Note--Elevations of transaminases (ALT, aka "SGPT" and AST, aka "SGOP") are generally indicative of hepatocellular injury.  Active liver disease may be present histologically with normal transaminases.  The following table describes some causes of elevations of ALT and AST and diagnostic tests for those conditions:

Alcohol abuse Hx, GGT, MCV
Other hepatotoxins Hx, acetaminophen level (if acute)
Hemochromatosis Fe/TIBC, ferritin, genetic screening for the C282Y gene
Wilson's Disease Ceruloplasmin, urine copper excretion (elevations < 3x normal are nonspecific for Wilson's); liver Bx for copper quantitation; genetic screening
Viral Hepatitis HBSAg, Hep C Ab, CMV serology; if acute, IgM for hepatitis A
Autoimmune Hepatitis ANA for screening; anti-smooth muscle antibody, C3, C4, SPEP to help support the dx; if suspect that because of advanced disease the autoantibodies are waning, consider HLA typing for haplotypes B8 Dr3 or 4
Ischemic liver damage n/a
Biliary tract obstruction Alkaline phosphatase, imaging (u/s, ERCP, percutaneous transhepatic cholangiography)
Non-alcoholic steatohepatitis Imaging (u/s); liver bx
Primary Biliary Cirrhosis Anti-mitochondrial antibody
Primary sclerosing cholangitis Antineutrophil cytoplasmic antibodies
Autoimmune cholangitis ANA
Tuberculosis Chest x-ray
Sarcoidosis Chest x-ray
Other Liver biopsy (see below)

Other notes:

(Sources include Minuk GY. Canadian Association of Gastroenterology Practice Guidelines: evaluation of abnormal liver enzyme tests. Canadian Journal of Gastroenterology. 12(6):417-21, 1998 Sep.)