Hepatitis A can be diagnosed using blood tests. Your health care provider can order these tests if you have symptoms of hepatitis A or if you want to know if you were infected with HAV in the past.
The blood test looks for two different types of antibodies to the virus. First it looks for immunoglobulin M (IgM) antibodies, which the immune system produces five to 10 days before symptoms appear and usually disappear within six months. It also looks for IgG antibodies, which replace IgM antibodies and protect against future HAV infection.
If the blood test shows that you are negative for both IgM and IgG antibodies, you probably have never been infected with the virus and should consider getting the HAV vaccine.
If you are positive for IgM antibodies and negative for IgG antibodies, HAV infection most likely took place within the past six months and is either in the process of being cleared by the immune system or getting worse.
If you are negative for IgM antibodies and positive for IgG antibodies, either you were infected with HAV at some time in the past or you have been vaccinated against hepatitis A; in either case, you are now immune to the virus.