[A case of neonatal ABO immunization which was difficult to diagnose. The mother with blood group A2 and the infant with negative direct antiglobulin test].

In caucasians, in about 15 percent of all pregnancies the mother has blood group O and the child blood group A or B which is the usual setting in cases of HDN due to ABO-incompatibility. We describe a case of HDN where the mother had blood group A2 and no irregular erythrocyte antibodies. The patient, who was born at full term, had blood group A2B and negative DAT (Direct Antiglobulin Test). At 36 hours of age exchange transfusion was performed due to a serum bilirubin level of 340 (< 150) mumol/l. The mother had high titres of anti-B antibodies of IgG type and elution indicated presence of anti-B antibodies on the child's erythrocytes.