What do western blot indeterminate patterns for human immunodeficiency virus mean in EIA-negative blood donors?

To investigate the specificity of western blot indeterminate (WBi) patterns for antibodies to the human immunodeficiency virus type 1 (HIV-1), 100 enzyme immunoassay (EIA) negative donors from whom prospectively obtained recipient sera were available were tested by WB. 20 were WBi, with p24 being the predominant (70%) and generally the only band. Among recipients of WBi blood, 36% were WBi in their 6 month post-transfusion sample, but so were 42% of a control population that had received only WB-negative blood. When serial samples from recipients with a WBi pattern were tested on two occasions, only 35% of results were reproducible. No reciepient of WBi blood became EIA positive, true positive for WB, positive for HIV-1 antigen, or positive for EIA reactivity against recombinant p24 or gp41. The polymerase chain reaction was negative for gag and env HIV-1 sequences in all donors and recipients. Thus WBi patterns are exceedingly common in randomly selected donors and recipients and such patterns do not correlate with the presence of HIV-1 or the transmission of HIV-1 from donor to recipient.