prophylaxis with co-trimoxazole must be given when using cyclophosphamide or rituximab
CMV, BK virus	Particularly post-transplant (immunosuppression for graft + prevention of recurrence)	Monitor viral loads post-transplant

Resistant oedema management ^[15]:

Cause	Mechanism	Management
Poor drug/diet compliance	Patient not adhering to sodium restriction or diuretic regimen	Education, dietitian referral
Frusemide malabsorption due to gut wall oedema	In severe nephrotic syndrome, oedema of the bowel wall reduces oral frusemide absorption — the drug never reaches systemic circulation	Change to IV frusemide ^[15]
Diuretic resistance	Compensatory distal tubular sodium reabsorption overwhelms loop diuretic effect	Add thiazide (sequential nephron blockade) ± potassium-sparing diuretics. IV albumin as adjunct ^[15]

Patients with MPGN are vulnerable to superimposed AKI from several mechanisms:

AKI in nephrotic syndrome ^[15]:

Cause	Mechanism	Management
Hypovolaemia due to over-diuresis	Aggressive diuretic use removes intravascular volume (already depleted by low oncotic pressure) → pre-renal AKI	Lower dose / withhold diuretics; rehydration ^[15]
Acute tubular necrosis (ATN)	Prolonged pre-renal state from hypovolaemia → ischaemic tubular injury. Also nephrotoxic drugs (NSAIDs, aminoglycosides, contrast)	Stop offending agents, supportive care
Crescentic transformation (RPGN)	Severe glomerular injury → crescent formation → rapid GFR decline	Urgent immunosuppression (pulse steroids ± cyclophosphamide)
Bilateral renal vein thrombosis	Obstruction of venous outflow from both kidneys → acute renal congestion → ↓GFR	Thrombolysis ± embolectomy

The immunosuppressive therapies used to treat MPGN carry their own complication profile:

Drug	Complications	Prevention
Corticosteroids (long-term)	Cushing syndrome, osteoporosis, diabetes, hypertension, cataracts, avascular necrosis of femoral head, growth retardation in children, mood disturbance, peptic ulcer, opportunistic infections	Lowest effective dose; bone protection (calcium + vitamin D ± bisphosphonate); PPI if indicated; glucose monitoring
Cyclophosphamide	Haemorrhagic cystitis (acrolein metabolite damages bladder epithelium), gonadotoxicity (infertility), bone marrow suppression, increased malignancy risk (especially bladder cancer, haematological malignancy), infection	Mesna to prevent haemorrhagic cystitis; PCP prophylaxis; fertility preservation discussion; regular CBC monitoring
MMF (mycophenolate)	GI disturbance (diarrhoea, nausea), bone marrow suppression, teratogenicity	Regular CBC; effective contraception
Rituximab	Infusion reactions, progressive multifocal leukoencephalopathy (PML — rare but devastating), hepatitis B reactivation, hypogammaglobulinaemia	Pre-medicate for infusion; check HBV status before use; monitor immunoglobulin levels
Eculizumab (complement blockade)	Meningococcal infection — blocking C5 prevents formation of the membrane attack complex (C5b-9) which is essential for killing Neisseria meningitidis	Meningococcal vaccination (ACWY + B) is MANDATORY before starting eculizumab — patients must be vaccinated at least 2 weeks before first dose; prophylactic antibiotics (penicillin) may also be given
Calcineurin inhibitors (cyclosporine, tacrolimus)	Nephrotoxicity (ironic — treating kidney disease with a nephrotoxin), hypertension, tremor, gingival hyperplasia (cyclosporine), diabetes (tacrolimus)	Therapeutic drug monitoring; careful dose adjustment

This was discussed in the management section but deserves emphasis as a complication:

Long-term complications following kidney transplant include recurrence of primary disease ^[34].

