How is it used?
Hepatitis C tests are used to detect and diagnose an infection and/or to monitor the treatment of hepatitis C virus (HCV). Tests are used to detect the condition if a person:
- Has been exposed to someone with HCV
- Participates in high risk behaviors such as injecting street drugs
- Has abnormal liver function tests
- Has symptoms associated with liver disease, such as jaundice, dark urine, nausea, or unexpected weight gain or loss
The following tests may be used to screen for and/or detect HCV:
- Anti-HCV test detects the presence of antibodies to the virus, indicating exposure to HCV. This test cannot distinguish between someone with an active or a previous HCV infection. Usually, the test is reported as “positive” or “negative.” There is some evidence that if the test is “weakly positive,” it may be a false positive. The Centers for Disease Control and Prevention (CDC) suggests that weakly positive tests be confirmed with the HCV RIBA test before being reported.
- HCV recombinant immunoblot assay (RIBA) test is an additional test ordered to confirm the presence of HCV antibodies. In most cases, it can tell if the positive anti-HCV test was due to exposure to HCV (positive RIBA) or represents a false signal (negative RIBA). In a few cases, the results cannot answer this question (indeterminate RIBA). Like the anti-HCV test, the RIBA test cannot distinguish between a current or past infection.
The following tests may be used to diagnose a current infection and to guide and monitor treatment:
- HCV RNA test, Qualitative may be used to distinguish between a current or past infection. It is reported as a “positive” or “detected” if any HCV viral RNA is found; otherwise, the report will be “negative” or not detected.” It may also be ordered after HCV treatment is complete to see if the virus has been eliminated from the blood. These tests are seldom used any more.
- HCV Viral Load (HCV RNA test, Quantitative) detects and measures the number of viral RNA particles in the blood. Viral load tests are often used before and during treatment to help determine response to treatment by comparing the amount of virus before and during treatment (usually at several time points in the first three months of treatment). Successful treatment causes a decrease of 99% or more (2 logs) in viral load soon after starting treatment (as early as 4-12 weeks) and usually leads to viral load being not detected even after treatment is completed. Some newer viral load tests can detect very low amounts of viral RNA.
- Viral genotyping is used to determine the kind, or genotype, of the HCV virus present. There are 6 major types of HCV; the most common (genotype 1) is less likely to respond to treatment than genotypes 2 or 3 and usually requires longer therapy (48 weeks versus 24 weeks for genotype 2 or 3). Genotyping is often ordered before treatment is started to give an idea of the likelihood of success and how long treatment may be needed.
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When is it ordered?
The CDC recommends screening for HCV infections in the following cases:
- If you have ever injected illegal drugs
- If you received a blood transfusion or organ transplant before July 1992*
- If you have received clotting factor concentrates produced before 1987
- If you were ever on long-term dialysis
- For children born to HCV-positive women
- For health care, emergency medicine, and public safety workers after needlesticks, sharps, or mucosal exposure to HCV-positive blood
- For people with evidence of chronic liver disease
*The blood supply has been monitored in the U.S. since 1992, and any units of blood that test positive for HCV are rejected for use in another person. The current risk of HCV infection from transfused blood is about 1 case per two million transfused units.
Most people newly infected with HCV have no symptoms or ones that are so mild that they rarely prompt a person to visit a doctor and get tested for HCV. However, about 10-20% of people may experience symptoms such as fatigue, pain in the abdominal area, decreased appetite, and jaundice and may be tested for HCV.
A positive anti-HCV test may be confirmed with an HCV RIBA test, especially when the anti-HCV test is “weakly positive.” Many physicians do not use RIBA since it still does not determine if a person is currently infected. Quantitative HCV-RNA is often ordered when the antibody test is positive to see if the infection is still present. HCV viral load and genotyping may be done when treatment is planned; viral load may be ordered periodically to monitor response to treatment and at the completion of treatment to evaluate its effectiveness.
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What does the test result mean?
Interpretation of the HCV tests is shown in the table below. In general, if the HCV antibody test is strongly positive, then someone has likely been infected at some time with hepatitis C. If the HCV RNA test is positive, then the person has a current infection. If no HCV viral particles are detected, then the person either does not have an active infection or the virus is present in very low numbers.
Is there anything else I should know?
HCV antibodies usually do not appear until several months into an infection but will always be present in the later stages of the disease.
About 25% of those with HIV/AIDS also have an HCV co-infection, and their liver disease is likely to progress at an accelerated rate.