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.