Comparison of the direct antiglobulin test and the eluate technique for diagnosing haemolytic disease of the newborn

OBJECTIVE The direct antiglobulin test (DAT) is an important tool for identification of haemolytic disease of the newborn (HDN) caused by erythrocyte immunization. Although this test has been used for decades, accurate insights into its diagnostic properties and optimal use in the diagnosis of HDN are limited. We aimed to gain more insight into the diagnostic properties of the DAT for HDN by comparing it with erythrocyte eluate screening. DESIGN AND METHODS DAT and erythrocyte eluate screening was performed in umbilical cord blood of neonates obtained from 317 consecutive deliveries. Clinical jaundice was scored 4-6 days after delivery for the determination of HDN. RESULTS In 21 neonates a positive DAT and in 61 neonates a positive eluate screening was found, while only 4 cases of HDN were observed. For the overall population the positive predictive value (PPV) and specificity of the DAT for HDN were 10% and 93% respectively and in the population of neonates with abnormal post-partum jaundice population the PPV and specificity were both 100%. The DAT missed two cases of HDN. These missed cases were, however, positive in the erythrocyte eluate screening. CONCLUSION The detection of clinically irrelevant ABO immunization limits the specificity of the DAT and eluate for HDN in ABO-incompatible pregnancies. For optimal use, the DAT should be requested only in cases of jaundice and be interpreted in the context of ABO-incompatibility. Finally, a negative DAT does not rule out HDN. When clinical suspicion is high, an eluate should be added following a negative DAT.