Factors associated with positive direct antiglobulin tests in pretransfusion patients: a case-control study.

During routine pretransfusion testing, the presence of IgG on patient red cells is suggested by a positive autocontrol and confirmed by a positive direct antiglobulin test (DAT) using monospecific anti-IgG sera. Most IgG on patient red cells detected in this manner are of unknown etiology. We recently showed an association between elevated serum globulin levels and positive DAT with unreactive eluate in patients with acquired immunodeficiency syndrome (AIDS). In the present study, we wished to determine whether elevated serum globulin levels contribute to some of the positive DAT encountered in pretransfusion testing of patients without AIDS. 76 patients with positive DAT were compared with 90 controls without IgG detected on their red cells during pretransfusion testing. The rate of elevated serum globulin levels was 75% in positive DAT cases versus 29% in controls (p less than 0.001); the odds ratio was 7.6. Elevated blood urea nitrogen levels occurred in 42% of cases versus 19% of controls (p less than 0.025); the odds ratio was 3.1. Cases and controls were not significantly different with regard to age, sex, race, quinidine usage, or hyperalimentation. Elevated serum globulin and blood urea nitrogen levels are significantly associated with a positive DAT with unreactive eluate in pretransfusion patients.