Alanine Aminotransferase (ALT) - This test is crucial for diagnosing and managing liver conditions such as viral hepatitis and cirrhosis. ALT is an enzyme found mainly in the liver, and its levels are usually much lower in other tissues compared to the liver. High ALT levels typically indicate liver disease. This test is often done alongside the AST test to pinpoint the source of liver issues and to differentiate between liver and heart diseases.