Use of the hepatitis C virus core antigen (HCVcAg) assay may be an alternative to nucleic acid testing (NAT) for screening active HCV infection in areas where access to virological diagnosis and therapeutic monitoring is limited, according to a study in The Journal of Molecular Diagnostics.
“Simplified, affordable tools to diagnose active hepatitis C virus (HCV) infection are needed to scale up treatment,” wrote authors led by Tanya L. Applegate, PhD, the Kirby Institute, University of New South Wales, Sydney, Australia.
While effective treatment for HCV exists, many people go untested, even in affluent countries such as the United States. The status quo for HCV testing is either serologic assays (ie, antibodies to HCV) or nucleic acid testing (NAT). Although NAT is more sensitive than serologic assays, it’s also more expensive.
HCVcAg, a stable protein released during virus assembly, can be used to detect HCV more cheaply, with a shorter assay time, than NAT. Although HCVcAg sensitivity is lower than that of NAT, this sensitivity becomes comparable between assays when HCV RNA plasma levels are high, as is the case during chronic infection. (More than 95% of patients with chronic HCV infection have HCV RNA greater than 10,000 IU/mL.)
The World Health Organization (WHO) recently recommended dried blood samples (DBS) collected via finger stick to test for hepatitis B virus (HBV) and HCV. DBS facilitates sample collection, storage, and shipment, which makes this diagnostic approach viable for lower-income countries with limited HCV testing resources. In higher-income countries, DBS could help marginalized populations access HCV testing. Also, DBS doesn’t require direct venous access, which makes testing intravenous drug abusers easier.
For this investigation, Dr. Applegate and colleagues analyzed the sensitivity and specificity of HCVcAg testing in 120 paired plasma and DBS samples, of which 95 samples exhibited quantifiable HCV RNA levels. They tested sensitivity and specificity at two HCV RNA thresholds: ≥15 IU/mL and ≥3,000 IU/mL.
The HCVcAg assay had better sensitivity and specificity in plasma than in dried blood samples, the researchers found. In plasma samples with HCV RNA ≥3,000 IU/mL, sensitivity was 97.7% (95% CI = 91%-100%) and specificity was 100% (95% CI = 87%-100%). Corresponding DBS sensitivity was 88.6% (95% CI = 80%-94%) and specificity was 97% (95% CI = 82%-100%).
In plasma, the researchers detected HCVcAg in 98% of samples with HCV RNA levels more than 3,000 IU/ml, and did not detect HCVcAg in 97% of samples with levels less than 3,000 IU/ml. Comparatively, they were able to detect HCVcAg in 97% of DBS samples with HCV RNA levels more than 3,000 IU/mL, and were unable to detect HCVcAg in all DBS samples with levels less than 3,000 IU/mL.
“Although the potential impact of amino acid mutations within the HCV core region remains unclear, this preliminary study suggests the detection of active infection by HCVcAg from DBS may provide sufficient specificity and sensitivity as a screening tool for chronic HCV infection and warrants further research,” the authors wrote.
This study had limitations. For instance, the sample size of the study was small, with mostly HCV genotype 1 and genotype 3 analyzed.
“The data from this study demonstrate a good sensitivity and specificity of HCVcAg in plasma when HCV RNA >3,000 IU/mL,” the researchers concluded. “The level of HCVcAg quantified in plasma was higher than that in DBS.”
This study was funded by the Kirby Institute.