Anti-M antibodies: Biphasic (reactive at room temperature and at 37°C): A case series.

Anti-M antibody, which is not reactive at 37°C, is not clinically significant. Reports of clinically significant anti-M antibodies causing hemolytic disease of the fetus and the newborn (HDFN) and delayed hemolytic transfusion reaction (DHTR) are available. We report 13 cases of anti-M antibodies reactive at room temperature (RT) and at 37°C. These were found in patients of varied age groups (11 months to 85 years) with varied clinical diagnosis. All the female patients were multigravida. In all cases, antibody screening was positive at RT as well as at the indirect antiglobulin test (IAT) phase. Providing "M"-antigen negative transfusions is the best therapy in this situation. Provision of red blood cell (RBC) antigen phenotyped donor registry shall ensure quick provision of antigen-negative blood for transfusion in emergency situations.