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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.
What Are the Normal AST and ALT Levels? The normal levels of AST and ALT vary from person to person and depend on your BMI, or the ratio of your height and weight. A small amount of AST and ALT is normally in your blood, so it's really a large increase over your normal level that indicates a problem.