Neonatal jaundice assessment

Neonatal Jaundice: Physiology, Classification & Differential Diagnosis

Jaundice occurs in approximately 60% of term and 80% of preterm infants during the first week of life, resulting from the accumulation of unconjugated (indirect) or conjugated (direct) bilirubin in the skin, sclerae, and subcortical tissues.

Bilirubin Metabolism in the Neonate

Neonatal hyperbilirubinaemia results from a combination of physiological phenomena:

1. Accelerated bilirubin production: Neonates have a higher haematocrit ($50\%\text{ to }65\%$) and a shortened red blood cell lifespan (70 to 90 days vs 120 days in adults), generating 2 to 3 times more bilirubin per kilogram per day.
2. Immature hepatic conjugation: Hepatic uridine diphosphate glucuronosyltransferase (UGT1A1) activity is $< 1\%$ of adult levels at birth, reaching adult competence by 6 to 14 weeks.
3. Increased enterohepatic circulation: High intestinal mucosal levels of $\beta$-glucuronidase deconjugate bilirubin diglucuronide into lipid-soluble unconjugated bilirubin, which is reabsorbed into the portal circulation, exacerbated by delayed meconium passage.

Physiological vs. Pathological Early Jaundice

• Physiological Jaundice:
  • Onset: Always appears after 24 hours of life (typically days 2 to 3).
  • Peak: Peaks at days 3 to 5 in term infants (levels rarely exceed $200\text{ to }250\text{ umol/L}$).
  • Resolution: Resolves spontaneously by day 10 to 14 in term infants (day 21 in preterm infants).
  • Characteristics: Purely unconjugated hyperbilirubinaemia; infant is alert, feeds vigorously, has normal wet nappies, and normal pigmented yellow-mustard stools.
• Pathological Jaundice in the First 24 Hours:
  • Any jaundice visible within the first 24 hours of life is pathological until proven otherwise.
  • Major Etiologies:
    • ABO haemolysis: Group O maternal antibodies can affect a group A or B infant. DAT may be positive or negative; interpret blood groups, haemoglobin, reticulocytes and bilirubin together. DAT alone cannot exclude the diagnosis.
    • Rhesus (Rh) Isoimmunisation: Severe haemolytic disease of the newborn. Occurs when a non-sensitized Rh(D)-negative mother carries an Rh(D)-positive fetus and develops anti-D IgG antibodies following fetomaternal haemorrhage. In subsequent Rh(D)-positive pregnancies, maternal anti-D antibodies cause profound fetal haemolysis, hydrops fetalis, severe early neonatal jaundice, and hepatosplenomegaly. DAT is strongly positive.
    • Red Cell Enzymopathies: Glucose-6-phosphate dehydrogenase (G6PD) deficiency (X-linked recessive; common in Mediterranean, African, Middle Eastern, and Asian populations; acute haemolysis triggered by oxidative stress, naphthalene mothballs, or infection) and pyruvate kinase deficiency.
    • Red Cell Membrane Defects: Hereditary spherocytosis (autosomal dominant spectrin/ankyrin defect; positive family history, spherocytes on blood film, negative DAT).
    • Congenital TORCH Infections & Neonatal Sepsis: Toxoplasmosis, Rubella, Cytomegalovirus, Herpes simplex, Syphilis, Listeria, or bacterial sepsis (Group B Streptococcus, Escherichia coli).
  • Mandatory Immediate Investigations:
    • Serum total and conjugated bilirubin.
    • Maternal and infant blood group and Rh(D) status.
    • Direct Antiglobulin Test (DAT / Direct Coombs test).
    • Full blood count, blood film (reticulocytosis, spherocytes, bite cells), and reticulocyte count.
    • Serum CRP, blood cultures, and maternal serology review if infection suspected.

Prolonged Neonatal Jaundice (> 14 Days in Term, > 21 Days in Preterm)

When jaundice persists beyond 14 days in term infants or 21 days in preterm infants, immediate clinical evaluation is mandatory. The critical first step is fractionating serum bilirubin into conjugated (direct) and unconjugated (indirect) components.

