What do liver function tests check?

A liver function test checks the enzyme and protein levels in the blood. Enzymes found in the liver and other parts of the body include alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), and gamma-glutamyl transpeptidase (GGT). High levels of these enzymes could mean damage to the liver or bile duct.

The liver also produces proteins, including albumin, globulin, and prothrombin. Low levels of these proteins could be a sign of liver damage. A prothrombin time test shows how long it takes for blood to clot.

A liver function test also measures platelet counts and glucose levels. (Platelets help the blood to clot in order to stop bleeding.)

The liver function test also measures bilirubin levels. Bilirubin is a fluid created from the breaking down of red blood cells. If the liver is damaged, bilirubin can leak out of the liver. This can cause the disease jaundice, in which the skin or eyes turn yellow. High bilirubin levels can also make urine darker in color.

What should I do to prepare for a liver function test?

Your healthcare provider may ask you not to eat, drink, or take certain medications in order to avoid affecting the test results.

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