Approach to the patient with abnormal liver biochemical and function tests
- Lawrence S Friedman, MD
Lawrence S Friedman, MD
- Section Editor — General Gastroenterology
- Professor of Medicine
- Harvard Medical School
- Tufts University School of Medicine
- Section Editor
- Sanjiv Chopra, MD, MACP
Sanjiv Chopra, MD, MACP
- Editor-in-Chief — Gastroenterology/Hepatology
- Section Editor — General Hepatology
- Section Editor — Gallbladder and Biliary Tract Disease
- Professor of Medicine
- Harvard Medical School
- Senior Consultant in Hepatology
- James Tullis Firm Chief
- Beth Israel Deaconess Medical Center
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 commonly measured in the serum include:
●Serum aminotransferases: alanine aminotransferase (ALT, formerly called SGPT) and aspartate aminotransferase (AST, formerly called SGOT)
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- COMMON LIVER BIOCHEMICAL AND FUNCTION TESTS
- Liver enzymes
- - Aminotransferases
- - Alkaline phosphatase
- - Gamma-glutamyl transpeptidase
- - 5'-nucleotidase
- - Lactate dehydrogenase
- Function tests
- Reference ranges
- INITIAL EVALUATION
- Physical examination
- Laboratory tests
- - Patterns of LFT abnormalities
- - AST to ALT ratio
- - Magnitude of AST and ALT elevations
- - Other laboratory abnormalities
- ELEVATED SERUM AMINOTRANSFERASES
- Acute liver failure
- Marked elevation without liver failure
- - Differential diagnosis
- - Evaluation of markedly elevated aminotransferases
- Mild to moderate elevation
- - Differential diagnosis
- - Evaluation of mildly or moderately elevated aminotransferases
- ELEVATED ALKALINE PHOSPHATASE
- Confirming an elevated alkaline phosphatase is of hepatic origin
- Differential diagnosis
- Evaluation of elevated alkaline phosphatase
- - Extrahepatic cholestasis
- - Intrahepatic cholestasis
- ISOLATED GAMMA-GLUTAMYL TRANSPEPTIDASE (GGT) ELEVATION
- ISOLATED HYPERBILIRUBINEMIA
- Unconjugated (indirect) hyperbilirubinemia
- - Hemolysis
- - Impaired hepatic uptake or conjugation
- Conjugated (direct) hyperbilirubinemia
- ISOLATED ABNORMALITIES OF TESTS OF SYNTHETIC FUNCTION
- WHEN TO REFER TO A SPECIALIST
- INFORMATION FOR PATIENTS
- SUMMARY AND RECOMMENDATIONS