A retrospective study of positive antibody screens at delivery in Rh-negative parturients

Purpose: Rhesus- (Rh-) negative women receiving anti-D antibodies antenatally often have a positive antibody screen at delivery. We investigated the incidence of positive antibody screens at delivery in this population and examined how the presence of positive antibody screens affected the time required to obtain type and screen or type and crossmatch results. Methods: Records of parturients who had type and screen or type and crossmatch done upon presentation for delivery from June to October 2007 were examined to determine estimated gestational age at admission, Rh-status, the presence of positive antibody screens, and the time interval from receipt of specimen in the blood bank to the availability of antibody screen results. Results: Of the 480 specimens sent for type and screen or type and crossmatch, 20% of parturients were Rh-negative, with 57% of those demonstrating a positive antibody screen compared with 4% of the Rh-positive parturients (P < 0.01). In the Rh-negative group, 100% (95% CI 98- 102) of positive antibody screens were anti-D antibodies. There was a longer median laboratory time for Rh-negative vs Rh-positive parturients (146 vs 65 min), for antibody positive vs antibody negative parturients (243 vs 65 min) (P < 0.001 for both), but not for Rh-positive/antibody positive vs Rh-negative/antibody positive patients (312 vs 218 min) (P = 0.09). The antibody screen was positive in 100% of Rh-negative parturients until 37 weeks gestation, after which there was a decline. Conclusions: Rh-negative parturients who receive anti-D antibodies antenatally have a higher incidence of positive antibody screens at delivery than Rh-positive parturients due to the presence of anti-D antibodies.