Management of transfusion needs in a case of immunizing anti-M antibody in a patient with acute myeloid leukemia.

Anti-M is a relatively common "naturally occurring" antibody. Unexpected alloantibodies in patient's serum other than ABO isoagglutinins (e.g., anti-M) may cause a discrepancy in the reverse grouping. As long as anti-M does not react at 37°C, it is clinically insignificant for transfusion. However, we found this antibody to be of "immunizing" type which was reactive at 37°C and AHG phase and showing problems in blood grouping and crossmatch. This antibody had both IgM and IgG components. When "M" antibodies active at 37°C are encountered, antigen-negative or red cells that are compatible with an indirect antiglobulin test should be provided.