Confirmatory Test for Hepatitis C
HCV RNA testing by PCR (polymerase chain reaction) is the confirmatory test for Hepatitis C infection following a positive HCV antibody screening test. 1
Current Standard Approach
The modern diagnostic algorithm prioritizes direct viral detection over older antibody-based confirmatory methods:
HCV RNA testing (quantitative or qualitative) with a detection level of ≤25 IU/mL should be used to confirm active HCV infection after a positive antibody screening test. 1
Ideally, a positive HCV antibody test should automatically reflex to HCV RNA testing, requiring only a single blood collection and avoiding the need for a return visit, which is a major barrier in the continuum of care. 1
HCV RNA detection confirms current, active viral replication and ongoing infection, distinguishing true infection from past resolved infection or false-positive antibody results. 2
Historical Context: RIBA Testing
While recombinant immunoblot assays (RIBA) were previously used as confirmatory antibody tests, they have largely been replaced by HCV RNA testing in modern practice:
Third-generation RIBA tests were developed incorporating antigens from HCV core, NS3, NS4, and NS5 regions to confirm positive ELISA results. 1
A positive RIBA result (reactivity with two or more antigens) correlates with HCV viremia by PCR in 88-98% of cases, but still requires RNA testing to confirm active infection. 1
RIBA indeterminate results (reactivity to only one antigen) are associated with HCV RNA positivity in 58% of cases, necessitating PCR testing regardless. 1
Clinical Context Matters
The need for confirmatory testing depends on the clinical setting:
In patients with chronic liver disease and a positive antibody test, confirmatory PCR testing for HCV RNA is suggested rather than additional antibody-based confirmation. 1
In low-prevalence populations (such as asymptomatic blood donors), false-positive antibody results are more common, making confirmatory testing essential. 1
Signal-to-cutoff (s/co) ratios from screening tests can help predict true positivity: high ratios have a high probability of representing true infection, while low ratios warrant supplemental testing. 1
What HCV RNA Results Mean
Understanding the interpretation is critical for patient management:
Positive HCV RNA = current active infection requiring treatment evaluation. 1, 2
Negative HCV RNA with positive antibody = past resolved infection or false-positive antibody (most commonly past resolved infection). 3
Persons with negative HCV RNA should be informed they do not have evidence of current infection and are not infectious to others. 1, 3
Common Pitfalls to Avoid
Never rely on antibody tests alone to diagnose active HCV infection – antibodies persist indefinitely after viral clearance and cannot distinguish current from past infection. 4
Do not use ALT levels alone to confirm or exclude HCV infection – liver enzymes can be normal despite active viremia or elevated from other causes. 4
In immunocompromised patients or those with recent exposure (<6 months), HCV RNA testing may be needed even with negative antibody results due to delayed or failed seroconversion. 1