Haemolytic disease of the newborn (HDN) is caused by maternal immunoglobulin (Ig) G acting against antigens expressed on mature fetal red cells. Anti-M antibodies active at 37°C are a rare cause of HDN.¹ We report data, arising from the investigation of a neonate with severe transient pure red-cell aplasia, indicating that anti-M can cause hypoplastic HDN by inhibition of erythroid precursor growth, as frequently occurs with anti-Kell antibodies.²

A female neonate presented at 4 weeks of age with severe hypoplastic anaemia (haemoglobin 3.7 g/dl, reticulocytes …