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Labs determine 'normal range' by surveying the people using that lab. For my lab, normal ALT is 6-34 and normal AST is 9-34. ALT is made in the liver so high levels indicate it is being leaked out of damaged liver cells into the bloodstream.
The ALT test measures the level of ALT in your blood. Consistently high levels of ALT in your blood can be a sign of liver damage. Aspartate Transaminase (AST) is an enzyme found in large amounts in your liver and other parts of your body. The AST test measures the level of AST in your blood.