Elucidation of alloantibodies in autoimmune haemolytic anaemia.

Forty-one patients with autoimmune haemolytic anaemia (AIHA), who had free antibody in their sera, were investigated for the presence of alloimmune erythrocyte antibodies using the ZZAP autoabsorption technique. Patients were subdivided into three risk categories: (I) no prior pregnancy or transfusion; (II) history of pregnancy and/or one to five transfusions; and (III) greater than 5 transfusions. A total of 13 (32%) of the 41 patients exhibited significant alloantibodies. Of 11 category-I patients 2 (18%) had significant alloantibodies. Eight (31%) of the 26 category-II patients had significant alloantibodies and 3 (75%) of the 4 category-III patients had significant alloantibodies after absorption. The majority showed Rh specificity: anti-E(8), -C(3), -Cw(1). Anti-K was found in 6 samples and 1 had anti-Fya. Alloantibodies had not been suspected prior to autoabsorption in 10 (77%) of the 13 patients with alloantibodies. These findings underline the importance of performing autoabsorption in AIHA when free autoantibody is present in the serum. Additionally, Rh phenotyping performed on ZZAP-treated cells showed complete agreement with that ascertained using pure IgM Rh typing sera and untreated cells.