A complete guide to jaundice in newborns — physiological vs pathological, bilirubin thresholds, when to start phototherapy, exchange transfusion, G6PD, and kernicterus prevention.
A yellow baby is one of the most common sights in any postnatal ward. Neonatal jaundice — medically called neonatal hyperbilirubinaemia — affects approximately 60% of term newborns and up to 80% of preterm infants in the first week of life. For most babies, it is a normal and self-limiting part of the transition from womb to world.
But bilirubin — the yellow pigment that causes the colour — is also a neurotoxin. At high enough levels it crosses the blood-brain barrier and damages the basal ganglia, auditory nuclei, and cerebellum, causing a devastating and preventable condition called kernicterus. Every case of kernicterus represents a failure of monitoring or treatment that should never have happened.
The 2022 AAP guidelines fundamentally changed how neonatal jaundice is managed — lowering treatment thresholds, mandating universal screening, and stratifying risk more precisely. This guide explains everything from the basic biology to the clinical decision-making framework.
The yellow colour comes from bilirubin — a breakdown product of haemoglobin. When red blood cells die, haemoglobin is broken down into haem, which is converted to bilirubin. In adults, the liver rapidly conjugates and excretes bilirubin into bile. In newborns, this system is temporarily overwhelmed for several reasons:
The result is a transient rise in unconjugated (indirect) bilirubin in the blood — unconjugated bilirubin is fat-soluble, crosses the blood-brain barrier, and is the form responsible for neurotoxicity.
⚠️ Any jaundice appearing within the first 24 hours is pathological until proven otherwise. The most common cause is isoimmune haemolytic disease (ABO or Rh incompatibility). This is a neonatal emergency — do not wait to observe.
| Cause | Mechanism | Key Clue |
|---|---|---|
| ABO incompatibility | Maternal anti-A or anti-B antibodies attack baby's red cells | Most common haemolytic cause. Mother O, baby A or B. Positive DAT. |
| Rh incompatibility | Maternal anti-D attacks Rh-positive baby's red cells | Rh-negative mother, Rh-positive baby. Prevented by anti-D prophylaxis. |
| G6PD deficiency | Oxidative stress → haemolysis | X-linked. Very common in Indian, African, Mediterranean populations. Can cause severe acute haemolysis. |
| Sepsis | Haemolysis + impaired hepatic conjugation | Unwell baby, temperature instability, raised CRP. |
| Hypothyroidism | Reduced hepatic UGT1A1 activity | Prolonged jaundice + poor feeding + constipation + hypotonia. Check TSH. |
| Breast milk jaundice | Beta-glucuronidase in breast milk increases enterohepatic recirculation | Healthy baby, well feeding, prolonged mild jaundice. Resolves spontaneously. |
| Biliary atresia | Conjugated (direct) hyperbilirubinaemia — bile duct obliteration | Pale/white stools, dark urine, progressive jaundice. Surgical emergency. Check direct bilirubin. |
Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common enzyme defect in the world, affecting approximately 7–10% of Indian males (X-linked condition). In neonates, G6PD deficiency can cause severe and rapidly rising jaundice — particularly when the baby is exposed to oxidative triggers: naphthalene (mothballs), certain medications (nitrofurantoin, dapsone, primaquine), henna, or infection.
The 2022 AAP guidelines recommend G6PD testing for all newborns in high-prevalence populations — which includes India. G6PD-deficient babies are classified as having a neurotoxicity risk factor, which lowers their phototherapy threshold.
The 2022 AAP guidelines made landmark changes compared to the 2004 guidelines — most importantly, lowering phototherapy thresholds especially for late preterm infants (35–37 weeks) and any baby with neurotoxicity risk factors.
| Age (Hours) | ≥ 38 Wk, Low Risk (mg/dL) | 35–37 Wk or ANY Risk Factor (mg/dL) |
|---|---|---|
| 24 hours | 8.0 | 6.0 |
| 48 hours | 13.0 | 11.0 |
| 72 hours | 16.0 | 13.0 |
| 96 hours | 18.0 | 15.0 |
| ≥ 5 days | 18.0 | 15.0 |
Neurotoxicity risk factors that lower the threshold to the right-hand column:
⚠️ Exchange transfusion threshold is approximately 2 mg/dL above the phototherapy threshold at each time point. Exchange transfusion is a high-risk procedure but may be life-saving in severe hyperbilirubinaemia. Any baby approaching exchange threshold requires immediate escalation to a neonatal unit.
👶 Use the RxMedCalc Neonatal Jaundice Calculator — enter gestational age, age in hours, TSB, and neurotoxicity risk factors to get phototherapy and exchange transfusion thresholds per AAP 2022.
Phototherapy works by converting unconjugated bilirubin in the skin into water-soluble isomers (primarily lumirubin) that can be excreted in bile and urine without hepatic conjugation. Blue-green light (wavelength 460–490 nm) is most effective.
Kernicterus is bilirubin-induced permanent neurological damage. It occurs when extremely high unconjugated bilirubin levels saturate albumin binding capacity and free bilirubin crosses the blood-brain barrier. It causes:
Kernicterus is entirely preventable with universal screening, timely phototherapy, and early recognition of risk factors. In India, it remains more common than in high-income countries due to late presentation, delayed initiation of phototherapy, and under-recognition of G6PD deficiency.
After early hospital discharge (which is increasingly common), parents must know the warning signs:
This article is for educational purposes based on AAP 2022 and IAP guidelines. Phototherapy and exchange transfusion decisions must be made by qualified neonatal medical personnel using the full clinical nomogram and individual patient assessment.
Built by an MBBS, AFIH Certified Physician in Punjab, India | RxMedCalc.com