Alloimmunization in patients with warm autoantibodies. A retrospective study employing three donor alloabsorptions to aid in antibody detection.

We examined the value of performing alloabsorptions to detect clinically significant alloantibodies in patients with warm autoantibodies who must receive crossmatch-incompatible blood. One hundred and twenty-five (125) patients were evaluated using alloabsorption with red cells (RBCs) from three donors: R1R1, R2R2, and rr, whose phenotypes other than Rh were selected to exclude 98 percent of clinically significant alloantibodies. This technic was selected rather than autoabsorption due to insufficient quantities of patient cells available and to the possible presence of transfused cells in some instances. Patients were divided into three risk categories: I--no prior pregnancy or transfusion; II--history of pregnancy and/or one to five transfusions; and III--greater than five transfusions. No significant alloantibodies were found in 32 category I patients. Of 74 category II patients, 13 (17.5%) had significant alloantibodies detectable after absorption. Six of 19 (31.5%) category III patients had alloantibodies. The majority showed Rh specificity: anti-E (13), -C (6), -c (2), -D (1). Anti-K was found in five samples. Forty-two (42%) percent of the alloantibodies were undetectable prior to the alloabsorptions. We conclude that category II and particularly category III patients are at significant risk of allosensitization and should be evaluated by an absorption procedure prior to the transfusion of crossmatch-incompatible red cells.