Baby Amanda was born at 37 weeks, birth weight 2.8 kg, no complications, started breastfeeding. She appears mildly yellow from 48 hours of life with a weight loss of 8% but otherwise normal examination. ^[1]

This case anchors the lecture: a near-term baby with onset at 48 hours, mild jaundice and 8% weight loss. It may fit transitional jaundice with suboptimal intake, but the actual TSB, hour of life, feeding assessment and weight/output trajectory determine follow-up and treatment.

Bilirubin is the breakdown product of haem ^[1]

Haem (from RBC breakdown in reticuloendothelial system)
  ↓ Heme oxygenase
Biliverdin + CO
  ↓ Biliverdin reductase
Unconjugated bilirubin (HYDROPHOBIC)
  ↓ Binds albumin for transport
Liver (uptake by ligandin → conjugation by UDPGT)
  ↓
Conjugated bilirubin = bilirubin diglucuronide (HYDROPHILIC)
  ↓ Excreted into bile → gut
Gut bacteria convert to urobilinogen
  ↓
80-90% excreted: stercobilin (stool), urobilin (urine)
10-20% reabsorbed → enterohepatic circulation

Unconjugated bilirubin is hydrophobic → binds to albumin and is transported to the liver ^[1]

Why does this matter? Because unconjugated bilirubin is hydrophobic, it can cross lipid membranes including the blood-brain barrier (BBB). This is the fundamental reason kernicterus occurs. Conjugated bilirubin is water-soluble and cannot cross the BBB — hence conjugated hyperbilirubinemia does NOT cause kernicterus (but reflects serious hepatobiliary disease).

1. UPSTREAM: High Hb load in neonates (mean 17–19 g/dL) + Short RBC lifespan (half-life 80 days) ^[1]

Why? Fetal haemoglobin (HbF) has a higher oxygen affinity than adult HbA — this is necessary in utero to "steal" oxygen from maternal blood across the placenta. After birth, the neonate no longer needs HbF, so there is a massive wave of RBC destruction to replace HbF with HbA. This releases enormous quantities of haem. Additionally, neonatal RBCs have a shorter lifespan (~90 days vs ~120 days for adult RBCs), further increasing haem turnover.

2. DOWNSTREAM: Immature liver metabolic function

• Low ligandin (uptake of bilirubin into liver cells)
• Low conjugation enzyme activity (UDPGT) ^[1]

Why? Ligandin supports hepatocyte uptake, while UDPGT/UGT1A1 conjugates bilirubin with glucuronic acid so it can be excreted. Both functions are developmentally immature in the newborn; maturation is gradual rather than a switch at a fixed age.

3. ENTEROHEPATIC CIRCULATION — "recycling" of bilirubin from gut to blood, especially when feeding is minimal in the first 2–3 days of life ^[1]

Why? In the neonatal gut:

• The gut is relatively sterile (no gut flora to convert bilirubin to urobilinogen for excretion)
• β-glucuronidase in the intestinal brush border deconjugates bilirubin diglucuronide back to unconjugated bilirubin
• This unconjugated bilirubin is reabsorbed into the portal circulation → sent back to the liver
• When feeding is minimal (first 2–3 days), intestinal transit is slow → more time for reabsorption

UDPGT genetic variation (polymorphism) common — affects activity

• Common: Gilbert syndrome
• Uncommon: Crigler-Najjar syndrome ^[1]

^[1][5]

Unconjugated bilirubin is hydrophobic → can cross lipid layers and blood-brain barrier → causes damage to neural tissue Most unconjugated bilirubin is bound to albumin (protective) Risk is higher when "free" bilirubin is high:

• When albumin is low
• When there is competitive binding to albumin, e.g. drugs ^[1]

"Free" unconjugated bilirubin (not bound to albumin) is the neurotoxic fraction. The gross brain photograph illustrates the yellow staining that gave kernicterus its name, classically involving the globus pallidus/subthalamic nuclei and brainstem auditory pathways.

