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, please visit the AASLD and IDSA HCV guidelines website http://www.hcvguidelines.org.

The US Preventive Services Task Force (USPSTF) and the CDC recommend 1-time universal HCV testing for adults 18 years of age and older, including all pregnant women during pregnancy, in settings where HCV prevalence is >0.1%.^2,3

One-time screening is also recommended for persons with high risk factors or exposures, regardless of age.²

• Persons who have used or are using injection drugs
• Persons who have ever received maintenance hemodialysis and persons with persistently abnormal alanine aminotransferase (ALT) levels
• Recipients of transfusions or organ transplants prior to July 1992
• Persons who have percutaneous or mucosal exposure to HCV-positive blood (eg, occupational needlesticks or sharps injury in a healthcare setting)
• Recipients of clotting factor concentrates produced before 1987
• Persons who were notified that they received blood from a donor who later tested positive for HCV infection
• Persons with HIV; the co-infection rate among this group is 15% to 30%^4,5
• Children born to HCV-positive mothers

Repeat screening is recommended for persons who have ongoing risk for acquiring HCV,² including men who have sex with men (MSM) taking HIV preexposure prophylaxis (PrEP).¹

The testing algorithm starts with an HCV antibody test. Samples with reactive antibodies against HCV should reflex to HCV RNA testing.^6,7 Please refer to the latest recommended CDC testing sequence at 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 infection⁶; no further action is required in most cases. Repeat HCV RNA testing can be considered in those suspected of having recent exposure (within the past 6 months).  

Antibody tests cannot differentiate between acute, chronic, or resolved infection. If distinction between a true positive and a biologic false-positive result for HCV antibody is desired, the CDC suggests considering another HCV antibody assay. If the handling or storage of the test specimen is cause for concern, obtain a new sample for repeat testing.⁶

Yes. Among persons with a non-reactive HCV antibody test and 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.⁶

Additionally, testing for HCV RNA can also be considered in persons who are immunocompromised (eg, persons who are receiving long-term hemodialysis or have been diagnosed with HIV infection).

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 antibody and thus undergo reflex testing for HCV RNA.

Analysis of internal data that included approximately 200,000 specimens submitted to Quest Diagnostics for HCV antibody testing with reflex to HCV RNA testing demonstrated that the frequency of positive reflex results increases with increasing S/C ratio (Graph).

HCV RNA results are reported in IU/mL (abbreviation for international units per milliliter) 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 polymerase chain reaction (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.^8,9 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.

The reportable range for the Hepatitis C Virus RNA, Quantitative Real-Time PCR (TC 35645) is 15 to 100,000,000 IU/mL (1.18-8.00 log IU/mL).

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 detected, 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 Detected IU/mL” is provided.

Quantitative HCV RNA testing is recommended prior to starting DAA therapy and 12 or more weeks after completion of therapy to document sustained virologic response (SVR).¹ Routine monitoring with HCV RNA testing during treatment is not recommended in patients with adherence to treatment.