No abstract

The molecular characterization of the subgroup A3 remains unclear. Four unrelated A3 blood donors were studied. Family studies were possible in three of them. The A3 subgroup was defined by immunohaematological evaluation with four different commercially available serums. Exons VI and VII of the ABO gene, responsible for 91% of the catalytic active part of the glycosyltransferase, were amplified and subjected to direct sequencing. The results in all samples showed heterozygosity for the G261 deletion. In the A3 allele, the following associations were found: C467T mutation and 1060C deletion in one A3 blood donor and in another G829A and 1060C. In one case, only the 1060C deletion was demonstrated in the A3 allele. One blood donor presented the T646A and the G829A mutations in homozygosity. It was concluded that the A3 blood group is very heterogeneous at the molecular level.

Haemolysis caused by passive ABO antibodies is a rare transfusional complication. We report a case of severe haemolytic reaction in a 38-year-old man (blood group A) with lymphoma who had received one red blood cell (RBC) unit group O. After transfusion of 270 mL, the patient experienced fever, dyspnoea, chills and back pain. On the following morning he was icteric and pale. Haptoglobin was inferior to 5.8 mgdL(-1), haemoglobin was not increased and lactate dehydrogenase was elevated. Haemolysis was evident on observation of the patient's post-transfusion samples. The recipient's red cells developed a positive direct antiglobulin test and Lui elution showed anti-A coated the cells. Fresh donor serum had an anti-A titre of 1024, which was not reduced by treating the serum with dithiothreitol. Donor isoagglutinin screening has been determined by microplate automated analyser and showed titre higher than 100. Physicians should be aware of the risk of haemolysis associated with ABO-passive antibodies. There is generally no agreement justifying the isoagglutinin investigation prior to transfusion. However, automated quantitative isoagglutinin determination could be part of the modern donor testing process, mainly in blood banks where identical ABO group units (platelets or phenotyped RBCs) are not available owing to limited supply.

It is probable that the presence in exon 7 of some of the O02 substitutions could have weakened the enzymatic activity of the encoded B transferase.