Risks of kernicterus higher when:

• Very high unconjugated bilirubin level in blood for a prolonged period
• High "free" bilirubin
• Haemolysis
• Sepsis
• Acidosis
• Hypoglycaemia
• Prematurity ^[1]

Why each factor increases risk:

• Haemolysis: produces bilirubin faster than the liver can clear it, leading to very high levels
• Sepsis: opens the BBB (inflammation increases permeability), impairs hepatic function
• Acidosis: unconjugated bilirubin binds albumin less tightly at low pH → more free bilirubin
• Hypoglycaemia: brain already metabolically stressed → more susceptible to bilirubin toxicity
• Prematurity: lower albumin levels, more immature BBB, less mature hepatic conjugation

Early: hypotonia, poor feeding, lethargy, hypertonia, opisthotonus, fever, convulsion, death Late: extrapyramidal signs (dystonic cerebral palsy), hearing loss (SNHL), upward gaze palsy ^[1]

^[1][4]

History:

• Gestation, prenatal complications
• Birth weight
• Age of life
• Feeding details
• Blood groups / G6PD status
• Other postnatal complications e.g. infection ^[1]

Why each matters:

• Gestation: preterm infants are at higher risk (immature liver, lower albumin, more permeable BBB)
• Birth weight: low birth weight correlates with prematurity and smaller albumin reserves
• Age of life: visible jaundice in the first 24 hours requires urgent serum measurement and evaluation
• Feeding details: latch and milk transfer, frequency, urine/stool output, weight trajectory and supplementation—not feeding label alone
• Blood groups/G6PD: mother-baby Rh/ABO incompatibility? Hong Kong public hospitals routinely provide cord-blood screening for G6PD deficiency, but verify the individual result and remember that testing during/soon after haemolysis can be falsely normal. ^[14]
• Infection: sepsis worsens jaundice and increases kernicterus risk

Physical examination:

• Severity of jaundice – using transcutaneous bilirubinometer
• Hydration
• Pallor / plethora
• Cephalhematoma / bruises
• Neurologic state
• Size of liver and spleen ^[1]

Why each matters:

• Transcutaneous bilirubinometer: non-invasive screening; if above threshold → confirm with serum bilirubin
• Hydration: dehydration concentrates bilirubin and suggests inadequate feeding
• Pallor: suggests haemolysis (anaemia from RBC destruction)
• Plethora: suggests polycythaemia (more RBCs → more haem breakdown)
• Cephalhematoma/bruises: extravasated blood = extra source of haem for breakdown
• Neurologic state: looking for signs of acute bilirubin encephalopathy (lethargy, hypotonia/hypertonia, opisthotonus)
• Hepatosplenomegaly: may suggest haemolysis (extramedullary haematopoiesis), infection, or hepatobiliary disease

The slide photographs pair a scalp cephalhaematoma and extensive facial bruising to make the same visual point: both are reservoirs of extravasated blood, so bilirubin can continue to rise as that blood is broken down even without ongoing bleeding.

Lab test: TOTAL SERUM BILIRUBIN ^[1]

Total serum bilirubin (TSB) is the definitive measurement for treatment decisions. Fractionate bilirubin when jaundice is prolonged or cholestasis is suspected; a transcutaneous value is a screening measurement and should be confirmed with TSB according to the applicable threshold/protocol. ^[10][13]

Additional investigations depending on clinical picture:

• CBC + reticulocyte count + blood smear (haemolysis?)
• Blood grouping of mother and baby (ABO/Rh incompatibility?)
• Direct Coombs test (immune haemolysis?)
• G6PD assay
• LFT including conjugated bilirubin, ALT, AST, ALP, GGT, albumin
• Infection screen if sepsis suspected
• Thyroid function tests if jaundice prolonged

Treatment — Phototherapy:

• Photo-isomerisation of bilirubin to less toxic (hydrophilic) and readily excretable forms (in bile and urine)
• Wavelength 460 nm (BLUE light spectrum) The slide lists eye exposure, dehydration, rash and loose stool as practical concerns during treatment. ^[1]

Mechanism explained from first principles:

Unconjugated bilirubin is a tetrapyrrole with a specific stereochemistry (4Z,15Z configuration). When blue light (peak ~460 nm) hits the bilirubin molecules deposited in the skin:

1. Structural isomerisation → converts to lumirubin, which is water-soluble and can be excreted in bile and urine WITHOUT conjugation
2. Configurational isomerisation → converts from the 4Z,15Z form to the 4Z,15E form, which is also more water-soluble

This is why phototherapy works without the liver needing to do anything — it bypasses the conjugation bottleneck entirely.

