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Lack of clinical significance of “enzyme‐only” red cell alloantibodies

In a retrospective study on samples from 10,000 recently transfused patients, 35 samples were found to contain an antibody that reacted with ficin‐treated red cells but was not demonstrable by low‐ionic‐ strength saline solution and indirect antiglobulin test (LISS‐IAT). In those 35 patients, the specificity of the antibody was such that each patient would have been transfused with antigen‐negative blood had the antibody reacted in LISS‐IAT. Tests on red cells from the units already transfused showed that 19 patients had among them received, by chance, 32 antigen‐positive and 74 antigen‐negative units. The remaining 16 patients had among them received 57 units that were, again by chance, all antigen negative. One patient given antigen‐positive blood suffered a delayed transfusion reaction; in two others the antibodies became LISS‐IAT active after transfusion. However, similar changes to the LISS‐ IAT‐active state were seen with two antibodies of patients given only antigen‐negative blood. Also found in the 10,000 patients were 28 clinically insignificant antibodies, 77 sera in which the antibody was too weak to identify, and 216 autoantibodies that reacted only with ficin‐treated red cells. These data support a belief, generally held in the United States but not necessarily elsewhere, that the use of protease‐treated red cells for routine pretransfusion tests creates far more work than the accrued benefits justify.