# Neonatal Jaundice > Neonatal jaundice for FMGE Paediatrics: physiological vs pathological rules, phototherapy and exchange thresholds, haemolysis work-up and kernicterus. - Canonical URL: https://prepelephant.com/topics/fmge/paediatrics/neonatal-jaundice-fmge - Exam / course: FMGE · Subject: Paediatrics - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Neonatal Jaundice", PrepElephant, https://prepelephant.com/topics/fmge/paediatrics/neonatal-jaundice-fmge ## Direct answer Jaundice in a newborn becomes pathological — and a haemolytic emergency until proved otherwise — when it appears within 24 hours of birth, exceeds about 15 mg per dL in a term baby, rises faster than 5 mg per dL per day, persists beyond two weeks in a term or three in a preterm infant, or when the conjugated fraction exceeds 2 mg per dL. Thresholds are read off gestation- and age-specific nomograms: roughly 15 mg per dL for phototherapy and the low twenties for exchange transfusion in a well term baby, lower for preterm, sick or haemolysing infants. ## What you must remember - Physiological jaundice peaks on day 3–5 at about 5–6 mg per dL in term infants (8–12 in preterms), never appears in the first 24 hours, and clears within two weeks in term babies. - The five pathological rules: onset under 24 hours, level above 15 mg per dL (term), rise above 5 mg per dL per day, persistence beyond 14 days (term) or 21 (preterm), and conjugated bilirubin above 2 mg per dL or a fifth of the total. - Day-one jaundice means haemolysis — ABO incompatibility (mother O, baby A or B), Rh incompatibility, G6PD deficiency or infection; direct Coombs test, blood groups and a reticulocyte count come first. - Prolonged unconjugated jaundice that is benign: breast milk jaundice, from the second or third week in a thriving baby, occasionally high but rarely needing more than monitoring — after hypothyroidism and galactosaemia are excluded. - Conjugated hyperbilirubinaemia with pale stools and dark urine means cholestasis — biliary atresia, and the Kasai operation works best before 60 days of life; phototherapy does not help. - Unbound unconjugated bilirubin crossing into the basal ganglia causes kernicterus: lethargy, poor feeding, a high-pitched cry, then opisthotonus and seizures, leaving athetoid cerebral palsy and deafness. - Phototherapy converts bilirubin to water-soluble photoisomers through skin; complications are loose stools, rash, dehydration and "bronze baby" discolouration with cholestasis — eyes and nappy area are shielded. - Exchange transfusion, double volume (about 160 mL per kg) through the umbilical vein, is for babies exceeding exchange thresholds or rising fast with haemolysis despite intensive phototherapy. ## Approach to a jaundiced newborn, in order A term baby on day 3, jaundiced to the knees, total bilirubin 17.5 mg per dL. First decide physiological or not: the level crosses the phototherapy line for his age, so this is pathological until excluded. Second, assess for haemolysis: mother group O, baby B, a spleen tip — send a direct Coombs test, reticulocytes, smear and G6PD assay, and check the conjugated fraction. Third, treat while awaiting results: intensive phototherapy with maximal skin exposure, supplemented feeds to drive stooling, and a repeat bilirubin in 4–6 hours to establish the trajectory. Had the level been 24 at 48 hours in a Coombs-positive Rh baby, you would prepare a double-volume exchange now. A four-week-old with mild jaundice but chalky stools and yellow urine forks the pathway entirely — direct hyperbilirubinaemia, ultrasound and scintigraphy, urgent surgical referral for biliary atresia, where every week of delay costs bile duct patency. ## The trap that costs marks The classic error is treating the label rather than the trajectory: 14 mg per dL on day 5 in a thriving breastfed term baby sits below the line, while the same 14 at 20 hours is a haemolytic emergency — the number is identical, the nomogram is not, because thresholds fall with every hour of age and week of prematurity. The second error is reassuring parents about prolonged jaundice without splitting the fraction: a "breast milk jaundice" label hiding a direct fraction of 3 mg per dL means biliary atresia, and the operative window closes at 60 days. Finally, remember G6PD — sudden severe jaundice in a male baby after maternal sulfa or naphthalene (mothballs) exposure is a viva favourite. ## Frequently asked questions ### Which features distinguish pathological from physiological jaundice? Onset within 24 hours, total bilirubin above 15 mg per dL, a rise over 5 mg per dL per day, persistence beyond 14 days (term) or 21 days (preterm), or conjugated bilirubin above 2 mg per dL. ### When is exchange transfusion considered in a term baby? When total bilirubin approaches the low twenties on the age-specific nomogram, or earlier with haemolysis, prematurity or signs of acute bilirubin encephalopathy. ### What causes jaundice within the first 24 hours of life? Haemolysis — ABO or Rh incompatibility, G6PD deficiency — plus congenital infection; Coombs test and blood groups come first. ### What is breast milk jaundice? Prolonged unconjugated hyperbilirubinaemia from the second or third week in a thriving breastfed baby, often reaching high levels but rarely needing treatment; breastfeeding is not stopped. ### Why is phototherapy ineffective in biliary atresia? The problem is excretion, not metabolism — conjugated pigment cannot be photoisomerised away, and definitive treatment is early hepatoportoenterostomy. ### What are the early signs of kernicterus? Lethargy, poor sucking, a high-pitched cry and hypotonia progressing to retrocollis, opisthotonus and seizures — an emergency mandating exchange transfusion.