Introduction and causes
Clinically detectable jaundice (serum bilirubin > 80micromol/L) is common (present in 100% of preterm babies, 60% of term babies). It is the main reason for delayed discharge of babies from the postnatal ward. It is usually benign but has a devastating effect at toxic levels and as such needs to be managed safely as well as efficiently.
Jaundice can be classified into two categories:-
- Unconjugated hyperbilirubinaemia, which is the most usual form encountered in the newborn and presents in the first week.
- Conjugated hyperbilirubinaemia, which is less common, presents later (usually 2-4 weeks) and is most commonly due to hepatitis of various kinds but a surgical cause needs to be ruled out.
Potential Dangers of Hyperbilirubinaemia
a) Unconjugated hyperbilirubinaemia:-
Until bilirubin can be conjugated by UDP - glucuronyl transferase it cannot be excreted. Bilirubin is bound to albumin on a mole to mole basis. When the total unconjugated bilirubin exceeds the ability of albumin to bind it the excess crosses the blood brain barrier in greater amounts and can cause kernicterus.
Kernicterus is the term used for unconjugated bilirubin encephalopathy. Three clinical phases have been identified: hypotonia, lethargy, poor suck in the first day or so, hypertonia +/- opisthotonus towards the end of the first week when there is often also a high-pitched cry , fever and seizures and then a third phase when the baby again becomes hypotonic. The recent British paediatric surveillance of cases of kernicterus reported a 25% risk of death between 2003 and 2005. Survivors tend to have choreoathetoid cerebral palsy and hearing impairment.
b) Conjugated hyperbilirubinaemia is not usually harmful in itself but may reflect significant underlying disease and requires investigation.
Causes of Unconjugated Hyperbilirubinaemia
Physiological jaundice is due to delayed maturation of conjugation; bilirubin production exceeds excretion. Normally bilirubin levels peak at 3-4 days in healthy bottle fed full term infants, towards the end of the first week in breast fed babies and 7-10 days in preterm infants (depending on gestational age).
Certain conditions, referred to in the algorithms as "risk factors", may enhance an existing physiological jaundice by either increasing the hepatic bilirubin load, temporarily inhibiting the conjugating enzyme or causing general liver dysfunction. This may result in levels of unconjugated bilirubin sufficiently high as to cause kernicterus.
These include:-
- Any haemolytic condition such as Rh incompatibility, ABO incompatibility, glucose-6-phosphate dehydrogenase deficiency, pyruvate kinase deficiency, congenital spherocytosis, septicaemia and occasionally acute pyelonephritis.
- Increased red cell mass due to delayed clamping of the cord (PCV >0.65), twin to twin transfusion (monozygotes) and occasionally in the child of a diabetic mother.
- Lysis of enclosed haemorrhage such as cephalohaematoma, intraventricular haemorrhage, extensive bruising from breech delivery and around a fracture site (usually humerus or clavicle).
- Breast fed infants who have an inadequate milk intake and may also be dehydrated
- Conditions which cause marked hepatic dysfunction such as galactosaemia and fructosaemia.
- Extremely rare conditions (eg Crigler-Najjar) where the conjugation enzyme is absent or defective.
- Some drugs such as sulphonamides, salicylates and chloramphenicol may displace bilirubin from albumin binding sites, causing kernicterus at lower than usual total unconjugated bilirubin levels. These drugs are not normally used in the newborn.
There is often a history of jaundice in a previous sibling.
Investigations
Visual assessment of jaundice is not reliable, especially in our ethnically diverse population. Well babies of over 36 weeks gestation (and >2000g) presenting with jaundice when they are >24 hours old will probably only need a transcutaneous screen. Others will need further investigations.