Low frequency of anti-D alloimmunization following D+ platelet transfusion: the Anti-D Alloimmunization after D-incompatible Platelet Transfusions (ADAPT) study.

The reported frequency of D alloimmunization in D- recipients after transfusion of D+ platelets varies. This study was designed to determine the frequency of D alloimmunization, previously reported to be an average of 5 ± 2%. A primary anti-D immune response was defined as the detection of anti-D ≥ 28 d following the first D+ platelet transfusion. Data were collected on 485 D- recipients of D+ platelets in 11 centres between 2010 and 2012. Their median age was 60 (range 2-100) years. Diagnoses included: haematological (203/485, 42%), oncological (64/485, 13%) and other diseases (218/485, 45%). Only 7/485 (1·44%; 95% CI 0·58-2·97%) recipients had a primary anti-D response after a median serological follow-up of 77 d (range: 28-2111). There were no statistically significant differences between the primary anti-D formers and the other patients, in terms of gender, age, receipt of immunosuppressive therapy, proportion of patients with haematological/oncological diseases, transfusion of whole blood-derived or apheresis platelets or both, and total number of transfused platelet products. This is the largest study with the longest follow-up of D alloimmunization following D+ platelet transfusion. The low frequency of D alloimmunization should be considered when deciding whether to administer Rh Immune Globulin to D- males and D- females without childbearing potential after transfusion of D+ platelets.