Hepatitis C Virus Antibody and RNA Testing

HCV management guidelines are provided by the American Association for the Study of Liver Diseases (AASLD) and the Infectious Disease Society of America (IDSA).¹ These organizations publish joint, evidence-based recommendations on the Internet for rapid formulation and dissemination. For more information, visit http://www.hcvguidelines.org.

The US Preventive Services Task Force (USPSTF) and the CDC recommend 1-time screening for HCV infection for adults born 1945 through 1965.^2,3 One-time screening is also recommended for adults with high risk due to:

• Injection drug use (current or former)^3,4
• Receipt of transfusions or organ transplants prior to July 1992^3,4
• Having ever received long-term hemodialysis^3,4
• Incarceration³
• Unregulated tattoo(s)³
• Percutaneous (eg, occupational) exposure^3,4
• Receipt of clotting factor concentrates produced before 1987^3,4
• HIV infection; the co-infection rate among this group is 20% to 30%⁵

Screening is also recommended for children born to HCV-positive mothers.^3,4

HCV testing is recommended for individuals with persistently abnormal levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), or bilirubin.^3,4

Please refer to https://www.cdc.gov/hepatitis/hcv/pdfs/hcv_flow.pdf.

A reactive HCV antibody test result combined with a not-detected HCV RNA result indicates no laboratory evidence of a current active HCV infection; no further action is required in most cases.

If distinction between a true positive and a biologic false-positive result for HCV antibody is desired, the CDC suggests that one can consider testing with another HCV antibody assay. If there is concern regarding the handling or storage of the test specimen, obtain a new sample for repeat testing.⁶

Yes. Among persons with a non-reactive HCV antibody test, who are suspected of having liver disease or are at high risk of acute infection, testing for HCV RNA or follow-up testing for HCV antibody is recommended if high-risk exposure to HCV occurred within the past 6 months. Additionally, testing for HCV RNA can also be considered in persons who are immunocompromised (eg, persons who are receiving long-term hemodialysis or are HIV infected).

Among specimens with reactive HCV antibody results, approximately 52% have detectable HCV RNA at a level of >15 IU/mL on reflex testing. However, the frequency varies markedly based on the strength of the signal of the antibody test, or signal-to-cutoff (S/C) ratio. Specimens with an S/C ratio of at least 1.0 are considered reactive for HCV antibody⁷ and thus undergo reflex testing for HCV RNA. Analysis of approximately 200,000 specimens submitted to Quest Diagnostics for HCV antibody testing with reflex to HCV RNA testing demonstrate that the frequency of positive reflex results increases with increasing S/C ratio:

The result “<15 IU/mL, Detected” means that HCV RNA is detected, although at a level (<15 IU/mL) that is too low to be quantified. This result could indicate current active HCV infection if consistent with other clinical and laboratory data. NOTE: If this test is being performed for HCV diagnosis, then this <15 IU/mL Detected result should be confirmed using a second sample from the patient.

In contrast, the result “<15 IU/mL, Not Detected” means that HCV RNA is not detected and there is no evidence of current active infection.

Quest Diagnostics measures HCV RNA viral load with the Roche cobas^® HCV methodology. This is a quantitative real-time PCR assay with a lower limit of quantification (LOQ) of 15 IU/mL; the limit of detection (LOD) is slightly lower, at 10 IU/mL to 13 IU/mL. If the viral load is just at or above this LOD, but less than 15 IU/mL, the assay can determine that HCV RNA is present but cannot provide a reliable quantitative result. In such cases, the qualitative result of “<15 IU/mL, Detected” is provided.

HCV RNA results are reported in IU/mL, which is the abbreviation for international units per milliliter. Results are reported in IU/mL to facilitate comparisons between results generated by different test methods. This is important because the various methods used by different laboratories are not standardized against each other. Use of IU/mL reporting units helps to make the comparison of viral load results across different methods more reliable.

HCV RNA results are also reported in log IU/mL, which is the logarithm of IU/mL. Results in this format make it easier to understand whether a change in viral load is clinically meaningful.

Replicating PCR test results using the same specimen can vary analytically by as much as 0.5 log IU/mL; thus, only changes greater than 0.5 log IU/mL from one measurement to the next (or across several measurements) are considered to represent true changes in viral load.⁸ Reporting the viral load results in log IU/mL units helps the healthcare provider accurately interpret changes in viral load and better assess a patient's response to antiviral treatment.

If HCV RNA is detectable at week 4 of treatment, per AASLD guidelines, it is suggested to repeat quantitative HCV RNA viral load testing after 2 additional weeks of treatment. If quantitative HCV RNA testing at week 6 of treatment shows an increase of greater than 10-fold (>1 log10 IU/mL), discontinuation of HCV treatment is recommended. The cause of a positive HCV RNA test result at week 4, with decreasing levels at week 6 or week 8, is unknown. There is no recommendation to stop therapy or extend therapy for these patients.⁹