MECHANISM:
- High rate of bilirubin production and an impaired ability to extract bilirubin from the body.
- Bilirubin production also is increased as a result of elevated hematocrit and RBC volume per body weight and a shorter life span of the RBCs (70–90 days).
- Infants have immature hepatic uridine-diphosphoglucuronic glucuronosyltransferase (UDPGT), a key enzyme involved in the conjugation of bilirubin that facilitates excretion from the body.
DIAGNOSTIC CRITERIA IN THE FULL TERM
- Unconjugated hyperbilirubinemia that occurs after the first postnatal day.
- It can last up to 1 week.
- The TSB concentration peaks at approximately 5.5 mg/ dL (94.1 μmol/L) by the third postnatal day.
- By 96 h of age, 95 % of infants have TSB concentrations of less than 12 mg/dL.
- Bilirubinemia > 17 mg/dL is not physiologic
- It usually fades by 7-14 days (by 3 weeks in preterm infants).
- No accompanied anemia
- The baby looks healthy
- Urine & stools are normal.