ALT, AST, and Bilirubin
ALT (alanine aminotransferase) is an enzyme primarily located in liver cells. It participates in amino acid metabolism and is released into the blood when liver cells are damaged. Elevated ALT levels most often indicate inflammation or liver injury caused by hepatitis, toxic exposure, alcohol, medications, or other diseases.
AST (aspartate aminotransferase) is an enzyme found in the liver, heart, muscles, and other organs. Elevated AST may be associated not only with liver damage but also with heart diseases (e.g., myocardial infarction), muscle injuries, and other conditions. The AST to ALT ratio helps determine the nature of liver damage.
Bilirubin is a breakdown product of hemoglobin from red blood cells. It exists in two forms: direct (conjugated) and indirect (unconjugated). Elevated bilirubin causes jaundice (yellowing of skin and mucous membranes) and often indicates liver or bile duct dysfunction or increased red blood cell destruction (hemolysis).
Why ALT, AST, and bilirubin tests are performed:
- Assess liver function and detect liver damage
- Diagnose hepatitis, cirrhosis, fatty liver disease, and other liver conditions
- Determine causes of jaundice
- Monitor treatment effectiveness for liver diseases
How the test is performed:
- Blood is drawn from a vein fasting
- Avoid alcohol, fatty foods, and intense physical activity before the test
Important to know:
- ALT and AST levels together with bilirubin provide a comprehensive picture of liver status
- The AST to ALT ratio helps differentiate types of liver damage
- Additional tests (liver ultrasound, biopsy) may be required for accurate diagnosis