Expansion
High red cell turnover with immature conjugation and enterohepatic recycling
Expansion
Newborns are predisposed because of:
- High red cell mass with a shorter lifespan (about 70 to 90 days)
- Immature UDP-glucuronosyltransferase, so conjugation is limited
- Increased enterohepatic circulation: gut beta-glucuronidase deconjugates bilirubin, which is then reabsorbed, and the sterile gut lacks bacteria to convert it to urobilinogen
Timing is the key to diagnosis
- Under 24 hours: always pathological. Haemolysis (rhesus or ABO incompatibility, G6PD, spherocytosis) or congenital infection
- 24 hours to 2 weeks: usually physiological, or breastfeeding-associated, bruising, polycythaemia, or sepsis
- Over 2 weeks (prolonged): needs split bilirubin. Conjugated jaundice is always pathological and demands urgent exclusion of biliary atresia, for which surgery before 60 days greatly improves outcome. Unconjugated causes include breast milk jaundice, hypothyroidism and Gilbert syndrome
Kernicterus occurs because unconjugated bilirubin is lipid soluble and crosses the immature blood-brain barrier, depositing in the basal ganglia. Risk is increased by prematurity, acidosis, sepsis and drugs displacing bilirubin from albumin.