RESUMEN
Anti-John Milton Hagen (JMH) is a high-titer, low-avidity (HTLA) antibody against the high frequency red blood cell (RBC) antigen JMH. It occurs very rarely and has not yet been reported in Korea. Here, we report a case of anti-JMH antibody identified in a 92-year-old man without previous blood transfusion history, who had been hospitalized with pneumonia. The patient's hemoglobin level was reduced to 7.6 g/dL on the 35th day of hospitalization, requiring RBC transfusion. Antibody identification test revealed antibodies that showed pan-reactivity to all panel cells at the antiglobulin phase. A titration test confirmed that it was a HTLA antibody. He was given one least-incompatible unit of RBC without any adverse events, and his hemoglobin level increased to 9.3 g/dL. The patient's sample was referred to a reference laboratory and the antibody was identified as anti-JMH. He was successfully transfused with 6 additional units of least-incompatible RBCs without complication. HTLA antibodies against high frequency antigens, such as anti-JMH, are less likely to cause significant destruction of transfused antigen positive RBCs. However, identifying the specificity of these antibodies is necessary to appropriately understanding the clinical significance of the antibody, detecting other clinically important alloantibodies that may coexist, and determining the appropriate blood for transfusion.