Bilirubin as a Predictor of Neonatal Jaundice

For infants of mothers with blood group O, arterial umbilical cord bilirubin (aUCB) predicts development of neonatal jaundice due to haemolytic disease, according to a study published Sept. 20 in BMC Pediatrics.

"Estimation of UCB at delivery is practicable, cheap and non-invasive," write the authors led by Kelsey D. J. Jones, from Imperial College in the United Kingdom. "It could be easily integrated with the current trend towards routine umbilical cord blood biochemical evaluation practiced in many centers."

Hyperbilirubinaemia is among the most common causes of neonatal admission to hospital, but early identification of infants at highest risk enables targeted primary preventative therapy.

The U.K.-based researchers retrospectively reviewed hospital biochemistry records to identify term deliveries with recorded aUCB (February to November 2010), as well as infant medical records to identify those who developed neonatal hyperbilirubinaemia requiring treatment. It was standard procedure at the hospital to perform umbilical cord gas analysis on all obstetric- led deliveries, and that the GEM4000 blood analyzer automatically provides total bilirubin estimation.

Clinically significant jaundice developed in 2.7 percent of infants with recorded aUCB. Eight cases had a positive direct antiglobulin test (DAT), mostly due to ABO blood type incompatibility. aUCB strongly predicted the development of DAT + ve jaundice, as well as to a lesser extent all-cause jaundice. However, this effect on all-cause jaundice was "critically dependent" on maternal O blood group. Using a cutoff of 35 μmol/l for mothers with blood group O + ve/O-ve increased the pretest probability for all-cause jaundice from 4 percent to 30 percent post-test.

The authors caution about defining cutoff values, noting that the "ideal" cutoff will probably differ between the populations served by different centers.

"Consideration of umbilical cord bilirubin as an index of risk for neonatal jaundice is not a new idea," writes Jones and colleagues. " Substantial differences in reported sensitivity and specificity values may simply have reflected the use of different arbitrary cutoffs…. Our data suggest that venous and arterial values are strongly correlated, but that venous levels are consistently lower than arterial, leaving open the possibility of systematic error when comparing between study groups."

Takeaway: Estimation of aUCB should be considered as a strategy for early identification of infants at risk of neonatal haemolytic jaundice.