Confirmatory Testing for Hepatitis C Infection
Introduction to HCV Testing
- The American Association for the Study of Liver Diseases recommends HCV RNA testing by PCR as the confirmatory test for Hepatitis C infection following a positive HCV antibody screening test 1
- 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 1
Interpretation of HCV RNA Results
- A positive HCV RNA result confirms current, active viral replication and ongoing infection, distinguishing true infection from past resolved infection or false-positive antibody results 2
- 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) 7
Clinical Context and Testing
- 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 3, 5
- In low-prevalence populations (such as asymptomatic blood donors), false-positive antibody results are more common, making confirmatory testing essential 3, 6
- 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 6
Avoiding Common Pitfalls
- Never rely on antibody tests alone to diagnose active HCV infection – antibodies persist indefinitely after viral clearance and cannot distinguish current from past infection 8
- 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 8
- 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