What Does ALT Stand For in Laboratory Testing?
ALT stands for Alanine Aminotransferase (also called alanine transaminase), which is an enzyme primarily concentrated in the liver that serves as a highly specific marker for hepatocellular injury. 1
Definition and Function
- ALT is an enzyme that catalyzes the transfer of amino groups from alanine to ketoglutaric acid 2
- It normally resides in serum and body tissues, especially in the liver, and is released into the serum as a result of tissue injury 3
- ALT is more specific for liver injury than AST (aspartate aminotransferase) because it is primarily concentrated in liver tissue with minimal presence in cardiac muscle, skeletal muscle, kidneys, and red blood cells 1, 4
Clinical Significance
- ALT is the most liver-specific aminotransferase available and serves as an established marker of liver diseases 1, 2
- It is commonly used in clinical practice as both a screening and diagnostic test for liver diseases 5
- ALT has been shown to be a good predictor of liver-related and all-cause mortality 5
- The concentration of ALT in serum may be increased with acute damage to hepatic cells 3
Normal Reference Ranges
- Normal ALT ranges differ significantly by sex: 29-33 IU/L for males and 19-25 IU/L for females 1
- These sex-specific ranges are considerably lower than many commercial laboratory cutoffs 1
ALT Isoforms
- Two isoforms exist: ALT1 and ALT2, which have identical enzymatic capacities 6
- ALT1 is predominantly found in liver tissue, while ALT2 is more abundant in skeletal muscle 6
- During liver damage, ALT1 activity leakage into plasma greatly exceeds that of ALT2, and measurement of ALT1 equals total ALT activity 6
- During skeletal muscle injury, ALT2 leakage exceeds ALT1, allowing differentiation between hepatic and extrahepatic injury 6