[Neonatal blood group incompatibility due to anti-M antibodies].

Neonatal blood group antagonism due to anti-M antibodies is extremely rare. The case is reported of a neonate with moderately severe haemolytic anaemia due to anti-M which required two blood transfusions. Although anti-M antibodies are as a rule regarded as clinically irrelevant, and although they react almost exclusively at lower temperatures, they may in exceptional cases be demonstrated at 37 degrees C, as in the patient described; they may then cause haemolysis. Most strikingly, the direct Coombs test in this patient was negative; this phenomenon has been described before. In unexplained haemolytic anaemia of a newborn, even in the presence of a negative direct Coombs test, the possibility of blood group antagonism should be considered.