MPGN Subtype	Recurrence Rate	Impact
IC-MPGN (secondary — cause treated)	Low (~10–20%) if cause is controlled	Good graft survival if HCV cured with DAAs, SLE in remission, etc.
IC-MPGN (idiopathic)	~30–50%	Variable graft impact
C3 Glomerulonephritis	~50–70%	Significant cause of graft loss
Dense Deposit Disease	> 80%	Worst recurrence of any GN; major contributor to graft failure

Why is recurrence so high in C3G/DDD? Because the complement dysregulation is systemic — it's a problem with circulating complement proteins or autoantibodies (C3NeF, anti-Factor H), not a problem intrinsic to the native kidney. The new kidney is immediately exposed to the same dysfunctional complement environment. Unless complement blockade is achieved (e.g., eculizumab), the same pathological process attacks the graft.

Remember that MPGN is driven by an underlying disease, and that underlying disease has its own complications:

Underlying Cause	Additional Complications Beyond MPGN
HCV	Cirrhosis, hepatocellular carcinoma, other extrahepatic manifestations (lymphoma, neuropathy, porphyria cutanea tarda)
HBV	Cirrhosis, HCC, HBV reactivation with immunosuppression
SLE	Multi-organ involvement (CNS, skin, joints, serositis, haematological), antiphospholipid syndrome, accelerated atherosclerosis
MGRS/Myeloma	Bone disease, hypercalcaemia, anaemia, recurrent infections, amyloidosis, hyperviscosity (Waldenström)
Infective endocarditis	Valvular destruction, heart failure, septic emboli (stroke, splenic/renal infarcts), mycotic aneurysms

Complication	Mechanism (Brief)	Time Frame	Key Management
CKD → ESRD	Progressive nephron loss, sclerosis	Years	Supportive care, ACEI/ARB, preparation for RRT
RPGN (crescentic)	Severe GBM breach → crescent formation	Days–weeks	Urgent immunosuppression ± plasmapheresis
Thromboembolism (RVT, DVT, PE)	Loss of AT III, ↑clotting factors, thrombocytosis	Acute	Anticoagulation; thromboprophylaxis
Infection	Loss of Ig, complement; immunosuppression	Any time	Vaccination, PCP prophylaxis, infection surveillance
Cardiovascular disease	Hyperlipidaemia, hypertension, uraemia, chronic inflammation	Long-term	Statins, BP control, CV risk modification
Resistant oedema	Severe hypoalbuminaemia, gut wall oedema reducing frusemide absorption	Acute/subacute	IV frusemide, add thiazide, IV albumin
AKI (superimposed)	Over-diuresis, ATN, crescentic transformation, RVT	Acute	Fluid management, stop nephrotoxins, immunosuppression if crescentic
Treatment complications	Drug-specific toxicities	Any time	Monitoring, prophylaxis (mesna, PCP Ppx, meningococcal vaccine)
Disease recurrence post-transplant	Systemic complement/immune complex disease persists	Post-transplant	Complement blockade, cause-directed therapy, close graft monitoring

High Yield Summary — Complications of MPGN

CKD → ESRD is the most important long-term complication: 50% reach ESRD within 10 years. CKD complications include fluid retention, metabolic acidosis, hypertension, anaemia, secondary hyperparathyroidism, and bone disease.
Crescentic transformation (RPGN) can cause loss of renal function in days to weeks. Cellular crescents may respond to immunosuppression; fibrous crescents are irreversible. Early treatment is critical.
Thromboembolic complications (renal vein thrombosis, DVT, PE) arise from loss of AT III in urine + hepatic overproduction of clotting factors. DVT prophylaxis for all high-risk nephrotic patients.
Infection from loss of immunoglobulins + immunosuppressive therapy. Pneumococcal vaccination for ALL nephrotic patients. PCP prophylaxis with cyclophosphamide/rituximab. Meningococcal vaccination before eculizumab.
Cardiovascular disease from hyperlipidaemia, hypertension, and chronic inflammation. Long-term risk modification essential.
Post-transplant recurrence is very high, especially for DDD ( > 80%) and C3GN (~50–70%). The complement defect is systemic, not kidney-intrinsic.

