There is an enormous amount of detailed information available on the different forms of viral hepatitis. Rather than re-invent the wheel, we've located some excellent primary source material from the Centers for Disease Control.
If you just want the basics, read below - otherwise, click here for excellent Overviews of Hepatitis A, B, C, D, and E.
Hepatitis A - Transmitted by fecal-oral route. Effective immunization available. Acute presentation, usually diarrhea and jaundice. Much of the world's population has had this disease at one time or another, and it resolves without sequellae in immunocompetent people. To test for it, simply order a Hep A test. The assay looks for Hep A antibody, particularly for the IgG or IgM components. If it finds either of them, the lab automatically quantitates for IgM to check for acute infection.
Hepatitis B - Transmitted by blood- or fluid- borne routes. Effective immunization available. 90% of patients present either acutely or asymptomatically. The acute presentation resolves, usually without sequellae. 10% of patients develop "chronic" Hep B, which is basically and Hep B that lasts over 6 months. It tends to lead to chronic hepatitis and cirrhosis.
The two parts of the virus that we most frequently look for in working up Hep B are the S (Surface), and C (Core).
Surface Antigen (S Ag) rises and falls, usually within a month. If it is present, it indicates an active infection with replicating virus.
Surface Antibody (S Ab) rises and falls over the course of about 10 years. The presence of S Ab indicates that the virus has been cleared, and that the patient is immune from Hep B (the protective antibody is what allows the vaccine to be effective). So, either S Ag is elevated or S Ab is elevated.
Occasionally, both the antigen and the antibody test positive. This indicates that the patient was tested during the following very small window:
Core antibody rises during infection and remains detectable for life. It is used to detect someone who has been infected with the virus, and not just immunized from it (which would give a positive S Ab).
There is an unusual condition in which a person has a positive core but negative S Ab. It indicates either that the infection occured over 10 years ago and the S Ab has worn off, or that the period of active infection is just ending, and the patient is in the period known as "core window," which looks like this:
Finally, you can order Hep B DNA, but it's not done regularly here, and doesn't add much to the workup of a typical Hep B.
Hepatitis C - Transmitted by blood- or fluid- borne routes. No immunization currently available - primarily due to the virus' rapid rate of mutation. The most common cause of viral hepatitis, and the #1 cause of liver transplants. The blood test to detect the virus was only developed in 1992, so anyone who received blood transfusions prior to 1992 should be tested, even if they have normal LFT's (the intensity of the disease waxes and wanes, and normal LFT's are possible in infected patients with temporarily inactive virus).
The current treatment of choice is Interferon, which has side effects that are intolerable to many patients. Only ~50% of patients respond to Interferon at all, and of those, only 50% have a prolonged response.
The screening method currently in use is to look for the Hep C antibody, which is not protective. If the test is negative, there is no disease. If it is positive, one of three possibilities exist:
To rule out false positives, you can run a test called RIBA.
To confirm viremia, the best test is PCR - if negative, repeat in 6 months to cover for possible troughs in viral load.
Hepatitis D - Only occurs in patients with Hep B - it uses the Hep B machinery to replicate itself. If chronic hepatitis occurs with Hep D, it is much more likely to lead to liver destruction than with simple Hep B (70-80%, compared to ~10%).
Hepatitis E - Transmitted by fecal/oral route. Very uncommon in US except in people traveling to endemic areas. Acute presentation (abdominal pain anorexia, dark urine, fever, hepatomegaly, jaundice, malaise, nausea, and vomiting), but no documented chronic disease.