What is the recommended laboratory testing sequence for diagnosing hepatitis C (HCV) infection?

Recommended Laboratory Testing Sequence for Hepatitis C Diagnosis

The recommended laboratory testing sequence for diagnosing hepatitis C (HCV) infection is to order HCV-antibody testing with reflex HCV RNA polymerase chain reaction testing for initial HCV screening. 1

Initial Testing Algorithm

1. First-line test: HCV antibody test

   • Use an FDA-approved assay (laboratory-based or point-of-care)
   • Order as "HCV antibody with reflex to HCV RNA" to avoid requiring a second blood draw 1
   • This approach requires only a single blood collection and prevents loss to follow-up 1

2. Interpretation of HCV antibody results:

   • Nonreactive: No HCV antibody detected (no current or past infection in most cases)
   • Reactive: Indicates one of three possibilities:
     • Current HCV infection (acute or chronic)
     • Past, resolved HCV infection
     • False positive result 1

3. Reflex testing for reactive antibody results:

   • All reactive HCV antibody tests should automatically reflex to HCV RNA testing 1
   • HCV RNA testing confirms active infection and distinguishes between current infection and resolved/false positive results

Special Testing Considerations

• Recent exposure (within 6 months):

  • Consider direct HCV RNA testing or follow-up HCV antibody testing 6+ months after exposure 1
  • HCV antibody may not be detectable during this "window period"

• Immunocompromised patients:

  • Consider direct HCV RNA testing as these patients may have false-negative antibody results 1, 2

• Persons at risk for reinfection:

  • Use HCV RNA testing directly (antibody will remain positive from previous infection) 1

• Distinguishing false positives from resolved infection:

  • If clinically important, consider testing with a second, different HCV antibody assay 1
  • Different assays vary in antigens, platforms, and performance characteristics 1

Pre-Treatment Testing

If HCV RNA is detected (confirming current infection), additional testing is recommended:

1. Quantitative HCV RNA testing:

   • Documents baseline viral load before starting treatment 1

2. HCV genotype testing:

   • May be considered if it would alter treatment recommendations 1

3. Additional recommended tests:

   • Liver function tests (AST/ALT, alkaline phosphatase, bilirubin, albumin)
   • Complete blood count
   • Prothrombin time/INR
   • Testing for coinfections (HBV, HIV) 2

Common Pitfalls to Avoid

• Incomplete testing: Ordering only HCV antibody without reflex to RNA testing leads to diagnostic delays and loss to follow-up 1

• Misinterpreting positive antibody tests: A positive antibody test alone doesn't confirm current infection 1

• Missing acute infections: Relying solely on antibody testing in recently exposed individuals may miss early infections 1

• Inadequate specimen handling: Improper storage or handling of specimens for HCV RNA testing can lead to false negative results 1

• Failing to educate patients: Patients with positive antibody but negative RNA should understand they are not currently infected but remain susceptible to reinfection 1

By following this evidence-based testing algorithm, clinicians can accurately diagnose HCV infection, enabling appropriate treatment decisions that reduce morbidity and mortality from chronic hepatitis C.