Active Recall - Complications of MPGN

References

^[3] Senior notes: Block A – Nephrology Data Interpretation.pdf (p17 — Clinical presentation table of GN) ^[13] Senior notes: MBBS Final MB (Medicine) (Felix PY Lai).pdf (p998 — MPGN prognosis) ^[15] Senior notes: Maksim Medicine Notes.pdf (p231–232 — General management, complications of nephrotic syndrome) ^[16] Senior notes: Ryan Ho Fundamentals.pdf (p361 — RPGN, crescent formation, management) ^[19] Senior notes: MBBS Final MB (Pediatrics) (Felix PY Lai).pdf (p405 — MPGN prognosis) ^[22] Senior notes: Block A - Chronic Kidney Disease and its Complications.pdf (p23 — Six complications of CKD) ^[32] Senior notes: Block A - Glomerular and Tubulo-interstitial Diseases and Acute Kidney Injury.pdf (p28 — Chronic GN evaluation and treatment) ^[33] Senior notes: Adrian Lui Pediatrics Notes.pdf (p326–327 — RPGN crescent formation, chronic GN) ^[34] Senior notes: Block A - Renal Replacement Therapies.pdf (p36 — Long-term transplant complications including recurrence of primary disease)

High Yield Summary

Definition: MPGN is a histological pattern (not a single disease) defined by mesangial proliferation + GBM thickening/duplication ("tram-track") on light microscopy.

Modern Classification (pathogenesis-based):

Immune complex-mediated MPGN (IF: Ig + C3) — caused by HCV, HBV, SLE, cryoglobulinaemia, MGRS/myeloma, infective endocarditis
Complement-mediated / C3 Glomerulopathy (IF: C3 dominant, Ig-negative) — subdivided into C3GN and DDD; caused by alternative complement pathway dysregulation (C3NeF, Factor H/I mutations)

Clinical Presentation: Mixed nephrotic-nephritic picture. Proteinuria (++), haematuria (+), nephrotic (++), nephritic (+), ARF (+), CRF (+). Can present as any glomerular syndrome.

Key Diagnostic Clue: Persistently low C3 > 8 weeks (unlike PSGN which normalizes by 8 weeks) — think MPGN or lupus nephritis.

Complement Pattern:

IC-MPGN (classical pathway): ↓C3, ↓C4
C3G (alternative pathway): ↓↓C3, normal C4

Must-Exclude Causes in HK: HCV (with cryoglobulins), HBV, SLE, monoclonal gammopathy (especially in older patients).

Histology Hallmarks: Tram-track GBM (LM), lobular accentuation (LM), IF pattern determines subtype, DDD has intramembranous dense deposits (EM).

Renal biopsy is essential for definitive diagnosis and to guide treatment.

High Yield Summary — Differential Diagnosis of MPGN

The clinical presentation of MPGN (mixed nephrotic-nephritic with low complement) must be differentiated from: PSGN, lupus nephritis, IgA nephropathy, cryoglobulinaemia, ANCA vasculitis, anti-GBM disease, membranous nephropathy, and MCD/FSGS.
Complement levels are the most powerful bedside discriminator:
- ↓C3 only → PSGN (transient), C3G, infective endocarditis GN
- ↓C3 + ↓C4 → Lupus, IC-MPGN, cryoglobulinaemia
- Normal complement → IgA nephropathy, ANCA vasculitis, anti-GBM, MCD, FSGS, membranous
Persistent low C3 > 8 weeks → think MPGN or lupus nephritis, NOT PSGN
Once MPGN pattern is confirmed on biopsy, IF determines the category:
- Ig + C3 → Immune complex-mediated → search for HCV, HBV, SLE, cryoglobulinaemia, MGRS
- C3-dominant → C3 Glomerulopathy → complement studies (C3NeF, Factor H, genetic testing)
In elderly patients with MPGN: always screen for monoclonal gammopathy (SIEP, UIEP, serum free light chains)
Renal biopsy (LM/IF/EM) is essential for definitive diagnosis and to guide treatment

