Aspartate and alanine aminotransferases are two of the enzymes most frequently measured by the clinical laboratory. They are most commonly used in the differential diagnosis of various liver diseases where the ratio of the two enzymes provides additional clinical insight. AST is also useful in many cases for diagnosis, or estimating severity, of myocardial infarction. The mitochondrial isoenzyme of AST has a growing significance in the diagnosis of alcoholism and other conditions.