There are two versions of the test, and these detect antibodies. Antibodies are produced by the body to protect itself from antigens (foreign proteins). IgM (immunoglobulin M) is the first antibody produced by the body when it is exposed to a virus and is used for early detection of infection. IgM antibodies to HAV are used in a patient with evidence of acute hepatitis, such as jaundice, dark urine, pale colored stools, fever, and loss of appetite. IgG (immunoglobulin G) antibodies develop later and remain present for many years, protecting the person against further infection by the same virus. A total antibody test (which detects both IgM and IgG antibodies) detects both current and previous infection with HAV and also will be positive after receiving the hepatitis A vaccine.

Testing for the presence of IgM antibodies to hepatitis A is done if you have the symptoms and/or are likely to have been exposed to the virus. If you have being considered for the HAV vaccine, a total antibody test may be ordered before you are given the vaccine to see if you need it (if the antibodies are already present, the vaccine won’t help you). Once you have completed the two doses of the vaccine, the total HAV antibody test can also be used to see if you have responded to the vaccine.

If the test result is positive (or reactive) and you have not gotten the HAV vaccine, you have had a hepatitis A infection – even if you were not aware of it. About 30% of adults over age 40 have antibodies to HAV. If you have been given the vaccine, a positive result means you are immune to HAV and cannot be infected by it.

It is presumed that one infection with hepatitis A produces lasting immunity against further infections.