ObjectivesTo evaluate the diagnostic accuracy of the test for antibodies to hepatitis C virus by enzyme-linked immunosorbent assay (anti-HCV ELISA-2) in patients with and without HIV-1 infection.DesignCohort study.MethodsIn all, 369 patients were tested and grouped by available serologic tests. HCV RNA was quantified in these 369 patients using an Amplicor HCV (and/or HIV-1) Monitor, v1.0 test. Among 110 patients who were anti-HCV negative by ELISA-2, 39 were HIV/HBV coinfected and 71 had HIV alone. One hundred twelve patients were HIV/HCV coinfected and 147 patients had HCV infection alone.ResultsSix of 110 (5.5%) ELISA-2 anti-HCV–negative, HIV-infected patients had circulating serum HCV RNA. Their median CD4 count was 36 cells/mm3, which was significantly lower than that observed in the HIV/HBV group (median CD4 = 109,p< .001) or the HIV/HCV cohort (CD4 = 235;p< .0001). The positive predictive value of the ELISA-2 test for diagnosing ongoing HCV infection in HIV-infected patients was 91%, which is significantly better than that determined for the HCV group, 76% (p= .002) presumably because HCV is less likely to resolve in the HIV patients. Mean alanine aminotransferase (ALT) levels were similar in the HIV/HCV (133 IU/L) and HCV (130 IU/L) cohorts. Median HCV RNA levels were higher in the HIV/HCV group (6.53 log10copies/ml) compared with the patients with HCV infection (5.62 log10copies/ml;p< .00001). There was no significant correlation between HCV RNA levels and ALT values, CD4 counts, or HIV RNA concentrations.ConclusionsThe predictive value of the anti-HCV ELISA-2 test is better in HIV-coinfected patients than in patients infected only with HCV. False negative results, usually associated with acute infection or with low CD4 counts, are uncommon. These patients may be diagnosed with the ELISA-3 assay or by reverse transcriptase polymerase chain reaction (RT-PCR). Compared with patients with only HCV infection, HIV/HCV patients display similar ALT profiles, but a higher proportion of detectable serum HCV RNA.