Practical monitoring shown by the equipment photographs: expose as much skin as safely possible, use correctly fitted eye protection with routine eye care, maintain thermoregulation, and monitor hydration, weight, feeding and bilirubin response. Do not use sunlight as treatment. ^[13]

The deck's fixed “20 mg/dL” warning and its lower/medium/higher-risk graph reflect older guidance. Do not use either as a current treatment threshold. For infants ≥35 weeks, the 2022 AAP guideline uses separate hour-specific phototherapy and exchange-transfusion curves determined by:

• gestational age;
• postnatal age in hours;
• measured total serum bilirubin (do not subtract the direct fraction); and
• recognised neurotoxicity risk factors, including gestational age < 38 weeks, albumin < 3.0 g/dL, isoimmune haemolytic disease, G6PD deficiency/other haemolysis, sepsis, or significant clinical instability in the preceding 24 hours. ^[10]

Use the current local nomogram/protocol at the bedside; infants < 35 weeks require a neonatal-unit protocol. TSB—not visual colour or a fixed number—is the definitive test for phototherapy and escalation decisions. ^[10]

Exchange transfusion rapidly removes bilirubin, sensitised red cells and circulating antibody. ^[1]

Mechanism: Double-volume exchange transfusion removes approximately 85% of the baby's circulating RBCs and ~50% of the extravascular bilirubin. It simultaneously provides fresh albumin with binding capacity for remaining bilirubin. In immune haemolysis (Rh disease), it also removes the offending maternal antibodies and the antibody-coated neonatal RBCs.

The slide's fixed > 380 µmol/L criterion is outdated. Begin escalation of care when TSB is 2 mg/dL (34 µmol/L) below the infant's exchange threshold; provide intensive phototherapy, hydration and urgent neonatal consultation while preparing. Perform urgent exchange transfusion when TSB is at/above the applicable exchange threshold or the infant has intermediate/advanced acute bilirubin encephalopathy. ^[10]

Risks: arrhythmia/electrolyte disturbance, thrombocytopenia, infection, vascular complications, air embolism and necrotising enterocolitis; this is a neonatal intensive-care procedure.

The slide lists IVIg broadly for immune haemolysis. Current AAP guidance restricts it to infants with DAT-positive isoimmune haemolytic disease whose TSB reaches or exceeds the escalation-of-care threshold. Its benefit is uncertain and an association with necrotising enterocolitis has been reported, so intensive phototherapy, hydration, trajectory and ability to perform exchange transfusion must guide the decision. ^[10]

The slide defines conjugated hyperbilirubinaemia as direct bilirubin > 2 mg/dL (35 µmol/L) or > 15% of TSB; this is outdated. ^[1]

A direct bilirubin > 1.0 mg/dL (17 µmol/L) is abnormal and warrants timely cholestasis evaluation/referral. Requiring the direct fraction to exceed 15% or 20% of TSB can miss early disease and is no longer necessary. ^[10][12]

Associated with:

• Elevated parenchymal/ductal enzymes
• Deranged synthetic functions: e.g. clotting factors, albumin
• Deranged detoxification functions: e.g. hyperammonaemia
• Deranged metabolic function: e.g. hypoglycaemia ^[1]

Neonatal period:

• Neonatal hepatitis (etiological agents mostly unknown)
• Biliary atresia / choledochal cyst
• Metabolic diseases: e.g. citrin deficiency, galactosemia
• Parenteral nutrition associated cholestasis
• Syndromal disorders
• “Neonatal haemochromatosis” (historical phenotype; many cases are now recognised as gestational alloimmune liver disease) Beyond neonatal period:
• Viral hepatitis (A–E)
• Drug-induced hepatotoxicity (e.g. paracetamol)
• Wilson's disease
• Haemochromatosis, other metabolic diseases
• Others: choledochal cyst, hereditary hyperbilirubinemia
• Cystic fibrosis ^[1]

In neonatal period, RULE OUT obstructive jaundice — amenable to surgical treatment:

• Biliary atresia
• Choledochal cyst ^[1]

Progressive obliterative cholangiopathy due to ductal obstruction ^[1]

What happens: The extrahepatic (and sometimes intrahepatic) bile ducts undergo progressive inflammatory destruction and fibrosis, leading to complete obstruction of bile flow. The exact aetiology is unknown, but theories include perinatal viral infection triggering an autoimmune-mediated ductal injury, genetic susceptibility, and abnormal morphogenesis.

If untreated → bile accumulates → hepatocyte damage → progressive fibrosis → cirrhosis → portal hypertension → liver failure → death before age 2 without intervention. ^[4]

Present during or beyond neonatal period with:

• Prolonged jaundice
• Clay-colour stool
• Tea-colour urine
• Poor growth
• Enlarged (or shrunken) liver and spleen ^[1]

In the clinical photographs, the infant has obvious scleral icterus and a protuberant abdomen compatible with hepatomegaly. These are recognition cues only: palpation, growth assessment and fractionated bilirubin establish the clinical problem.

