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Liver Functions Tests

This test is abbreviated as "LFT" and applies to a variety of blood tests that provide a general indication of the condition of the liver and biliary system. Basically, these tests are used to diagnosed and/or monitor liver disease. They may be specific tests that can help diagnosed an underlying cause of hepatitis disease, truer indicators of general liver function (serum albumin, and prothrombin time) or they may simply be markers of disease (ALT, AST, alkaline phosphatase and GGT). Your doctor will include the interpretation of these tests in the context of your physical examination, other tests (X-rays or imaging studies), and medical history.

The two categories of liver enzymes (proteins inside of cells), alanine aminotransferase or ALT and aspartate aminotransferase or AST (formerly known as SGPT and SGOT), are indicators of liver cell damage. These tests are also used to monitor the course of chronic hepatitis and the response to certain treatments, such as interferon and prednisone. Other liver enzyme tests include alkaline phosphatase or Alk.Phos., and gammaglutamyltranspeptidase or GGT, which indicate obstruction to the biliary system within the liver or in the larger bile channels outside the liver.

When the liver cells are damaged, the ALT and AST enzymes filter out and end up in the body's circulatory system causing the blood level of these enzymes to rise. Due to the fact that the AST is usually elevated in diseases of other organs (e.g., heart, muscle), the ALT is a more specific indicator of liver inflammation. The elevation of these enzymes may be minimal (less than 3 times normal) or moderate (100-300 U/L) in chronic hepatitis or cirrhosis, while in severe liver injury, such as acute viral hepatitis, they may elevate to the high 100s or over 1,000 U/L. Yet, mild or moderate elevations are nonspecific and can be caused by a number of liver disease.

The GGT is employed as a supplementary test to be certain that the elevation of alkaline phosphatase is truly coming from the liver or the biliary tract. The reason for this is that alkaline phosphatase is also found in other organs (e.g. bone, intestine, placenta) and in diseases of these organs the GGT is not elevated. However, both the GGT and alk.phos. are elevated in a large number of disorders affecting bile drainage; for example, gallstones or tumors that block the common bile duct and drug-induced hepatitis or alcoholic liver disease that blocks the flow of bile in small channels within the liver. Medications or alcohol can often cause changes in liver cell enzymes which produces a mild or moderate elevation of GGT together with normal alk.phos. making interpretation difficult, but without damage to the liver.

The levels of bilirubin (main bile pigment) may be elevated in many diseases of the liver or biliary tract. Primarily formed due to the breakdown of heme (a substance in red blood cells), bilirubin is taken from the blood processed through the liver and is then secreted into the bile. This elevation produces jaundice, the yellow discoloration of the eyes and skin. Normal levels of bilirubin are less than 1.2 mg/dl. Jaundice is usually noticeable at levels high than 3 mg/dl. This interpretation is also nonspecific due to the fact that bilirubin levels may be elevated in a number of biliary tract or liver diseases. Serum bilirubin, in contrast, indicates the ability of the liver to take up, process and secrete bilirubin into the bile, and is considered a true LFT test.

Finally, physicians may order more specific tests to determine the cause of a liver disease. These are serologic or autoimmune tests which are usually not included in routine automated chemistry panels.

© Copyright 2000 - The Latino Organization for Liver Awareness