PS the information above was quoted from:
http://www.labtestsonline.org/understanding/analytes/alt/test.html
Besides liver disease, which might be caused by, among other things, alcohol, obesity or Hepatitis, ALT levels might be raised also by strenuous exercise, a shot or injection of medicine into the muscle tissue.
Some drugs or natural supplements may also raise ALT levels.
I think you would be wise to check with your doctor.
Good luck!