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Background: Hepatitis C virus (HCV) antigen and antibody combination assays have been launched as a cost-effective alternative to nucleic acid testing (NAT) for early diagnosis by reducing the window period. This study evaluated the clinical performance of HCV antigen/antibody combination assays during window period using HCV seroconversion panels followed by NAT for ELISA reactive samples.
Methods: The performance of the Monolisa HCV antigen-antibody Ultra (Monolisa, Bio-Rad) and the Murex Ag/Ab test (Murex, Abbott) were compared by using two sets of serially diluted commercial HCV seroconversion panels [Genotypes (Gt) 1a & 2b]. Moreover, both assays were used to screen HCV co-infection in filter dried serum spots (DSS) of newly diagnosed HIV-cases (n=1683). All samples positive for both tests were evaluated in the quantitative RT-PCR (qRT-PCR) developed to amplify the 5ยด non-coding region of HCV genome.
Results: For lower dilutions of HCV seroconversion panels, the Murex detected HCV infection 9 (Gt 1a) and 2 (Gt 2b) days earlier than the Monolisa. However, Murex showed fluctuating and lower OD values below the cut-off for higher dilutions until days 28 (Gt 1a) and 135 (Gt 2b) compared with the Monolisa which showed a progressive increase in the OD value for all dilutions in each panel. Accordingly, 219/1683 (12.9%) and 193/1683 (11.4%) DSS samples were found positive in the Murex and Monolisa, respectively. Further testing of ELISA reactive samples by qRT-PCR revealed 167 NAT positive results. Of these, 74 (44.3%) were also positive for both, the Murex and Monolisa. Moreover, 10/167 (5.9%) of samples positive in the HCV RNA assay were only positive in the Monolisa while 5/167 (2.9%) were only positive in the Murex ELISA.
Conclusions: The Monolisa provides more reliable results for the detection of HCV infections in all dilutions compared to the Murex indicating its potential use for HCV screening in DSS. However, with its reactivity at earlier days of HCV infection, the Murex may serve as an additional diagnostic tool in HIV/HCV co-infected patients to narrow the window period. Moreover, the application of NAT on ELISA positive samples can be used to confirm early infections and to distinguish between active/chronic and resolved HCV infections.