Abstract
Introduction: The direct antiglobulin test (DAT) detects the presence of IgG and/or C3 on the red blood cell (RBC) membrane and is used to diagnose autoimmune hemolytic anemias as well as hemolytic disease of the fetus and newborn (HDFN). A positive DAT in a neonate occurs when maternal IgG crosses the placenta and binds to fetal RBCs, which may lead to hemolysis and clinical manifestations of HDFN such as hyperbilirubinemia. Historically, DATs in umbilical cord blood samples were performed manually. We have recently switched to using the Ortho Vision Analyzer (gel technology) for this purpose in our institution, and noticed a trend toward stronger positive reactions. The purpose of this study was to compare the DAT results obtained with the conventional tube method and the gel method, and their association with hyperbilirubinemia and/or the need for phototherapy in the neonates tested.
Methods: We retrospectively reviewed all cord DAT results of infants born between January 2016 and June 2018. We included all tests of neonates of blood group A or B born to blood group O mothers who had a positive DAT and performed a retrospective chart review to collect the following data: DAT strength, gestational age, birth weight, hematocrit, blood type, initial and peak serum total bilirubin levels, use of phototherapy, antibody screening results, and transfusion history. Neonates whose mothers had a positive antibody screen were excluded from the analysis.
Results: During the study-period, 100 ABO-incompatible neonates with a positive DAT were tested by the tube and gel methods (50 with each methodology) and met our inclusion criteria. Their demographic information and laboratory results, including the strength of the positive DAT are in Table 1. There was a clear trend toward stronger DAT results since the gel methodology was introduced; the most common result in the Ortho Vision Analyzer was 1+ positive (52%), and 40% of neonates had a 2+ positive result. The latter was only seen in 2% with the tube method. Furthermore, although there were no significant differences in any demographic or laboratory parameters between the two groups of neonates, an increased percentage of those tested with the new methodology (23/50 or 46%) received phototherapy compared with 14/50 (28%) of those tested manually (Figure 1).
Conclusions: We found that the Ortho Vision Analyzer produced stronger DAT results compared to the tube method without evidence of increased hemolysis. It is essential that Transfusion Medicine physicians communicate the change in methodology to neonatologists to make them aware of the reason for the stronger DAT results in order to avoid unnecessary phototherapy.
No relevant conflicts of interest to declare.
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