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2.0 Diagnostic Strategies

Posted in: HCV

2.1 Types and uses of HCV diagnostic tests – also called in-vitro Diagnostic Devices (IVDs)

All tests for HCV must be included on the Australian Register of Therapeutic Goods (ARTG) prior to their use in Australia.  Inclusion on the ARTG requires pre-market assessment of the IVD commensurate with the purpose for which the test is used.

Screening tests

Screening tests may be used by laboratories performing diagnostic testing or screening of blood donations to identify samples that are HCV antibody (anti-HCV) negative. Those samples yielding non-reactive results do not need to be further tested unless clinical considerations demand it. Reactive samples must be subjected to supplemental testing to distinguish true reactivity from false.

Supplemental tests

Supplemental tests are used by laboratories to conduct confirmatory or additional testing to define a sample’s status by distinguishing true from false reactivity. Usually this testing is conducted within a diagnostic strategy and a second immunoassay is used; other supplemental testing situations occur (e.g. in a setting of possible seroconversion illness) when the first-used supplemental tests may include nucleic acid tests.

The supplemental testing must confirm the presence of specific antibody, antigen or viral RNA before the result is accepted as a true positive.

Other tests may be used once the HCV status is confirmed. These include tests to quantify viral load and characterise the virus genotype. 

2.2 Testing for HCV

This section provides advice on minimum standards for laboratory diagnosis and investigation of HCV.  It should be noted that, because of their unique requirements, blood services have developed their own strategies for screening donations. Laboratory investigations are directed towards answering one or more of the following questions:

  1. Has the person ever been infected with HCV? This should be determined by testing for HCV antibodies, or antigen and antibodies simultaneously. RNA testing will be negative in past infection with clearance.
  2. Does the person have current infection? This is determined by testing for HCV RNA or infrequently HCV antigen, as the latter is currently less sensitive than HCV RNA testing. Further, there is only one test on the ARTG that detects HCV antigen only.
  3. What is the current level of viral replication?  With current directly acting antiviral (DAA) regimens, the baseline HCV RNA has little impact on the likelihood of achieving a sustained virological response (SVR). However, a pre-treatment baseline quantitative HCV RNA is recommended because it may identify people who are eligible for shorter treatment duration with certain regimens e.g. genotype 1 infection.
  4. What is the infecting virus genotype?  With interferon-based treatment, HCV genotype was a strong predictor of achieving an SVR. Currently with DAA therapy, the genotype determines the drugs to be used. Pan-genotype drug combinations are soon to be released but until then, HCV genotyping must be performed before treatment initiation. It is also required to meet the PBS criteria for the treatment of hepatitis C and must be documented in the patient’s medical history.

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2.3 Diagnostic strategies for HCV

  • Exposure to HCV is determined by testing for HCV antibodies, or antigen and antibodies simultaneously in serum or plasma.
  • A sample non-reactive in the screening immunoassay can be generally regarded as anti-HCV negative.  If doubt exists, repeat the test or consider qualitative HCV RNA testing.
  • Immunoassays that test for the presence of HCV antibody and antigen simultaneously facilitate earlier detection of people with recently acquired HCV infection. This assay can be used to confirm whether reactivity in an antigen/antibody screening test is attributable to the presence of HCV antigen.16
  • A sample reactive in the screening immunoassay must be subject to a minimum of one alternative immunoassay to confirm the result. The alternative immunoassay should include antigens different from the screening test in both specificity, where possible, and method of preparation. Validation using the two tests together should be undertaken to show that samples falsely reactive in the first test are not also falsely reactive in the second. This is necessary because all immunoassays show a degree of false reactivity and it is important to eliminate to the extent possible, false reactivity that is common between two tests that will be used as part of a diagnostic strategy.17A sample reactive in two approved immunoassays can be reported as anti-HCV positive.
  • Current HCV infection is determined by qualitative testing for HCV RNA or infrequently HCV antigen testing.

−        The manufacturers of quantitative HCV RNA assays specify that they are not for use as diagnostic tests to confirm the presence of HCV infection. Qualitative RNA testing will be negative in past infection with clearance.

−        Ideally, a second blood sample specifically for HCV RNA testing should be used, in line with NPAAC guidelines for nucleic acid testing (NAT). If not available, then blood or plasma should be set aside at the time of sample collection to allow for any subsequent HCV RNA assay to be done if anti-HCV is confirmed positive. The latter may be achieved by dividing a single specimen to allow the two separate tests to be done as appropriate. This procedure may save additional blood collection/processing for people being tested for HCV notwithstanding significant changes that would be required to laboratory workflow if dividing a single specimen were implemented.

−        HCV antigen assays are not currently used regularly in clinical practice. Instead, NAT is the more usual option chosen due to the lower sensitivity of HCV antigen assays. This situation may be influenced in the future by changes in test platforms.

  • HCV genotyping must be performed before treatment initiation, as it determines the regimen and the duration of therapy. 

2.4 Monitoring Treatment

The introduction of the highly efficacious and well tolerated DAAs for the treatment of HCV has reduced the need for frequent on-treatment monitoring of patients. Eligibility for treatment requires a baseline viral load (quantitative HCV RNA test) and HCV genotyping, as most current treatment regimens are genotype specific.  Generally, routine on treatment assessment of HCV RNA levels is not necessary due to the lack of a role for response-guided therapy. In practice, many patients have an assessment at week 4 of therapy during an 8- or 12-week course, as this can give an indication of patient adherence and/or drug efficacy. Patients on 24-week treatment regimens will also require an assessment at week 12. Qualitative HCV PCR testing at the end of treatment can be performed to determine an end-of-treatment response. A further qualitative HCV PCR test is recommended 12 weeks after the end of DAA therapy to confirm successful viral eradication, also known as a sustained viral response (SVR12), which is defined as an undetectable HCV RNA.

Patients who may require more intense monitoring include those in whom adherence is a concern, patients on ribavirin-containing regimens and people with advanced liver disease (portal hypertension or hepatic decompensation).

For more details on testing frequency and type, see Section 6 of the Australian Recommendations for the Treatment of Hepatitis C Infection: a Consensus Statement 2016 available at www.hepcguidelines.org.au

Quick links to resources on this page

Hepatitis C Virus (HCV) Antigen Tests

National Serology Reference Laboratory

16. Australasian Society for HIV Medicine (ASHM). Hepatitis C virus (HCV) Antigen Tests. 22.9.2011. Available at: http://www.ashm.org.au/images/HCV_Testing_portal/Hepatitis_C_virus_(HCV)_Antigen Tests.pdf (Cited 23 March 2012).

17. National Reference Laboratory (NRL) [internet]. Available at: http://www.nrl.gov.au/ Publications+&+Presentations/Publications (Cited 23 March 2012).

 

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