1. Conjugated (Cholestatic) Hyperbilirubinaemia

• Conjugated bilirubin: A direct/conjugated result above about 17 micromol/L is concerning in an infant irrespective of whether it reaches 20% of total bilirubin. Investigate cholestasis rather than diagnosing breast-milk jaundice.
• Clinical Hallmarks: Pale, clay-coloured (acholic) stools (absence of stercobilin), dark yellow/tea-coloured urine (water-soluble conjugated bilirubin filtered into urine), firm hepatomegaly, and failure to thrive.
• Biliary Atresia (The Critical Surgical Emergency):
  • Progressive, idiopathic inflammatory fibro-obliteration of the extrahepatic biliary tree, leading to biliary cirrhosis, portal hypertension, and hepatic failure.
  • Incidence in Australia: ~1 in 15,000 live births.
  • Diagnostic Workup:
    1. Urgent high-resolution abdominal ultrasound: Demonstrates absent or atretic gallbladder, absent common bile duct, and the "triangular cord sign" (echogenic fibrous ductal remnant anterior to the portal vein bifurcation).
    2. Percutaneous liver biopsy: Demonstrates portal tract expansion, bile ductular proliferation, and bile plugs.
    3. Operative cholangiogram: Gold standard confirming non-patent extrahepatic biliary tree.
  • Surgical Intervention: Kasai portoenterostomy (hepatoportoenterostomy)—excision of the atretic extrahepatic biliary fibrous remnant and anastomosis of a jejunal Roux-en-Y loop directly to the exposed transected liver hilum to drain microscopic bile ductules.
  • Time matters: Earlier Kasai surgery generally improves bile-drainage outcomes, so cholestasis needs urgent referral. Increasing age worsens prognosis, but no single age makes success impossible or transplantation inevitable; the specialist team assesses the individual infant.
• Other Causes of Cholestasis: Choledochal cyst (dilatation of biliary tree; cystic mass on ultrasound), alpha-1-antitrypsin deficiency (PiZZ phenotype), cystic fibrosis, galactosemia, parenteral nutrition-associated cholestasis (PNAC), and neonatal giant cell hepatitis.

2. Unconjugated Prolonged Hyperbilirubinaemia

• Breast Milk Jaundice:
  • Highly prevalent benign condition affecting up to 20% to 30% of healthy, exclusively breastfed infants.
  • Mechanism: Substances in maternal breast milk (including $\beta$-glucuronidase, non-esterified free fatty acids, and pregnane-$3\alpha,20\beta$-diol) inhibit infant hepatic UGT1A1 activity and increase intestinal deconjugation and enterohepatic reabsorption.
  • Clinical Course: Onset late in the first week of life, peaking in weeks 2 to 3, and gradually resolving over 3 to 12 weeks.
  • Management: Infant is alert, thriving, gaining weight appropriately, with normal yellow-gold stools and clear urine. It is a diagnosis of exclusion (after ruling out cholestasis, hypothyroidism, and infection). Breastfeeding must NOT be discontinued; provide parental reassurance.
• Breastfeeding (Under-Feeding) Jaundice:
  • Occurs in the first week of life due to inadequate caloric and fluid intake (poor latch, delayed lactogenesis II).
  • Mild dehydration, weight loss $> 10\%$ of birth weight, delayed meconium clearance, and increased enterohepatic circulation. Managed by lactation support, increasing feeding frequency (8 to 12 times per day), and supplementation if indicated.
• Congenital Hypothyroidism:
  • Leads to prolonged unconjugated hyperbilirubinaemia via delayed maturation of hepatic glucuronide transferase.
  • Associated signs: lethargy, poor feeding, severe constipation, coarse facial features, large anterior and posterior fontanelles, umbilical hernia, macroglossia, and hypotonia. Screened universally on newborn bloodspot.
• Urinary Tract Infection (UTI) / Occult Sepsis:
  • Gram-negative bacterial endotoxins (E. coli) cause haemolysis and impaired canalicular bilirubin transport. Screen prolonged jaundice with urine microscopy and culture.

Primary references (checked 7 October 2026): ANZCOR newborn ventilation.