A simple blood test can detect antibodies to hepatitis C virus in your blood (antibodies are proteins made by the immune sytem to attack the virus, bacteria ect.) A positive test means that you may at some stadge been infected with hepatitis C.
However, this test remains positive even in people who have cleared the virus from their body. (The antibodies remain even if the virus has gone.) Also, it can take up to six months for the antibody test to become positive after first being infected, as the body may take a while to make these antibodies. So, a negative test does not necessarily rule out a recently acquired infection. A repeat test in a few months may be advised in some people who have recently been at risk of catching hepatitis C.
If the antibody test is positive, then a further blood test is needed to see if the virus is still present. This is called a PCR test. This is a more specialized test which detects particles of the virus. Tests may also be done to find exactly which type of hepatitis C virus you are infected with.