From the Guidelines
Aminotransferases tests, including aspartate aminotransferase (AST) and alanine aminotransferase (ALT), and the alkaline phosphatase (ALP) test, are crucial blood tests used to evaluate liver function and detect liver damage, with ALT being more specific to the liver and AST also found in heart and muscle tissue, as noted in the 2023 study by the American College of Radiology 1. The aminotransferases tests are used to assess hepatocellular damage, with normal ALT levels ranging from 29 to 33 IU/L in men and 19 to 25 IU/L in women, according to the study 1.
- The severity of abnormal aminotransferase levels can be classified as mild, moderate, or severe, based on the upper reference limit, with moderate and severe classifications having significant clinical overlap, as discussed in the study 1.
- ALT elevations are specific for liver injury due to low concentrations in skeletal muscle and kidney, whereas AST elevations can be caused by disorders involving the heart, skeletal muscle, kidneys, brain, and red blood cells, as mentioned in the study 1. The alkaline phosphatase (ALP) test is used to evaluate cholestatic liver disease, with pathologically increased levels indicating obstruction of biliary outflow or impairment in bilirubin uptake, as noted in the study 1.
- Elevated ALP levels without impairment of other liver enzymes suggest a cholestatic etiology, and if ALP is elevated in isolation, a suspicion of cholestatic disease is raised, as discussed in the study 1. In clinical practice, these tests are essential for detecting and monitoring liver damage, and their interpretation should always consider the patient's complete clinical picture, as emphasized in the 2023 study by the American College of Radiology 1.
From the Research
Aminotransferases (Liver Enzymes) Tests
- The aminotransferases tests, including aspartate aminotransferase (AST) and alanine aminotransferase (ALT), are used to assess liver injury or function 2, 3.
- These tests are commonly used to screen for liver disease, but interpretation of results can be complicated 2.
- The ratio of serum aspartate to alanine aminotransferase (AST/ALT) can be used as a clue to the etiology of the underlying liver disease, with a ratio greater than 2.0 often indicating alcoholic liver disease and a ratio less than 1.0 indicating chronic hepatitis or chronic cholestatic syndromes 4.
Alkaline Phosphatase (ALP) Test
- The alkaline phosphatase (ALP) test is used to assess liver function and diagnose liver dysfunction 3, 5.
- The high-molecular-mass ("biliary") isoenzyme of alkaline phosphatase is a highly sensitive index to cholestasis and can be used to diagnose liver dysfunction in certain conditions, such as cystic fibrosis 5.
Causes and Evaluation of Elevated Liver Enzymes
- Elevated liver enzyme levels, including AST and ALT, can be associated with significant underlying liver disease and increased risk of liver-related and all-cause mortality 6.
- Common causes of mildly elevated transaminase levels include metabolic dysfunction-associated steatotic liver disease (MASLD) and alcoholic liver disease, while uncommon causes include drug-induced liver injury, chronic hepatitis B and C, and hereditary hemochromatosis 6.
- Initial laboratory testing for elevated liver enzymes should include a complete blood cell count with platelets, blood glucose, lipid profile, hepatitis B surface antigen, hepatitis C antibody, serum albumin, iron, total iron-binding capacity, and ferritin 6.