Comparative Clinical Outcome Based on Direct Antiglobulin Test Status in Neonates with ABO Incompatibility: A Prospective Cohort Study

Introduction: ABO Haemolytic Disease of the Newborn (ABOHDN) is a significant but often under-recognised cause of neonatal haemolysis. A positive Direct Antiglobulin Test (DAT) is observed in 20-40% of ABO incompatible cases. Aim: To compare clinical outcomes between DAT-positive and DAT-negative neonates and evaluate the predictive value of DAT in ABO incompatible newborns. Materials and Methods: This prospective cohort study was conducted at Chettinad Hospital and Research Institute, Kelambakkam, Chennai, Tamil Nadu, Southern India, from February 2024 to March 2025. A total of 288 neonates born to mothers with blood group O who underwent cord blood DAT testing were included. Based on DAT results, neonates were categorized as DAT-positive or DAT-negative. The primary outcome was the need for phototherapy. Secondary outcomes included the timing of hyperbilirubinemia, peak bilirubin levels, duration of phototherapy, haemoglobin levels, and readmission rates. Data were statistically analysed using Student’s t-test or the Wilcoxon rank-sum test for continuous variables and the Chi-square or Fisher’s exact test for categorical variables. Results: Among 288 neonates, 60 (20.8%) were DAT-positive and 228 (79.2%) were DAT-negative. Phototherapy was needed in 62% of DAT-positive neonates versus 28% in DAT-negative (RR: 2.98, 95% CI: 1.88-4.72; p<0.001). DAT-positive neonates required phototherapy earlier, by a mean of 28.7 hours (p<0.001). No significant differences were noted in peak bilirubin, phototherapy duration, or haemoglobin levels. Readmission for phototherapy was higher in DAT-positive neonates (RR: 2.34; p=0.047). DAT positivity and gestational age independently predicted phototherapy need. DAT showed moderate specificity of 0.88 (95% CI: 0.83-0.92) but low sensitivity of 0.37 (95% CI: 0.27–0.45), with an AUC of 0.621 (95% CI: 0.569-0.674). Conclusion: Cord blood DAT performed in neonates born to O-positive mothers can independently predict the need for phototherapy. However, its limited sensitivity restricts its utility as a sole screening tool in ABOHDN.