How do you find out if someone has hepatitis?

All types of hepatitis are diagnosed with a blood test.The hepatitis virus panel is a series of blood tests used to detect current or past infection by hepatitis A, hepatitis B, or hepatitis C. It can screen blood samples for more than one kind of hepatitis virus at the same time.Antibody and antigen tests can detect each of the different hepatitis viruses.Note: Hepatitis D only causes disease in people who also have hepatitis B. It is not routinely checked on a hepatitis antibody panel.

http://www.std-gov.org/stds/hepatitis.htm

http://www.nlm.nih.gov/medlineplus/ency/article/003558.htm