IgM Warm Autoantibodies Causing Autoimmune Hemolytic Anemia in a Pediatric Patient.

Most often, IgM-mediated autoimmune hemolytic anemia (AIHA) presents as cold agglutinin disease in the pediatric population. The IgM warm agglutinins are rare, with few reports in the literature. This case study describes a 5 year old girl with nausea, abdominal pain and jaundice, and a hemoglobin of 5.5 g/dL who was diagnosed with a warm reactive IgM AIHA. The laboratory workup revealed a pan-reactive antibody and a direct antiglobulin test negative for IgG and C3. A thermal amplitude assay revealed reactive IgM antibodies at 37°C, 30°C, 25°C, and 4°C and an antibody titer of 1:8. An adsorption for IgM-specific autoantibodies exposed underlying anti-E and anti-Cw alloantibodies. Transfusion of phenotypically matched red blood cell units supported ongoing hemolysis. The AIHA treatment included steroids followed by rituximab with complete resolution. A literature review shows variable outcomes for warm AIHA in the pediatric population and often describes the presence of warm reactive IgM-mediated AIHA as an indicator for poor prognosis.