Liver Disease

Laboratory Tests And Diagnostic Procedures in Hepatobiliary Disease

Patricia Liu, M.D.
Liver function tests are best utilized in concert with the clinical situation and in conjunction with serial determinations to ascertain the cause or evolution of the hepatic disorder. In addition, stool and urine tests, radionuclide imaging, contrast cholangiography (transhepatic cholangiography and endoscopic retrograde cholangiopancreatography), and histological assessment (liver biopsy) are often utilized to delineate the nature of the liver disease.

Serum Enzymes (Serum Aminotransferase Transaminases)
Serum glutamic oxaloacetic transaminase, also referred to as aspartate aminotransferase, and serum glutamic pyruvic transaminase, also called alanine aminotransferase (AST and ALT) are commonly employed to ascertain liver function. Striking elevations in the serum levels of these two enzymes are encountered in acute viral hepatitis, acute drug- or toxin-induced liver damage, and ischemic hepatitis. In addition, levels exceeding 500 IU/L and, on rare occasions, 1,000 IU/L can also be seen in patients with severe chronic active hepatitis, transiently in patients with common bile duct stones, and in patients with Budd-Chiari and veno-occlusive disease.
There are a number of important hepatic disorders in which the serum AST and ALT are normal or minimally elevated . These include idiopathic genetic hemochromatosis, methotrexate-induced liver injury, liver dysfunction due to amiodarone, the liver disease associated with jejunal ileal bypass surgery, and patients with chronic hepatitis C virus infection.
The ratio of AST and ALT is also sometimes of value in clinical practice. A ratio greater than 2 with both AST and ALT being less than 300 IU/L is characteristic of alcoholic liver disease.
On rare occasions, if both the AST and ALT are elevated, patients are subjected to a liver biopsy after a very thorough serologic workup only to find that the liver histology is completely normal. It is very important to exclude a primary muscle disorder in such patients since not only the AST but also the ALT can be elevated in patients with muscle disorders.

Serum Alkaline Phosphatase
The sources of serum alkaline phosphatase include liver, bone, small intestine, placenta, and, on rare occasions, tumors capable of producing alkaline phosphatase.
In general, patients with cholestasis have increased levels. However, the level of serum alkaline phosphatase is not helpful in distinguishing intrahepatic from extrahepatic cholestasis. Rarely, patients with hypernephroma and Hodgkin's disease have elevated levels in the absence of liver involvement. Also, patients with Wilson's disease often have normal values.
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