EMERGING TESTS

Novel HCV Antigen Test Allows 1-Step Screening, Diagnosis

A novel hepatitis C virus antigens enzyme immunoassay (HCV-Ags EIA) can reliably serve as a one-step test to screen and diagnose active or viremic HCV (V-HCV) infection, according to a study published online June 6 in Hepatology. The highly specific and sensitive test relies on simultaneous detection of four HCV proteins and non-denaturation of serum samples to achieve results comparable to HCV RNA reverse transcription-polymerase chain reaction (RT-PCR) results in differentiating V-HCV infection from resolved HCV (R-HCV) infection.

While the latest generation of anti-HCV tests are highly sensitive and specific, they are relegated to screening tests as they remain incapable of diagnosing acute HCV infection and differentiating between V-HCV and R-HCV infection. The gold standard for HCV diagnosis remains HCV RNA RT-PCR, which is costly and requires specialized equipment not available in low-resource settings. The availability of new treatment options are increasing the need for HCV screening and diagnosis to link these individuals to appropriate care. HCV core antigen (HCVcAg) has been considered a serologic marker of viral replication and holds promise for one-step diagnosis of HCV infection, but HCVcAg-based tests have been plagued by low sensitivity and specificity.

To develop the HCV-Ags EIA the researchers first assessed the expression and detectability of the HCV non-structural proteins, other than HCVcAg in HCV-infected serum specimens (HCV NS3, NS4b and NS5a). These HCV proteins are expressed in all six HCV genotypes. For comparison, anti-HCV test was performed using the Architect Anti-HCV Assay, a chemiluminescent microparticle immunoassay (Abbott Laboratories) and serum HCV RNA was quantitated by real-time RT-PCR using the Roche COBAS AmpliPrep/COBAS TaqMan HCV assay.

The University of California Irvine researchers found their novel HCVAgs EIA has high specificity and sensitivity for detection of V-HCV infection. Furthermore, sample non-denaturation is needed to guarantee specificity high enough to diagnose V-HCV. In 189 cases with V-HCV infection by all six different genotypes, three with acute HCV infection, and 186 with chronic V-HCV infection, there was 100 percent positivity concordance between the results of HCV-Ags EIA and HCV RNA RT-PCR. Additionally, the HCV-Ags EIA could diagnose acute HCV infection 59 days to 65 days before anti-HCV appearance.

“For the first time, we demonstrated that serum sample denaturation is the main reason for the low specificity of HCV-Ags related tests, including current HCVcAg assays, and results in failure to differentiate V-HCV infection with R-HCV infection. As most reported HCVcAg assays employ pre-test serum sample denaturation to increase the test sensitivity, these current HCVcAg tests cannot be used for onestep diagnosis of V-HCV infection,” writes co-author Ke-Qin Hu, M.D. “Our data support further clinical development of this novel HCV-Ags EIA assay as a cost-effective and convenient one-step alternative clinical assay for HCV screening and diagnosis to replace the current two-step approach.”

Hu tells DTET that the technology has been exclusively licensed to DiligenMed (Irvine, Calif.). He expects that following an additional clinical trial, and once the test subsequently becomes available, it can replace the current two-step approach to hepatitis C screening and diagnosis—promoting universal screening and diagnosis of HCV infection.

Takeaway: Simultaneous detection of four HCV-Ags in a novel EIA that uses non-denaturation of serum samples may eliminate the need for two-step testing for HCV.

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