RESUMO
Anti-M antibodies are usually assumed to be naturally occurring and to consist of immunoglobulin M reacting at 4degrees C. They are not usually considered to be clinically significant, however, many of them have an immunoglobulin G component reacting at 37degrees C and can be correlated with hemolytic disease of the newborn (HDN). We report a moderate case of HDN by anti-M. A 2-days old baby born from a mother with preeclampsia as a second pregnancy was admitted due to anemia, hyperbilirubinemia and hypoxic encephalopathy. The blood type of mother was AB, ccDEE, NN, and the blood type of baby was A, D+, and MN. Antibody screening and identification identified anti-M antibody which was strong reactive at 37degrees C albumin and antiglobulin phase in both baby's and her mother's serum. The direct antiglobulin test of baby's red blood cells was negative. The infant was transfused with group O red cells which have negative to trace reaction with her mother's serum in antiglobulin phase. Two days later, the hemoglobin level elevated from 6.7 g/dL to 15.9 g/dL falled to below 11 g/dL quite soon. After all, newborn died of cardiac arrest due to her basic disease at age of 49 days; metabolic acidosis and hypernatremia.