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Because large numbers of volunteer blood donors may be disqualified for "false-positive" results on tests for antibody to hepatitis B core antigen (anti-HBc), a more specific definition of anti-HBc enzyme immunoassay (EIA)-reactive was evaluated, including only those donor samples that were "strongly" reactive (sample-to-cutoff absorbance ratio, < 0.45). Results using this definition and other anti-HBc test methods were compared to the serologic response (antibody to hepatitis B surface antigen [anti-HBsAg]) to hepatitis B vaccination. Fifty-eight volunteer blood donors who had previously been deferred as donors, because of reactive anti-HBc tests (all other blood screening tests were negative, including those for HBsAg and anti-HBsAg) on two occasions, were vaccinated for hepatitis B. It was assumed that an anamnestic response to vaccine indicated past infection with hepatitis B, while a primary response to vaccine indicated lack of past infection. One (2%) of 43 donors with a historically "weak" anti-HBc (reactive absorbance ratio, > or = 0.45) had an anamnestic response to vaccine, compared to 8 (53%) of 15 with historically "strong" anti-HBc (reactive absorbance ratio, < 0.45) (p < 0.005). Anti-HBc testing using the microparticle EIA method also correlated well with hepatitis B vaccination results. The use of a narrower definition of "reactive" for anti-HBc EIA testing yielded much more specific, but slightly less sensitive, results.

A study was undertaken to determine the prevalence and risk factors for serological evidence of hepatitis C virus (HCV) infection in patients infected with the human immunodeficiency virus (HIV). Tests for anti-HCV antibody were carried out by enzyme-linked immunoassay (EIA) on 101 HIV-infected patients from two university-based outpatient clinics. Anti-HCV antibody reactive samples were tested by using a recombinant immunoblot assay (RIBA) for HCV antibodies. Fourteen of 101 (13.9%) HIV-infected patients were anti-HCV reactive by EIA. Of these 14, only seven were reactive by RIBA: four were intravenous drug users as a sole risk factor for HIV infection; and the remaining three acquired HIV by blood transfusion, contaminated instrument exposure or IV drug use and sexual contact. Acquisition of HIV by sexual activity alone was not associated with HCV infection. It is concluded that HCV infection is found in approximately 7% of a university HIV clinic population. False-positive anti-HCV antibody serology may lead to overestimation of the prevalence of HCV infection. Female sex and intravenous drug use are significantly associated with HCV infection among HIV-infected individuals.

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