FALSE-POSITIVE HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 WESTERN-BLOT TESTSIN NONINFECTED BLOOD-DONORS

Background: The manufacturers' criteria for a positive human immunodef iciency virus type 1 (HIV 1) Western blot (WB) test were recently revi sed to require reactivity to only two of the following bands: p24, gp4 1, and gp120/160. In a recent report, low-risk blood donors were ident ified in whom nonspecific reactivity to multiple env antigens in WB te sting resulted in apparently false-positive WBs by these criteria. The present study was conducted to verify the existence of false-positive WBs among noninfected donors and to assess the extent of this problem . Study Design and Methods: Four donors classified as WB-positive on t he basis of env-only (3 cases) or p24/env-only (1 case) patterns were investigated. Index and/or follow-up specimens were tested by polymera se chain reaction (PCR), by overlapping recombinant env antigens and s ynthetic peptides in enzyme immunoassays, and by deglycosylated and de natured antigen WBs. WB records from American Red Cross blood centers were reviewed to determine the frequency of env-only and p24/env-only patterns, relative to all positive WBs, from 1988 through 1993. Result s: The four index-case donors denied risk and had stable WB reactivity during follow-up. HIV PCR was negative in all. Env reactivity was res tricted to nonglycosylated gp41 epitopes; no gp120-specific reactivity was detected. For three of the four donors, env reactivity was mapped to a 20-amino acid N-terminal epitope of gp41. The rate of detecting WBs with these false-positive patterns increased from 0.6 percent of a ll positive WBs from 1988 to 1990 (4/776) to 8 percent in 1991 and 199 2 (52/683), and then it declined to 6 percent in 1992 and 1993 (47/783 ). Env-only patterns predominated in 1991 and 1992, whereas p24/env-on ly patterns were more frequent following implementation of combined an ti-HIV-1/HIV type 2 enzyme immunoassays in 1992. Conclusion: Low-risk blood donors can have false-positive results on WB tests. Increased de tection of env-only and p24/env-only WBs appears related to the enhanc ed sensitivity of newer enzyme immunoassays to gp41 and p24 antibodies . Donors with these patterns should undergo follow-up testing to docum ent the presence or absence of HIV infection.