The significance of repeat testing in Turkish blood donors screened with HBV, HCV and HIV immunoassays and the importance of S/CO ratios in the interpretation of HCV/HIV screening test results and as a determinant for further confirmatory testing

Abstract

The purpose of this study was to investigate the intra-assay correlations amongst initial reactive and repeat screening results used in enzyme immunoassays (EIAs) for hepatitis B virus (HBV), hepatitis C virus (HCV) and HIV in blood donors. This study evaluated the value of using the power of the signal to cut-off (S/CO) ratio index for confirming anti-HCV/HIV reactive screening results, thereby touching upon the utility of S/CO indices in determining whether further confirmatory testing was necessary. Screening test results of the 72,695 blood donors were evaluated over a 1-year period. Correlation analysis among each initial test and retests was done by Pearson r test. Appropriate S/CO values to determine the need of the confirmation testing was investigated by ROC analyses. EIA intra-assay correlations were of statistical significance and were determined as follows: 0.948 for anti-HCV, 0.827 for anti-HIV and 0.948 for HBsAg. The threshold S/CO ratio values which predicted more than 95% of the confirmation test result were 3.8 for HCV and 5.6 for HIV. We were able to demonstrate a strong level of intra-assay correlation amongst EIAs, thereby eliminating the need for repetition of the screening test. Hence, we suggest that repeat screening should only be limited to HBV and HIV tests with low EIA S/CO ratios. Thus, using the power of the S/CO ratio in determining the need for HCV confirmation testing can be a cost-effective measure, especially if the S/CO value is >or=3.8.

Comparison Between Screening and Confirmatory Serological Assays in Blood Donors in a Region of South Italy

“…Our results indicate that it is possible to define S/CO values for each ARCHITECT assay with a PPV that nears 100%, as already demonstrated by Kiely et al and by Acar et al for other assay systems. However, if these S/CO values were used to discriminate confirmed positive samples from BFP without confirmatory testing, a substantial percentage of specimens would be incorrectly classified.…”

“…This approach has been employed in many previous studies on anti-HCV, and most of them have indeed demonstrated the relationship between high S/CO values and serological confirmation of anti-HCV positivity (9,(14)(15)(16)(17) and even with HCV viremia (14,18). Thus, a higher S/CO ratio for anti-HCV is deemed to guarantee a higher PPV, but the data on the other screening assays are less common (10,11,19), and we believe that ours is one of the first systematic attempts in this direction, although it has been carried out on a relatively small number of blood donations.…”

Screening for hepatitis C virus infection in a high prevalence country by an antigen/antibody combination assay versus a rapid test

“…Nevertheless, two tests increase the cost of the screening unless a sequential screening strategy is used (Seed et al, 2003). Another solution would be to use the strength of antibody reactivity as predictive marker of true-positive results and viremia in asymptomatic HCV infected people (Acar et al, 2010; Contreras et al, 2010; Kiely et al, 2010; Stramer et al, 2012). Our results, from an admittedly small study, are in accordance with this last report since mean s/co ratios were significantly higher in viremic subjects.…”

A Signal-to-Cutoff Ratio in the Abbott Architect HIV Ag/Ab Combo Assay That Predicts Subsequent Confirmation of HIV-1 Infection in a Low-Prevalence Setting

“…Other studies with small samples have suggested a relationship between the S/CO ratio in HIV Ag/Ab assays and confirmed HIV infection or the HIV viral load (VL) (1,(6)(7)(8). As the somewhat time-consuming HIV WB test is the currently approved confirmatory test in Australia, we assessed the positive predictive value of the Abbott Combo assay in this low-prevalence population.…”