(P-PH-5) Why Do People Still Make Anti-D Over 50 Years after the Introduction of Rho(D) Immune Globulin? A BEST Collaborative Study Presented on Behalf of the RADAR Study Investigators.

Background/Case Studies: Rho(D) immune globulin (RhIg) prophylaxis is used in pregnancy to reduce RhD alloimmunization risk. Despite widespread RhIg availability in high and high-middle income countries, RhD alloimmunization persists. We investigated potential sources of RhD alloimmunization in the post-RhIg era. Given RhIg prophylaxis in pregnancy is now standard of care, we hypothesized transfusion might be the most frequent source as RhPos blood transfusion to RhNeg or unknown blood type individuals may occur with inventory constraints or massive transfusion.

Study

Design/Methods: In this international retrospective descriptive study, medical records were reviewed for potential sources of new anti-D identified during 2018-2022 in patients born from 1965-2005. Transfusion, pregnancy, intravenous drug use (IVDU), or transplantation were potential sources.

Results/Findings: There were 1072 study patients identified at 28 centers in 5 countries (US, CA, UK, NZ, BR). Results are summarized in Table 1. Most patients (743, 69%) had a single potential source, most commonly pregnancy among females and transfusion among males. When all potential sources were included, males were more likely than females to have transfusion history (225 [67%] vs. 137 [19%], p< 0.0001) and to have confirmed or suspected IVDU (100 [30%] vs. 138 [19%], p< 0.0001). Among females with pregnancy history, 113 (18%) had evidence of lack of healthcare access, 103 (17%) had pregnancy in another country, and 17 (3%) refused RhIg. Among transfused patients, males were more likely to have received RhPos RBCs or whole blood (136 [60%] vs. 28 [20%], p< 0.0001) and/or RhPos apheresis platelets (77 [34%] vs. 17 [12%], p< 0.0001) at the hospital that identified the anti-D.


Conclusions: Pregnancy remains the most frequent potential source of RhD alloimmunization, in spite of widespread RhIg availability. Transfusion is the most frequent in males, possibly reflecting blood allocation practices designed to protect women of childbearing potential. The unexpected magnitude of IVDU among patients with RhD alloimmunization has not been reported in the literature to date and merits further study.