Diagnosing hepatitis C is done by testing a blood sample.¹

Antibodies against the hepatitis C virus (HCV) can usually be detected in the blood about six to nine weeks after infection, although some people may take up to six months to develop antibodies. This delay is sometimes called the ’window period’.

Antibodies are not part of the virus; rather they are created by the immune system as an immune response. A positive test result only indicates that the person has had contact with the virus. It is not possible to distinguish between an acute, chronic or cured hepatitis C infection with an antibody test. If HCV antibodies are detectable, the next diagnostic step takes place.

If the virus is still active – a hepatitis C infection is currently present – it is not only antibodies which are detectable in the blood, but also the genetic material of the virus (HCV RNA). If HCV antibodies are detected, then a very sensitive test with what is known as PCR (polymerase chain reaction) is used: a positive test result means that the virus is circulating in the bloodstream at the time of the test.

If HCV RNA is detected in the blood, a hepatitis C infection is present.

No antibodies can be detected if infection has occurred recently. For people with immune deficiencies (e.g. HIV/AIDS), antibodies may take up to nine months to develop. Some people with severe immune deficiency may never develop antibodies, even if HCV RNA is detectable.

In contrast, newborn babies whose mothers have hepatitis C can have HCV antibodies in their blood without having the infection.

Where recent infection is suspected, an HCV RNA test is carried out at once independently of the antibody test. This test is more time-consuming and expensive than the antibody test, but it generally produces reliable results as early as two weeks after an infection.

Many people do not seek out a test for HCV. Often, people with hepatitis C are diagnosed as a result of other investigations which detect changes in liver function. A blood count may be carried out due to health problems, or perhaps as part of a routine check-up. Signs of liver inflammation can be found in blood with an HCV infection. Certain substances are released into the blood by the destruction of the liver cells, which can then be detected in unusually high concentrations in the blood. Two important liver enzyme values, which are often checked in routine blood tests, are the transaminases AST (aspartate aminotransferase) and ALT (alanine aminotransferase).