Rare case of warm IgM autoimmune hemolytic anemia

Cold agglutinins are IgM-mediated autoimmune hemolytic processes that most often cause destruction of red blood cells at colder temperatures. Here we describe a case of a patient with history of living donor renal transplantation that developed an atypical autoantibody causing profound anemia and hemolysis which, although IgM in nature, reacted best at warmer temperatures and was caused by a lymphoproliferative disorder. The investigations and serological findings here raise awareness to less common forms of autoimmune hemolytic disorders and describe specialized tests that can help uncover these antibodies. This case also highlights a rare presentation of post-transplant lymphoproliferative disorder manifesting clinically as hemolytic anemia.