Hepatitis C (cont.)

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How is hepatitis C diagnosed?

There are several diagnostic tests currently are available for the diagnosis of hepatitis C infection. They can be categorized according to the way the tests are used.

Screening tests are tests that are used to diagnose a condition or disease among individuals not known to have the disease. They are particularly useful for individuals who have risk factors for the condition or disease.

The first step in screening for hepatitis C infection is to test blood for the antibody to hepatitis C using an enzyme mmuno-assays (EIAs). If the EIA test is negative (does not find the antibody), the patient is assumed to be free of hepatitis C. It takes several weeks (up to six months) for antibodies to develop after the initial infection with hepatitis C, so this screening test may miss a few newly-infected individuals. The EIA screening tests are very good (specific); if the test is positive the probability of having hepatitis C infection is greater than 99%.

Recombinant immunoblot assay (RIBA) is used to confirm the positive results of EIAs since occasionally a positive EIA is a false positive, that is, the test is positive when Hepatitis C is not present. Although the direct detection of HCV RNA (HCV PCR) also is widely used to confirm the HCV infection, RIBA still is useful to differentiate false positive results in the few individuals whose immune systems have eliminated the virus but still have antibodies left over from the resolved infection.

As previously described, HCV contains RNA. Several tests (assays) are available to measure the amount of HCV RNA in a person's blood. These tests are referred to as molecular tests because they examine the virus at the molecular level. A single negative test for RNA does not mean that there is no infection because the virus may appear in the blood intermittently or may exist in small amounts. Newer tests have helped by detecting smaller and smaller amounts of virus in the blood.

Testing for RNA is useful in determining whether or not a patient has circulating virus in the blood (viremia). Hence, it can be used to confirm that a positive EIA/ELISA truly reflects active HCV infection.

RNA testing also should be done in individuals who may have been recently exposed to hepatitis C. HCV RNA testing is more sensitive (that is, will detect more cases) than the conventional EIA testing in this setting. The reason for this greater sensitivity is that it may take a person several weeks after exposure to hep C to develop the antibodies that give rise to a positive EIA, whereas HCV RNA becomes detectable one to three weeks after exposure. Finally, HCV RNA testing may be helpful to assess a patient's response to treatment at certain time points during antiviral therapy (see treatment of hepatitis C below).

Currently, an anti-hepatitis C test is recommended as a hepatitis C screening test, and if the result is positive, current infection should be confirmed by a sensitive HCV RNA test. HCV RNA testing also should be done before starting any therapy. If a person is negative on screening test, no further testing is required, but if exposure to hepatitis C persists (for example, drug users) the test should be repeat at regular interval (i.e., annually). Patients whose immune systems are suppressed, including patients with HIV infection, should have HCV RNA testing to exclude hepatitis C infection. Blood tests also have been developed to identify subtypes of HCV, referred to as genotypes. This information is used to help guide treatment since genotypes respond differently to treatment. Genotype identification is recommended prior to initiation of treatment to guide selection of the most appropriate antiviral regimen.

The table below provides guidelines for interpreting the results of testing for HCV antibodies by EIA and RIBA and for hepatitis C virus RNA. These are standard interpretations, but it is important to remember that the diagnosis of hepatitis C infection should be made by an experienced clinician who is familiar with the patient's medical history.

Anti-HCV (ELISA/EIA) Anti-HCV (RIBA) HCV RNA Interpretation
Negative Negative Negative No infection
Positive Positive Positive Ongoing infection
Positive Positive Negative Past or current infection. Additional or repeat testing should be done to exclude fluctuating or low levels of virus.
Positive Negative Negative False positive ELISA; no infection
Positive Indeterminate Negative Situation unclear, consider additional testing
Negative Negative Positive New (acute) hepatitis C infection or chronic hepatitis C infection in an immunocompromised person unable to make adequate antibodies.

What about liver biopsy in the diagnosis of chronic hepatitis C?

Blood tests can tell the clinician whether hepatitis C is present but cannot tell the level of liver damage that has occurred. Liver biopsy allows the clinician to determine how much inflammation and scarring is present by examining a small sample of liver tissue. Liver biopsy gives information useful in the decision to initiate therapy. Significant liver damage is a risk factor for other conditions such as hepatocellular carcinoma and esophageal varices. Liver biopsy may be recommended when the clinician is uncertain about whether to begin treatment or wishes to monitor the response within the liver to therapy.

It is possible to measure liver stiffness with transient elastography, a safe non-invasive test. Stiffer livers mean that advanced liver fibrosis or cirrhosis may be present; however such tests do not completely replace the need for liver biopsy in routine clinical practice.

Several batteries of blood tests also have been found to be useful in diagnosing cirrhosis; however, like transient elastography, these tests have not completely replaced the need for liver biopsy.

Medically Reviewed by a Doctor on 5/26/2015

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