The 2009 American Association for the Study of Liver Disease Recommendations for Screening and Counseling include the following:

• A comprehensive health evaluation should include screening for behaviors which increase the risk of HCV infection.
• At risk patients should be tested for HCV
• HCV positive patients should be counseled in techniques to avoid transmission of HCV.
• HCV antibody tests should be employed when a patient is suspected of acute or chronic HCV infection.
• HCV RNA tests should be used to confirm HCV when:
  • HCV antibody test is positive
  • HCV antiviral treatment is considered
  • HCV infection is suspected in immunocompromised patients if antibody tests are negative.

HCV infection is seldom diagnosed during its acute phase. As many as 80 % of infected individuals have no symptoms and no idea that they can transmit the disease. Of those infected, up to 85% may remain asymptomatic for years while the virus slowly destroys liver cells. A diagnosis of chronic hepatitis C is usually made following a work up for complaints of:

• RUQ discomfort,
• fatigue or
• poor appetite.

The first evidence may come from elevated liver functions test and the presence of HCV antibodies (anti-HCV). Tests to detect antibodies to HCV (anti-HCV) were first licensed by the Food and Drug Administration (FDA) in 1990. The CDC recommends that a person be considered positive for HCV infection only after an initial anti-HCV screening test has been verified by a more specific serologic or nucleic acid test (NAT). The verifying test ensures that the original test was not a false positive. If the individuals being tested present with evidence of liver disease, then false positives are very unlikely. However, in symptom-free individuals who are among populations with a low prevalence of HCV, false positives are a matter for concern.

Liver enzyme tests are often used to monitor treatment in conjunction with HCV-RNA tests to determine viral load. Baseline serum viral load levels and infecting genotype help to predict the outcome of therapy and influence the choice of the therapeutic regimen. HCV RNA can be detected in serum or plasma within 1 to 2 weeks after exposure to the virus.

There are 4 different types of tests that are currently used in diagnosis and management of HCV:

• Liver enzyme tests
• Antibody detection tests
• Virus detection tests
• HCV genotyping
  

• Enzyme immunoassay (EIA) or enzyme-linked immunosorbent assay (ELISA)
• Recombinant immunoblot assay (RIBA)
  

• (Ribo) Nucleic acid tests (NATs): quantitative and qualitative
• Branched chain DNA
• Total HCV Core Antigen
  

Nucleic acid tests (NATs)

Nucleic acid tests (NAT) that detect HCV RNA can be used for diagnosis of acute and chronic HCV infection and for the evaluation and management of patients with chronic hepatitis C. NATs have the advantage of detecting active HCV infection and verifying the presence of antigens.

There are 2 types:

• Quantitative
• Qualitative
  
  Quantitative HCV RNA tests detect the presence of the virus itself and measure the amount in the plasma; the viral load. There are numerous tests available, and a positive finding is accepted as proof of HCV infection. HCV RNA tests are usually done at intervals to measure the effect of anti-viral therapy:
  • 12 weeks
  • 24 weeks
  • End of treatment
  • 6 months after treatment completed
    
  Qualitative HCV RNA tests are used to detect virus in the blood. They are highly sensitive to the presence of HCV RNA but do not calculate the viral load. The results are expressed as positive or negative and can detect 100 to 1000 copies of the virus. Newer tests will detect less than 50 copies per milliliter. Because they are more sensitive than quantitative tests, they can detect the virus earlier, which may be of use when a known exposure occurs.
  It is possible to get a negative test result for HCV RNA during the acute phase of HCV infection when the antigen level is low. The newest qualitative tests can detect the presence of < 50 copies/ml of HCV RNA, usually within 1-2 weeks of infection. Therefore, while possible, a false negative result is increasingly unlikely.
  The significance of the absolute values of viral load has not yet been fully determined, so clinical decisions are usually made on the basis of "high" or "low" viral load, rather than exact levels. Generally, the cut off for high and low viral load is approximately 800,000 IU/mL. Quantitative tests are less sensitive than qualitative tests but even so they can detect as few as 500 copies of the virus.

Branched chain DNA (bDNA)
Branched chain DNA tests are also quantitative and are based on the amplification of the detection signal, rather than the nucleic acid itself. This test is less prone to contamination and is more accurate when measuring higher levels of the virus, as compared to other quantitative tests. However, the bDNA assay is not as sensitive and is unable to measure levels of virus below 200,000 copies/ml.

Total HCV Core Antigen (Ag)
Total HCV Core Antigen test is a newer ELISA method for detection of HCV core protein. The HCV Core Ag appears to correlate well with HCV RNA findings to assess viremia in chronic hepatitis C. It is capable of both quantitative and qualitative determinations. It has a faster laboratory turn around time than other tests, is easy to use and is relatively inexpensive.