Patient ABO blood type is a major predictor of a positive DAT following a transfusion reaction

A direct antiglobulin test (DAT) checks for antibody or complement on the surface of RBCs and is often done following a transfusion reaction. While passive anti-A and anti-B antibodies are known to cause positive DATs, the extent this occurs following transfusion is unknown.

DAT results, ABO type, eluate information, and blood product information were recorded on 1097 transfusion reactions at a large academic hospital over 8 years. The effect of patient blood type, product type, and plasma compatibility of blood product transfused on DAT results were determined. Statistical significance was determined using Chi-squared testing.

Patient ABO blood type was a strong predictor of a positive DAT, with type O patients having 6.7% positive rate and non-O patients having a positive rate of 20.6% (p < .0001). Plasma compatibility of the product was a strong predictor of a positive DAT, with plasma compatible transfusions having a 9.4% positive rate while plasma incompatible transfusions were positive 44% of the time (p < .0001). Elution studies found that anti-A/B antibodies were the most common antibody identified. Platelets were more likely to be associated with a positive DAT when compared with RBC transfusions (p < .05).

These results demonstrate the patient ABO type and plasma incompatibility are strong predictors of positive DAT results following a transfusion reaction. Anti-A and anti-B antibodies are estimated to account for about 50% of positive DATs in this study.