A combined flow cytometry-based method for fetomaternal hemorrhage and maternal D

BACKGROUND: The fetomaternal bleed assay by flow cytometry is a semiquantitative test used to determine the volume of fetomaternal hemorrhage (FMH). We have enhanced this method by combining the fetomaternal bleed assay with a D antibody in the same tube to determine the maternal D as well as the need for Rh immune globulin (RhIG) administration. STUDY DESIGN AND METHODS: The performance of the FMB/D assay was compared against the Kleihauer-Betke (KB) acid elution method for the quantitation of fetal bleed and tube method for the maternal D determination. Peripheral blood cells from the pregnant women were fixed and permeabilized, incubated with monoclonal antibodies directed against fetal hemoglobin (Hb F) and D, and analyzed by flow cytometry. The relative concentration of Hb F-containing cells to adult cells was used to determine the volume of the FMH. In addition, the cells were identified as D+ or D-. RESULTS: D typing of nonpregnant adult donors matched in all cases with the tube method with a mean value of 0.01% Hb F-positive cells (n = 25). D typing of pregnant or postpartum samples matched in all cases (n = 100), and the RhIG dose calculated by the percentage of Hb F for each method matched 97 percent (n = 36; p = 0.324). The one discrepant sample was consistent with the acknowledged overestimation when using the KB method. CONCLUSION: The highly precise anti-Hb F flow cytometric method was combined with maternal D determination by anti-D. This method correlates well with standard assays eliminating the need for additional testing without sacrificing clinical information.