What is the diagnostic workup algorithm for hepatitis C?

Hepatitis C Diagnostic Workup Algorithm

The diagnosis of hepatitis C infection requires a two-step approach: initial screening with anti-HCV antibody testing followed by confirmatory HCV RNA testing to identify active infection. 1

Initial Screening

• First-line test: Anti-HCV antibody detection by enzyme immunoassay (EIA) 1
  • Alternative screening options:
    • Rapid diagnostic tests (RDTs) using serum, plasma, fingerstick whole blood, or oral fluid 1
    • Dried blood spots (DBSs) for remote testing 1

Confirmatory Testing

• If anti-HCV antibody positive: Test for HCV RNA using a sensitive molecular method (lower limit of detection <15 IU/ml) 1
  • Alternatively, HCV core antigen testing if HCV RNA testing is unavailable or unaffordable 1
  • Reflex testing (automatic HCV RNA testing on the same sample used for antibody testing) is recommended to improve linkage to care 1

Special Situations

• Suspected acute hepatitis C: Test directly for HCV RNA as antibodies may not be detectable in early infection 1

  • Acute infection is suspected with:
    • ALT >10 times upper limit of normal
    • Jaundice
    • Recent exposure risk
    • Absence of history of chronic liver disease 1

• Immunocompromised patients: Test for HCV RNA even if antibody-negative 1

• Anti-HCV positive, HCV RNA negative results: Retest for HCV RNA after 3 months to confirm true clearance 1

Interpretation of Results

1. Anti-HCV positive, HCV RNA positive: Current HCV infection (acute or chronic) 1

   • Chronic infection is diagnosed if viremia persists beyond 6 months 1

2. Anti-HCV positive, HCV RNA negative:

   • Resolved HCV infection
   • False-positive antibody test (especially in low-prevalence populations)
   • Early acute infection (in "window period") 1

3. Anti-HCV negative, HCV RNA positive:

   • Early acute infection
   • Chronic infection in immunosuppressed patient 1

Common Pitfalls to Avoid

• Relying solely on antibody testing: This cannot distinguish between active infection and resolved infection 1

• Missing acute infections: HCV RNA appears before antibodies in acute infection; testing only for antibodies may miss early cases 1

• False-positive antibody results: More common in low-prevalence populations; confirmatory RNA testing is essential 2, 3

• Using denaturation in HCV antigen assays: This decreases test specificity due to release of HCV antigens from immune complexes 4

• Inadequate sensitivity of dried blood spots for HCV core antigen: DBSs should not be used for core antigen testing as false-negative results occur in 7-36% of viremic patients 1

By following this diagnostic algorithm, clinicians can accurately identify patients with active HCV infection who require treatment to prevent progression to cirrhosis, hepatocellular carcinoma, and death.