Predicting Significant Hyperbilirubinemia in ABO Incompatibility: Is Cord Direct Antiglobulin Test Useful?

To study the prevalence of direct antiglobulin test (DAT) positivity and outcomes in babies with ABO incompatibility and the role of DAT in predicting need for phototherapy. This was an analytical retrospective cohort study conducted in a tertiary care hospital in South India. DAT was performed routinely in cord blood of all neonates born to O positive mothers. The case records of neonates ≥ 35 weeks of gestation and birth weight > 2000 gm with ABO setting born between January 2019 and December 2020 were reviewed and outcomes were analyzed. Among 2484 live births, there were 426 eligible ABO incompatible births and DAT was positive in 68(15.9%). DAT positive neonates had significantly higher peak mean bilirubin [16.02 mg/dL vs. 13.68 mg/dL, p = 0.00], need for phototherapy in first 24 h [23(33.8%) vs. 32(8.9%), p = 0.00], need for exchange transfusion [2(2.9%) vs. 0(0%), p = 0.025] and immunoglobulin [6(8.8%) vs. 0(0%), p = 0.00]. Cord DAT showed 29.9% sensitivity, 96.9% specificity, 89.7% positive predictive value and 60.1% negative predictive value for predicting need for phototherapy. DAT positivity occurs in a significant proportion of ABO incompatible births and a "selective" cord blood DAT in neonates born to O positive mothers can identify those neonates at risk of significant hyperbilirubinemia with high diagnostic accuracy.