Physiologic vs Pathologic Jaundice
Physiologic jaundice: caused by immature hepatic conjugation capacity, increased fetal hemoglobin breakdown, and limited gut flora reducing bilirubin excretion. Onset: day 2–3 in term infants (NOT within first 24 hours). Peaks day 3–5. Resolves by day 10 (term) or week 2–3 (preterm). Bilirubin usually <15 mg/dL term infant. Pathologic jaundice (requires workup): jaundice within first 24 hours of life (always pathologic), rise >5 mg/dL/day, total bilirubin >15 mg/dL in term infant, direct (conjugated) bilirubin >1 mg/dL or >20% of total, jaundice persisting >2 weeks (term) or 3 weeks (preterm). Causes of early pathologic jaundice: Hemolytic disease of the newborn (HDN) — ABO incompatibility (most common), Rh incompatibility (most severe — maternal anti-D antibodies cross placenta → fetal hemolysis). G6PD deficiency. Congenital infections (TORCH). Breast milk jaundice: benign; peaks week 2–3; mechanism unclear (beta-glucuronidase in breast milk increases enterohepatic circulation); continue breastfeeding.
Diagnosis and Phototherapy
Diagnosis: total serum bilirubin (TSB) plotted on hour-specific Bhutani nomogram (risk zones). Direct (conjugated) bilirubin: elevated in conjugation defects (biliary atresia, Alagille syndrome, neonatal hepatitis) — always pathologic. Coombs test (DAT): positive in HDN (maternal antibodies coating infant RBCs). Phototherapy: blue light (420–490nm wavelength) converts insoluble unconjugated bilirubin to water-soluble photoisomers that bypass hepatic conjugation and are excreted in bile/urine without conjugation. Thresholds (AAP): based on gestational age, age in hours, and risk factors (isoimmune hemolytic disease, G6PD deficiency, sepsis, low gestational age). Exchange transfusion (double-volume exchange): replaces ~85% of infant's blood with donor blood — removes antibody-coated RBCs, bilirubin, and maternal antibodies. Indicated when phototherapy fails, or bilirubin approaching kernicterus threshold, or hydrops fetalis.
Kernicterus and Rh Incompatibility
Kernicterus (bilirubin encephalopathy): unconjugated bilirubin crosses BBB → deposits in basal ganglia, hippocampus, brainstem. Acute: hypotonia → hypertonia, high-pitched cry, opisthotonus (arching), seizures, coma. Chronic (irreversible): athetoid cerebral palsy, sensorineural hearing loss, upward gaze palsy, intellectual disability. Prevention: phototherapy and exchange transfusion per AAP guidelines. Rh incompatibility: Rh-negative mother + Rh-positive fetus. First pregnancy: maternal exposure to Rh+ fetal blood during delivery → IgG anti-D production (sensitization). Subsequent pregnancies: anti-D IgG crosses placenta → severe hemolysis. Prevention: Rh-immune globulin (RhoGAM) 300 mcg IM given to ALL Rh-negative mothers at 28 weeks AND within 72 hours of delivery. Also after amniocentesis, abortion, or any feto-maternal hemorrhage. Hydrops fetalis: severe Rh incompatibility → fetal anemia + heart failure + anasarca (generalized edema) + pleural effusions + ascites.