Jaundice is clinically detectable in the newborn when the serum bilirubin levels are greater than 85 micromols per litre. This occurs in approximately 60% of term infants and 80% of preterm infants. Hyperbilirubinaemia is either unconjugated (which is potentially toxic but may be physiological or pathological) or conjugated (not toxic; always pathological). Without treatment, high levels of unconjugated bilirubin may lead to kernicterus.