Best Laboratory Test to Screen for HCV Infection
The anti-HCV antibody test using enzyme immunoassay (EIA) or chemiluminescence immunoassay (CIA) is the best initial laboratory test to screen for hepatitis C virus infection in adults. 1, 2
Initial Screening Test
Third-generation enzyme immunoassays (EIA-3) are the recommended first-line screening tests, using recombinant HCV proteins from core, NS3, NS4, and NS5 regions with sensitivity of 97.2-99% and specificity of 99.8-100% in immunocompetent individuals. 1
Enhanced chemiluminescence immunoassay (CLIA) or electrochemiluminescence immunoassay (ECLIA) platforms are increasingly used as they detect antigen-antibody reactions more sensitively than third-generation EIAs. 1
Point-of-care rapid antibody tests using saliva or fingerstick blood (producing results within 20 minutes) have similar sensitivity and specificity to laboratory-based EIA and can be used for screening, particularly in settings where immediate results facilitate linkage to care. 1, 2
Critical Next Step: Reflex HCV RNA Testing
After any reactive (positive) anti-HCV screening test, immediately order HCV RNA testing on the same blood sample to distinguish current active infection from past resolved infection or false-positive results. 1, 2, 3
This reflex testing approach is essential because anti-HCV antibodies persist indefinitely after infection (whether chronic or resolved) and cannot differentiate current from past infection. 1
Among populations with HCV prevalence <10% (general population, blood donors, healthcare workers), approximately 35% (range 15-60%) of positive screening tests are false-positives, making confirmatory testing mandatory. 1
Interpretation Algorithm
If Anti-HCV Positive + HCV RNA Detected:
- Confirms current active HCV infection requiring medical evaluation and antiviral treatment consideration. 2, 3
If Anti-HCV Positive + HCV RNA Not Detected:
- Indicates either past resolved infection (15-45% of infected individuals spontaneously clear the virus) or false-positive antibody test. 2, 3
If Anti-HCV Negative:
- Generally excludes HCV infection, but see special circumstances below. 1
Special Populations Requiring Modified Approach
Immunocompromised Patients (Hemodialysis, HIV, Transplant Recipients):
- HCV RNA testing should be the primary diagnostic test, as anti-HCV may be falsely negative due to impaired antibody response despite active infection. 1, 2, 3
- False-positive rates are lower (~15%) in immunocompromised populations, but false-negatives are more concerning. 1
Suspected Acute HCV Infection or Recent Exposure (<6 months):
- Include HCV RNA testing in the initial evaluation because seroconversion takes an average of 8-9 weeks, and only ~50% of acute HCV patients are anti-HCV positive at initial presentation. 1, 2
- HCV RNA becomes detectable before antibodies appear during acute infection. 2
Persons at Risk for Reinfection After Previous Clearance:
- Use HCV RNA as the primary screening test since anti-HCV remains positive indefinitely after any prior infection, making antibody testing uninformative. 2
Common Pitfalls to Avoid
Never report a reactive anti-HCV screening test as "positive for hepatitis C" without RNA confirmation—this represents only presumptive infection and leads to unnecessary psychological harm and medical visits for false-positive cases. 1, 3
Do not order supplemental antibody testing (RIBA) as the confirmatory test—while RIBA was historically used for this purpose, HCV RNA testing is now the preferred and more clinically useful confirmatory test. 1, 2, 3
Do not rely solely on signal-to-cutoff (S/CO) ratios to determine true positivity—while S/CO ratios >3.8 correlate with 95% RIBA positivity, cutoff values vary by equipment platform, and RNA testing remains necessary. 1
In patients with clinical evidence of liver disease or elevated transaminases but negative anti-HCV, consider direct HCV RNA testing to exclude infection in immunocompromised states or very early acute infection. 1, 3