Why clay-coloured stool? No bilirubin reaches the gut (complete biliary obstruction) → no stercobilin → pale/clay/acholic stool. This is one of the most important clinical signs and should trigger urgent investigation.

Why tea-coloured urine? Conjugated bilirubin is water-soluble → spills into urine → dark urine.

Why poor growth? Bile is essential for fat absorption (bile salts emulsify dietary fats for lipase action). Without bile → fat malabsorption → calorie deficiency + fat-soluble vitamin deficiency (A, D, E, K).

Lab: Conjugated hyperbilirubinemia ^[1]

Additional findings: ↑GGT (characteristically high in biliary atresia — higher than in neonatal hepatitis), ↑ALP, ↑ALT/AST (but often not dramatically elevated), deranged coagulation (from vitamin K malabsorption).

^[4][8]

The slide states “before 12 weeks = best”; current teaching is more urgent: aim to diagnose and treat before 30–45 days whenever possible. ^[1][11]

The Kasai operation (portoenterostomy) involves:

1. Excising the fibrotic extrahepatic biliary remnant
2. Exposing the cut surface of the porta hepatis (where tiny residual bile ductules may exist)
3. Anastomosing a Roux-en-Y loop of jejunum directly to this cut surface

Why timing matters: ongoing cholangiopathy and fibrosis progressively reduce the chance of bile drainage and native-liver survival. Age is not an isolated automatic contraindication to Kasai; urgent multidisciplinary surgical/transplant assessment determines the best path. ^[11][12]

Outcome concept shown by the slide flowchart: bile drainage may clear, reduce or fail to improve jaundice. Even after initial clearance, jaundice can recur and chronic liver disease, cholangitis or portal hypertension may lead to transplant. Kasai can preserve the native liver for years; it should not be presented as either guaranteed cure or merely a temporary bridge.

The lecture flowchart (slide 41) shows three possible outcomes after Kasai portoenterostomy ^[1]:

• Jaundice clear → may remain cleared (best outcome) or recur → liver failure
• Jaundice reduced → progressive liver failure
• Jaundice persistent → liver failure
• All liver failure pathways → liver transplant

Indications for liver transplant referral:

• Progressive liver failure
• Growth retardation
• Recurrent cholangitis
• Portal hypertension ^[1]

BA remains the most common indication for paediatric liver transplant Results of LT for BA patients comparable to non-BA patients (~90% 5-to-10-year survival) Timely referral can reduce morbidity and mortality ^[1]

Historical HKU cohort shown in slides 43–46 (1993–2013): 113 recipients, LDLT:DDLT = 83:30, with approximately 90% 10-year survival; 76 recipients had BA. BA recipients had higher pre-transplant PELD/MELD scores (25.8 vs 8.2) but similar operative duration and comparable survival curves. These are valuable local historical outcomes, not current programme statistics or an individual prognostic estimate. ^[1]

Based on past papers and lecture emphasis:

1. MCQ: A 5-day-old term baby with unconjugated hyperbilirubinemia — which sign should prompt further investigation? → Answer: Pallor (suggests haemolysis) — from 2023 MCQ Q89. ^[2]

2. MCQ: A 1-month-old baby with clay-coloured stool, conjugated hyperbilirubinemia, US showing small gallbladder and non-visualised bile duct — most likely diagnosis? → Answer: Biliary atresia — from 2025 MCQ Q49. ^[3]

3. SAQ: Explain the physiology of neonatal jaundice → Three mechanisms: high Hb load + short RBC lifespan, immature liver (low ligandin + low UDPGT), increased enterohepatic circulation.

4. SAQ: Differentiate suboptimal-intake hyperbilirubinaemia from breast-milk jaundice → See Section 9.

5. SAQ: What are the clinical features and management of biliary atresia? → Persistent jaundice + acholic stool + dark urine + firm hepatomegaly; direct hyperbilirubinaemia; urgent referral and Kasai as early as possible (best outcomes before 30–45 days); transplant assessment for progressive liver disease/failed drainage.

6. SAQ: List the risk factors for kernicterus → Very high bilirubin, free bilirubin, haemolysis, sepsis, acidosis, hypoglycaemia, prematurity.

7. MCQ: A neonate with jaundice — which type of bilirubin does NOT cause kernicterus? → Answer: Conjugated bilirubin (water-soluble, cannot cross BBB).