Don't get too freaked out yet. Do you have any other symptoms, like nausea, jaundice (yellowing of the whites of your eyes, dark urine...), fatigue? Have you been taking any medication even antibiotics? Any herbal remedies? Many things can cause your ALT/AST to be elevated. How high are your numbers?
I have autoimmune hepatitis. It isn't caused by a virus, it's an autoimmune disorder. There are many disorders that affect the liver. Even gall bladder issues will cause your LFT's (liver function tests) to be elevated. Mono (EBV-Epstein Barr Virus) can cause it as well as CMV (cytomegalovirus) which usually causes flu-like symptoms...and sometimes, no symptoms at all.
Your doc should be running the viral serologies to rule out a viral type of hepatitis. Once those are done they should check for other viruses as the ones stated above (there are so many tests they can run to rule things out). And of course, repeat your regular labs. Doing a CT scan is great too.
Please let us know more and ask more questions if needed...question your doctor too. You are your own advocate.
Diagnosed with AIH January 2007,
CMV (cytomegalovirus) June 2008
meds: Azathioprine 100mg