757 - Clinical Utility of Direct Antigen Test in Hemolytic Disease of Newborn

Prevention of Rh alloimmunization in pregnant women is imperative to avoid fatal complications of hemolytic disease of the newborn (HDN). The introduction of antenatal and postpartum RhoGAM has measurably decreased the incidence of RhD-HDN. Therefore, recommendations for HDN screening advise using a direct antiglobulin test (DAT) for infant of mothers of blood group O or Rh-negative.

Objective: Since Rh-negative women receive composite RhoGAM for HDN prevention, we assessed cord blood DAT to determine its clinical utility for HDN evaluation in Rh-negative women with a blood type other than O in order to eliminate unnecessary testing in neonates.

Design/Methods:

After IRB approval, we retrospectively evaluated neonates ≥ 35 weeks of gestation admitted to the newborn nursery in July 2019-July 2021 at our institution. The cohort included neonates of non-O, Rh-negative maternal blood groups who received RhoGAM. We correlated the neonate’s DAT status with discharge bilirubin levels, length of stay and calculated the positive predictive value for the need for phototherapy. Continuous variables and frequencies were analyzed using student’s t-test and chi-square tests. Statistical significance was determined using a two-tail p-value < 0.05 with SPSS V24.

Results: 266 neonates met the inclusion criteria. The cohort of neonates consisted of 126 (47.4%) who had blood group A, 65 (24.4%) group B, 16 (6%) group AB, and 59 (22.2%) group O. The DAT was positive in 36 (13.5%) of neonates. Median bilirubin at discharge and length of stay were 6.5 µmol/L and two days, respectively. Two neonates who were DAT-positive required phototherapy, one of them had an increased risk of early onset sepsis. The positive predictive value of DAT was 8.3% in the study. We found no statistically significant difference between DAT+ and DAT- with the need for phototherapy (p=0.03). We also found that increased length of stay was associated with the requirement of phototherapy (p=0.033). 

Conclusion(s):

The probability of developing maternal antibodies associated with HDN after receiving RhoGAM is minor. Our findings were consistent with insignificant positive predictive value of DAT when screeding for HDN in mothers received RhoGAM during the pregnancy. Hence routine DAT is of limited benefit and should be ordered only for ABO incompatibility. Eliminating redundant testing can reduce healthcare costs, time expenditure, and unnecessary heal sticks (Figure 1) Further research is warranted to determine the neonatal outcome.