What are typical bilirubin levels for a 5-week-old infant?

Typical Bilirubin Levels for 5-Week-Old Infants

By 5 weeks of age, healthy term infants should have resolved their physiologic jaundice, with bilirubin levels typically below 1-2 mg/dL, similar to normal adult values. 1, 2

Normal Physiologic Timeline

• Physiologic jaundice in healthy term newborns typically resolves by 1-2 weeks of age, making any clinically apparent jaundice or elevated bilirubin at 5 weeks (35 days) abnormal and requiring investigation. 2

• In breastfed infants, approximately one-third may still be clinically jaundiced at 2 weeks of age (with two-thirds having biochemical jaundice), but this should resolve shortly thereafter. 3

• Any infant who remains jaundiced beyond 3 weeks of age must have measurement of both total and direct/conjugated bilirubin to identify potential cholestasis or other pathologic causes. 4, 2

When to Investigate at 5 Weeks

Immediate Evaluation Required If:

• Total bilirubin remains elevated above normal adult ranges (typically >1-2 mg/dL warrants investigation at this age). 1, 2

• Direct/conjugated bilirubin exceeds 1.0 mg/dL when total bilirubin is ≤5 mg/dL, which is considered abnormal. 4, 2

• The infant has pale stools or dark urine, suggesting cholestasis. 3

Essential Workup for Persistent Jaundice at 5 Weeks:

• Measure both total and direct/conjugated bilirubin to differentiate unconjugated from conjugated hyperbilirubinemia. 4, 2

• Verify newborn thyroid screening results, as congenital hypothyroidism causes indirect hyperbilirubinemia. 4, 2, 3

• Check galactosemia screening results. 4, 2

• Assess stool and urine color—pale stools or dark urine indicate possible biliary obstruction. 3

Critical Pathologic Causes to Consider

Conjugated hyperbilirubinemia at this age suggests:

• Biliary atresia (time-sensitive diagnosis requiring urgent surgical evaluation). 2, 3

• Cholestatic liver disease. 4, 2

• Metabolic disorders. 2

Unconjugated hyperbilirubinemia persisting at 5 weeks suggests:

• Hypothyroidism. 2, 3

• Hemolytic disorders (including G6PD deficiency, which can present with late-rising bilirubin). 2, 3

• Breast milk jaundice (diagnosis of exclusion after ruling out pathologic causes). 3, 5

Common Pitfalls

• Do not assume prolonged jaundice is simply "breast milk jaundice" without proper evaluation—this is a diagnosis of exclusion only after measuring direct bilirubin and ruling out serious causes. 3

• Visual estimation of jaundice is unreliable, particularly in darkly pigmented infants; always obtain laboratory measurement. 4, 2

• Laboratory measurement of direct bilirubin can vary widely between laboratories, so interpret results in clinical context. 4, 6

• Any infant jaundiced beyond 3 weeks requires direct bilirubin measurement—missing biliary atresia can result in irreversible liver damage. 4, 2, 3

Clinical Assessment

• Verify the infant is feeding well with adequate output and appropriate weight gain to ensure adequate bilirubin elimination. 1

• Assess for signs of dehydration, as adequate hydration helps with bilirubin excretion. 1

• Check for any neurologic signs that might suggest previous bilirubin toxicity, though this would be unusual if the infant has been appropriately monitored. 2