Jaundice in the first 24 hours: ABO incompatibility

Jaundice that appears within the first 24 hours of life is never physiological. Physiological jaundice starts on day 2 or 3, peaks around day 4 to 5 and settles by 2 weeks. Jaundice at 18 hours means haemolysis until proven otherwise, and the raised reticulocyte count and spherocytes on the film confirm that red cells are being destroyed.

The most likely cause is ABO haemolytic disease of the newborn. This occurs when a group O mother, who naturally makes IgG anti-A and anti-B, delivers a group A or B baby. The maternal IgG crosses the placenta and coats the baby's red cells, which are then removed by the spleen, producing spherocytes. Unlike RhD disease, it can affect a first pregnancy and is usually milder.

The test that confirms immune haemolysis is the direct antiglobulin test (DAT, or Coombs test) on the baby's blood. It detects antibody bound to the surface of the baby's red cells. A positive DAT with the right blood group combination makes the diagnosis. In ABO disease the DAT can be only weakly positive, so a negative result with strong clinical suspicion still warrants treatment as haemolysis.

Management is guided by the bilirubin level plotted on an age-in-hours chart, as in the Queensland Clinical Guideline on neonatal jaundice. At 185 micromol/L at 18 hours this baby is likely to need phototherapy, with repeat bilirubin in 4 to 6 hours, and exchange transfusion or intravenous immunoglobulin if the level rises rapidly despite treatment.

Hereditary spherocytosis also causes spherocytes and early jaundice; it is considered if the DAT is negative, along with G6PD deficiency in babies of Mediterranean, African or Asian background.