Use of the gel agglutination technique for determination of fetomaternal hemorrhage

BACKGROUND: Adequate administration of Rh immune globulin requires an accurate determination of the number of D‐positive cells in the circulation of D‐negative women. Although several tests have been described for the detection of fetomaternal hemorrhage, there is still a need for a rapid, simple, and clinically relevant screening test. STUDY DESIGN AND METHODS: Serial dilutions of a monoclonal anti‐D were incubated with stock solutions (0.2 mL) of adult D‐negative red cells in the absence or presence of various amounts of fetal D‐positive cells (0.1, 0.2, 0.3, 0.4, and 0.5%). After incubation, the supernatants were tested against D‐positive red cells by using the new, gel agglutination technique (GAT). After the GAT was adapted to detect D‐positive cells at concentrations of > or = 0.2 percent, unselected postpartum samples from D‐negative women (n = 420) who delivered D‐positive infants were analyzed by both the new test and the Kleihauer‐Betke test (KBT). RESULTS: Three of a total of 420 postpartum samples were positive (> or = 0.4% fetal cells), and 406 were negative in both tests. One had 0.5‐ percent fetal cells in the KBT and gave negative results in the GAT. The latter test was, however, performed after administration of Rh immune globulin. The KBT gave false‐positive results in two cases, because of hereditary persistence of hemoglobin F, and the GAT gave a false‐positive reaction in one case because of a maternal weak D variant. In the remaining seven cases, the KBT results were only weakly positive (0.2%) and could not be attributed solely to D positive red cells. CONCLUSION: The GAT is suited for routine screening. It provides rapid and specific detection of D‐positive red cells at clinically relevant concentrations. The test may (rarely) yield false‐negative results due to insufficient administration of Rh immune globulin before testing.