A blood test for antibodies to HCV will usually tell whether or not a person has been exposed to the virus. United Kingdom guidelines recommend that all HIV-positive patients be tested for HCV at least once, with subsequent tests for people at higher risk of HCV infection or with unexplained liver disease. Tests should also be performed to exclude co-infection with hepatitis B, and HIV-positive individuals should be vaccinated for both hepatitis A and B.
Some HIV-positive people with HCV may not produce enough antibodies to HCV, resulting in falsely negative HCV antibody tests.1 2 3 Thus, if hepatitis C is suspected in HIV-positive individuals with negative HCV antibody tests, a confirmatory HCV polymerase chain reaction (PCR) test may be necessary. A history of injection drug use, CD4 cell counts below 200 cells/mm3, or elevated ALT liver enzyme levels have been identified as the strongest predictors of falsely negative HCV antibody tests.
The HCV PCR test, like the HIV PCR, is a test that measures the amount of HCV genetic material (RNA) in the blood (i.e. the HCV viral load). An HCV viral load test can indicate whether someone is among the small percentage of people who clear HCV from the body naturally without treatment. Viral load testing is also used to monitor the effectiveness of treatment. Unlike HIV viral load, however, HCV viral load is not directly related to HCV disease progression. It also is not an indicator of when to commence treatment, but it does suggest how long treatment should last; people with high HCV viral loads (above 2 million copies/ml) may require a longer course of treatment.
Liver function tests include the liver enzymes alanine aminotransferase (ALT) and aspartate aminotransferase (AST), which often increase during liver inflammation. These tests may give an indication of whether HCV has caused liver damage, and can also help determine whether hepatitis C treatment is working or whether anti-HIV medications are harming the liver. But the tests are much less useful for HCV than for HBV, since some people have quite normal liver function tests even though they have sustained significant liver damage. In addition, liver enzyme levels may not reveal the full extent of liver disease in co-infected people, and test interpretation may be complicated in people taking antiretroviral drugs. For more on liver function tests, see Liver function in A to Z of tests.
In order to tell whether liver damage is present, a liver biopsy may be necessary. In biopsy, a small sample of liver tissue is extracted via a needle and examined under a microscope for signs of liver injury. Biopsy test results are typically reported in terms of fibrosis stage (F0 to F4). Liver biopsies can help to determine what the need for treatment. Repeat biopsies may be performed to check if liver disease is progressing. Usually repeat biopsies are recommended every three to five years, but because liver damage can progress more quickly in co-infected people, some experts think such individuals should receive repeat biopsies more frequently.
Until recently, it was thought that liver biopsy was the only way to accurately assess liver damage, but many researchers are developing non-invasive tests that assess liver damage indirectly via chemical markers in the blood (e.g., APRI, SHASTA).4 5 6 7 Another type of test called elastography (e.g., FibroScan, FibroTest) measures liver stiffness, which is highly correlated with fibrosis stage.8 Recent international guidelines support the use of non-invasive techniques as opposed to liver biopsy.9