Abnormal liver biochemical and function tests are frequently detected in asymptomatic patients since many screening blood test panels routinely include them . A population-based survey in the United States conducted between 1999 and 2002 estimated that an abnormal alanine aminotransferase (ALT) was present in 8.9 percent of respondents. Although the term "liver function tests" (LFTs) is used commonly, it is imprecise since many of the tests reflecting the health of the liver are not direct measures of its function. Furthermore, the commonly used liver biochemical tests may be abnormal even in patients with a healthy liver. However, for the sake of simplicity, the abbreviation "LFTs" will be used in this discussion to denote liver biochemical and function tests in general.
This topic review will provide an overview on the evaluation of patients with abnormal liver biochemical and function tests. Detailed discussions of the individual tests are presented separately. (See "Liver biochemical tests that detect injury to hepatocytes" and "Enzymatic measures of cholestasis (eg, alkaline phosphatase, 5’-nucleotidase, gamma-glutamyl transpeptidase)" and "Classification and causes of jaundice or asymptomatic hyperbilirubinemia" and "Tests of the liver's biosynthetic capacity (eg, albumin, coagulation factors, prothrombin time)".)
COMMON LIVER BIOCHEMICAL AND FUNCTION TESTS
Blood tests commonly obtained to evaluate the health of the liver include liver enzyme levels, tests of hepatic synthetic function, and the serum bilirubin level. Elevations of liver enzymes often reflect damage to the liver or biliary obstruction, whereas an abnormal serum albumin or prothrombin time may be seen in the setting of impaired hepatic synthetic function. The serum bilirubin in part measures the liver's ability to detoxify metabolites and transport organic anions into bile.
Liver enzymes — Liver enzymes that are measured in the serum include:
●Serum aminotransferases: alanine aminotransferase (ALT, formerly called SGPT) and aspartate aminotransferase (AST, formerly called SGOT)