Liver function tests: What do they involve?

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Liver function tests: What do they involve?

Question

I recently started a new medication, and my doctor has recommended regular testing of my liver function. What does that involve?

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Answer

Liver function tests are used to detect, evaluate and monitor liver disease or damage. A doctor may recommend liver function tests if you:

  • Have a high risk of liver disease
  • Take medication that may cause liver damage
  • Have signs and symptoms of liver disease

Liver function tests generally refer to blood tests that evaluate the presence of liver damage or disease. These tests usually can be done on a single blood sample and may include:

  • Alanine transaminase (ALT). An enzyme found mainly in liver cells, ALT helps your body metabolize protein. Normally, ALT levels in the blood are low. When the liver is damaged, ALT is released in the bloodstream.
  • Aspartate transaminase (AST). The enzyme AST plays a role in the metabolism of alanine, an amino acid. AST is found in high concentrations in liver cells. An increase in AST levels may indicate liver damage or disease.
  • Alkaline phosphatase (ALP). ALP is an enzyme found in high concentrations in the liver and bile ducts, as well as some other tissues. Higher than normal levels of ALP may indicate liver damage or disease.
  • Albumin and total protein. Levels of albumin — a protein made by the liver — and total protein show how well your liver is making proteins that your body needs to fight infections and perform other functions. Lower than normal levels may indicate liver damage or disease.
  • Bilirubin. Bilirubin results from the breakdown of red blood cells. Normally, bilirubin passes through the liver and is excreted in your stool. Elevated levels of bilirubin (jaundice) may indicate liver damage or disease.

Additional tests that may be used to evaluate liver function include:

  • Gamma-glutamyl transferase (GGT). This test measures the amount of the enzyme GGT in the blood. Higher than normal levels may indicate liver or bile duct injury.
  • Lactate dehydrogenase (LDH). LDH is an enzyme found in many body tissues, including the liver. Elevated levels of LDH may indicate liver damage.
  • Prothrombin time (PT). This test measures the clotting time of plasma. Increased PT may indicate liver damage.

Last Updated: 07/18/2006
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