Hour-specific bilirubin nomogram in infants with ABO incompatibility and direct Coombs-positive results.

OBJECTIVE: To determine the usefulness of the hour-specific Bhutani et al bilirubin nomogram when applied to infants with Coombs-positive test results.

DESIGN: Retrospective chart review.

SETTING: Term nursery and neonatal intensive care unit of a university-affiliated hospital.

PATIENTS: All infants with A+ or B+ blood type born in our center from September 1, 2006, through August 31, 2008, to mothers with O+ blood.

OUTCOMES: Proportion of infants with Coombs-positive results from the nomogram zones who required phototherapy and comparison of the percentage of infants with Coombs-positive results in each zone with the percentage of those with Coombs-negative results in each zone.

RESULTS: A total of 240 infants with Coombs-positive and 460 with Coombs-negative results having a gestational age of 35 weeks or older were evaluated. Sensitivity and specificity of data for infants with direct Coombs-positive results in zone 4 (high risk; 74.2% and 97.1%) and those for infants in zones 3 (high-intermediate risk) and 4 combined (96.7% and 83.7%) compared favorably with the data from the Bhutani et al cohort, which had direct Coombs-negative results (54.0% and 96.2% for zone 4; 90.5% and 84.7% for zones 3 and 4 combined). The likelihood ratio for infants with direct Coombs-positive results in zone 4, 25.8 (95% confidence interval, 11.4-58.4), was twice that of the Bhutani et al cohort, 14.1 (11.0-18.1). The nomogram performed well in directing the timing of bilirubin level follow-up. All infants in zones 3 and 4 with Coombs-positive results were followed up after hospital discharge. None required an exchange transfusion or developed bilirubin encephalopathy.

CONCLUSIONS: The Bhutani et al bilirubin nomogram reliably identified infants at gestational age of older than 35 weeks with direct Coombs-positive results who were at risk for significant hyperbilirubinemia and directed the timing of follow-up for these infants. This finding has direct clinical applicability to the health care professional practicing in the newborn nursery.