It is true that a viral illness can transiently raise the ALT level. Repeating the test would be a reasonable option.
If the elevation persists, testing for hepatitis should be done (which you have already had). You can consider an abdominal ultrasound to image the liver and gallbladder.
Persistantly marked elevation of ALT may warrant a liver biopsy.
These options can be discussed with your personal physician.
Followup with your personal physician is essential.
This answer is not intended as and does not substitute for medical advice - the information presented is for patient education only. Please see your personal physician for further evaluation of your individual case.
Kevin, M.D.
http://www.straightfromthedoc.com