Two cases of "hrB-like" autoantibodies appearing as alloantibodies

Two cases are described in which autoantibodies mimicked alloantibodies. The direct antiglobulin test (DAT) on the red cells (RBCs) from both patients was negative when routine manual hexadimethrine bromide (Polybrene) and enzyme-linked antiglobulin techniques were used. The RBCs also did not react on direct bromelin and direct Polybrene tests. However, an "hrB-like" antibody was eluted from the RBCs of both patients. The sera from these patients reacted with all e+ hrB+ RBCs but not with e+ hrB-, e-, or their own RBCs. The antibody in the serum of one patient was not adsorbed by R2R2 RBCs. Serologic tests initially suggested (by direct testing and adsorption studies) that the serum antibodies were alloantibodies rather than autoantibodies. RBCs taken from one patient, 8 months after her sample was first referred to our laboratory, reacted with a serum sample from her first admission. An RBC sample taken from the other patient, initially typed e+ and hrB- but 1 month later typed e+ and hrB+ by using the same anti-hrB sera, was used to test the earlier samples.