Chemiluminescence assay improves specificity of hepatitis C antibody detection.

BACKGROUND: Antibodies to hepatitis C virus (anti-HCV) have typically been detected by enzyme immunoassay (EIA). A chemiluminescence assay (CA) for anti-HCV is now commercially available. METHODS: We compared the positive rate for a CA in a HCV screening program for veterans with historical rates obtained with EIA. We also compared results in 2824 samples tested by both methods and assessed the significance of low signal-to-cutoff (S/C) ratios. RESULTS: The frequency of CA-positive results was significantly lower than with EIA (12.6% vs 16.0%; P <0.0001). The frequency of low S/C ratios was also significantly lower with CA (11.5% vs 20.0%; P <0.0001). Among low-positive values, samples positive by CA were significantly less likely to be recombinant immunoblot assay (RIBA)-negative (64% vs 84%; P <0.0005). In parallel testing, results for 111 samples (3.9%) were discrepant between the two assays; all but 6 had low S/C ratios, and confirmatory testing was performed on all but 8 samples. Of 56 EIA-positive, CA-negative samples tested by RIBA, only 1 was positive. Of 24 CA-positive, EIA-negative samples, 62% were RIBA-negative. Using a negative RIBA result as an indication of false-positive anti-HCV results, the positive predictive value of EIA was 93% compared with 98% with CA. HCV RNA was positive in 90% of samples high-positive by both CA and EIA. Only 2 of 30 (7%) low-positive CA samples were RNA-positive. CONCLUSIONS: CA produces fewer false-positive and fewer low-positive results that require confirmatory RIBA testing. The S/C ratio remains useful for characterizing positive results.

Low-positive anti-hepatitis C virus enzyme immunoassay results: an important predictor of low likelihood of hepatitis C infection.

BACKGROUND: Tests for hepatitis C antibodies (anti-HCV enzyme immunoassays) are usually described as positive or negative. Several studies, mainly in blood donors, have found that specimens with low signal/cutoff (S/C) ratios are commonly negative when tested with a recombinant immunoblot assay (RIBA) or for HCV RNA. METHODS: We retrospectively reviewed 17 418 consecutive anti-HCV results from a screening program for high-risk veterans; 2986 (17.1%) samples were anti-HCV-positive, and 490 (16.4%) had S/C ratios