High Yield Summary — Diagnosis of MPGN

MPGN is a histopathological diagnosis — there are no standalone clinical diagnostic criteria. Definitive diagnosis requires renal biopsy with LM/IF/EM.
Clinical clues raising suspicion: Mixed nephrotic-nephritic picture + persistently low C3 (> 8 weeks) + active urine sediment.
Pre-biopsy workup (mnemonic "CAVE HIM"): Complement, Autoantibodies, Viral serology, Electrophoresis/paraprotein, History of infection, Immunoglobulins/cryoglobulins, Malignancy screen.
IF is the KEY discriminator on biopsy:
- Ig + C3 → Immune complex-mediated → hunt for HCV, HBV, SLE, cryoglobulinaemia, MGRS
- C3-dominant → C3 Glomerulopathy → complement studies (C3NeF, Factor H, genetics)
EM subclassifies C3G: DDD (intramembranous dense deposits) vs C3GN (variable location deposits).
Do NOT forget paraprotein screen in elderly patients — MGRS is treatable and commonly missed.
Complement pattern:
- ↓C3, ↓C4 = classical pathway = IC-MPGN, lupus, cryoglobulinaemia
- ↓↓C3, normal C4 = alternative pathway = C3 Glomerulopathy
- Transient ↓C3 (normalizes ≤ 8 wk) = PSGN

High Yield Summary — Management of MPGN

The overarching principle: TREAT THE UNDERLYING CAUSE. MPGN management is not one-size-fits-all.
Supportive care for ALL patients:
- ACEI/ARB (anti-proteinuric, renoprotective — for ALL glomerulopathies)
- Low sodium diet + diuretics (frusemide ± thiazide ± spironolactone) for oedema
- Statins if persistent hyperlipidaemia
- DVT prophylaxis
- Monitoring: I/O, BP, body weight (aim ~1 kg/day loss), urine dipstick, serial RFT
Cause-specific treatment:
- HCV → DAAs ± rituximab ± plasmapheresis
- HBV → Entecavir/TAF (always before immunosuppression)
- SLE → HCQ + steroids + MMF/cyclophosphamide
- MGRS → Clone-directed therapy
- IE → Prolonged antibiotics
- Idiopathic → Steroids ± cyclophosphamide if deteriorating RFT
C3 Glomerulopathy: Supportive + immunosuppression (MMF/steroids) for progressive disease; eculizumab for refractory cases; emerging complement-targeted therapies (Factor B inhibitors).
Prognosis: poor — 50% ESRD at 10 years. High transplant recurrence especially for DDD ( > 80%) and C3GN (~50–70%).
Never combine ACEI + ARB. Never immunosuppress HBV patients without antivirals. Never give NSAIDs to patients with renal impairment.

High Yield Summary — Complications of MPGN

CKD → ESRD is the most important long-term complication: 50% reach ESRD within 10 years. CKD complications include fluid retention, metabolic acidosis, hypertension, anaemia, secondary hyperparathyroidism, and bone disease.
Crescentic transformation (RPGN) can cause loss of renal function in days to weeks. Cellular crescents may respond to immunosuppression; fibrous crescents are irreversible. Early treatment is critical.
Thromboembolic complications (renal vein thrombosis, DVT, PE) arise from loss of AT III in urine + hepatic overproduction of clotting factors. DVT prophylaxis for all high-risk nephrotic patients.
Infection from loss of immunoglobulins + immunosuppressive therapy. Pneumococcal vaccination for ALL nephrotic patients. PCP prophylaxis with cyclophosphamide/rituximab. Meningococcal vaccination before eculizumab.
Cardiovascular disease from hyperlipidaemia, hypertension, and chronic inflammation. Long-term risk modification essential.
Post-transplant recurrence is very high, especially for DDD ( > 80%) and C3GN (~50–70%). The complement defect is systemic, not kidney-intrinsic.

Membranoproliferative Glomerulonephritis

Membranoproliferative Glomerulonephritis (MPGN)

2. Epidemiology

3. Anatomy and Function Review

4. Etiology

A. Immune Complex-Mediated MPGN (IF: Ig + Complement)

5. Pathophysiology — Linking Etiology to Histology to Clinical Features

6. Classification

7. Clinical Features

9. Histopathological Features (Essential for Understanding)

Active Recall - Membranoproliferative Glomerulonephritis

Differential Diagnosis of MPGN

Approach by Complement Level

The Major Differentials — Explained From First Principles

Active Recall - DDx of MPGN

References

Diagnostic Criteria, Algorithm & Investigations for MPGN

2. The Diagnostic Algorithm — Step by Step

4. Investigation Modalities — Detailed Breakdown

Active Recall - Diagnosis of MPGN

References

Management of MPGN

1. Supportive Care — For ALL Patients With MPGN

2. Cause-Specific Treatment — The Critical Layer

4. Management of Specific Complications

Active Recall - Management of MPGN

References

Complications of MPGN

Metabolic Consequences of CKD (Explained)

