Background: Anti-M is most often assumed to be naturally occurring and can be comprised of a mixture of predominantly immunoglobulin(Ig)M with a lesser IgG component. Anti-M-antibodies usually do not react at 37°C and therefore are considered to be of little clinical significance.
Methods: A 28-year-old man presented with hemorrhagic shock from numerous injuries sustained in a motor vehicle collision. The patient received several units of red blood cells (RBCs). The antibody screen, the direct antiglobulin test (DAT), and the RBC genotype were sent for laboratory evaluation.
Results: A total of 12 days after the first antibody screening result was negative (7 days after transfusion), the lowest hemoglobin value was 5.5 g per dL, and we observed a positive antibody screening result and DAT with immunoglobulin (Ig)G anti-M identified. After transfusion of 4 units of M antigen-negative RBC, the post-transfusion hemoglobin level increased to 8.9 g per dL.
Conclusion: Obtaining M antigen-negative compatible RBCs is necessary in patients demonstrating IgG anti-M in plasma.
Keywords: anti-IgG; anti-IgM; anti-M; delayed hemolytic transfusion reaction; direct antiglobulin test; red blood cell transfusions.
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