Use of the erythrocyte rosette test to screen for excessive fetomaternal hemorrhage in Rh-negative women.

The possibility of Rh immune globulin failure exists when a fetomaternal hemorrhage exceeds 25 to 30 ml of whole blood and only one 300 micrograms vial of Rh immune globulin is administered. In this prospective study of 1000 consecutive Rh-negative women who were delivered of Rh-positive newborn infants, the presence of fetal erythrocytes in maternal blood was identified with use of both the Du test read microscopically and the erythrocyte rosette test. All positive tests prompted fetomaternal hemorrhage quantification with use of a modified Kleihauer-Betke acid elution test. Nineteen patients demonstrated a positive rosette test, and the only positive Du tests were in five of these 19. Six of the nineteen had levels of greater than 30 ml of whole blood for an incidence of 0.6% for fetomaternal hemorrhage exceeding the protective capabilities of the standard Rh immune globulin dosage. In experiments with simulated fetomaternal hemorrhage, all 79 samples, containing from 2.5 to 70 ml of fetal whole blood, were positive according to the erythrocyte rosette test. Applying the Du test to the same samples resulted in a 30% false negative rate at the level of a 30 ml simulated hemorrhage. Based on sufficient sensitivity, ease of interpretation, and reasonable cost, the rosette test appears to be a superior screening test for excessive fetomaternal hemorrhage in Rh immune globulin candidates.