Specific Thromboembolic Complications

Active Recall - Complications of MPGN

References

On this page

Membranoproliferative Glomerulonephritis

1. Definition

2. Epidemiology

Global Epidemiology

Hong Kong / East Asian Context

Trends

3. Anatomy and Function Review

The Glomerular Filtration Barrier (3 layers)

Mesangium

Complement System (Critical for understanding MPGN)

4. Etiology

Modern Classification Framework (Pathogenesis-Based)

A. Immune Complex-Mediated MPGN (IF: Ig + Complement)

i. Infections (Most important cause globally and in HK)

ii. Autoimmune Diseases

iii. Monoclonal Gammopathy / Paraprotein-Related

iv. Idiopathic Immune Complex MPGN

B. Complement-Mediated MPGN (C3 Glomerulopathy)

5. Pathophysiology — Linking Etiology to Histology to Clinical Features

Step-by-Step Pathogenesis

Why MPGN Is a "Mixed Nephrotic-Nephritic" Disease

Complement Levels — A Key Diagnostic Clue

6. Classification

Historical (EM-Based) Classification — For Reference

Modern (Pathogenesis-Based) Classification (2012–present) [Preferred]

By Primary vs Secondary

7. Clinical Features

A. Symptoms (with pathophysiological basis)

B. Signs (with pathophysiological basis)

C. Urinalysis Findings

8. Summary of Clinical Syndromes in MPGN

9. Histopathological Features (Essential for Understanding)

Light Microscopy (LM)

Immunofluorescence (IF) — The Key Discriminator

Electron Microscopy (EM)

10. Key Pathological Terms Review

Active Recall - Membranoproliferative Glomerulonephritis

References

Framing the Differential

Level 1: DDx of the Clinical Syndrome (Mixed Nephrotic-Nephritic Features with Low Complement)

The Major Differentials — Explained From First Principles

1. Post-Streptococcal Glomerulonephritis (PSGN)

2. Lupus Nephritis (SLE)

3. IgA Nephropathy

4. Cryoglobulinaemia (Often HCV-Associated)

5. ANCA-Associated Vasculitis (Pauci-Immune GN)

6. Anti-GBM Disease (Goodpasture Syndrome)

7. Membranous Nephropathy

8. Minimal Change Disease (MCD) and Focal Segmental Glomerulosclerosis (FSGS)

9. Monoclonal Gammopathy of Renal Significance (MGRS) / Multiple Myeloma

Level 2: DDx of the MPGN Histological Pattern (Once Biopsy Is Done)

Summary Table of Key Differentials

Systematic Diagnostic Algorithm for Approaching a Case

Differential Diagnosis in Paediatric vs Adult Settings

Active Recall - DDx of MPGN

1. Diagnostic Criteria — First Principles

2. The Diagnostic Algorithm — Step by Step

Step 1: Recognize the Clinical Syndrome

Step 2: Basic Laboratory Investigations

Step 3: Complement Levels — The Critical Fork in the Road

Step 4: Serological Workup

Step 5: Renal Biopsy — The Definitive Step

Step 6: Post-Biopsy Classification

3. Complete Diagnostic Algorithm (Mermaid Diagram)

4. Investigation Modalities — Detailed Breakdown

A. Urinalysis (Bedside + Lab)

B. Blood Tests — Basic Panel

C. Complement Studies — The Cornerstone

D. Serological Workup — Systematic Exclusion of Secondary Causes

E. Imaging

F. Renal Biopsy — The Gold Standard

5. Interpreting the Biopsy — A Decision Tree

6. Summary of Key Investigations and Their Rationale

Active Recall - Diagnosis of MPGN

Core Management Principle — Treat the Cause, Not Just the Pattern

Management Algorithm Overview

1. Supportive Care — For ALL Patients With MPGN

A. Monitoring

B. Anti-Oedema Measures

C. Anti-Proteinuric Therapy — ACEI/ARB