Frequency of indeterminate western blot tests in healthy adults at low risk for human immunodeficiency virus infection

As part of a phase 1 trial of a candidate AIDS vaccine, blood specimens were collected from 168 healthy adult volunteers at minimal or no risk for becoming infected with human immunodeficiency virus type 1 (HIV-1). These specimens were screened for evidence of HIV-1 infection by enzyme immunoassay (EIA) and the Biotech/Du Pont Western blot (n = 168), culture (n = 122), and polymerase chain reaction assay (n = 20). None of the subjects had a positive test result by any of these assays, but 32% had indeterminate Western blot tests, most of which demonstrated a single band of lowintensity. The most common bands were p24 (47%), p55 (34%), and p66 (36%); envelope bands were unusual (gp41, 2%; gp120, 2%). No serum specimen collected after 2–11 months from individuals with indeterminate Western blot results was positive by EIA or Western blot. There was91% agreement in the test results ofthe first and second serum samples when the same lot of Western blot kit was used but only 36% agreement when different lots were used. The Biotech/Du Pont Western blot kit thus frequently yields indeterminate test results in the absence of HIV-1 infection, the reproducibility of which is subject to lot-to-lot variability.