Limiting the testing of AST: a diagnostically nonspecific enzyme.

OBJECTIVES: Annually, millions of pairs of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) tests are ordered. These enzymes are highly correlated, and ALT is far more specific diagnostically than AST. To reduce AST testing, we suggest measuring AST only when ALT exceeds a predetermined limit.
METHODS: We derived the proportions of elevated ASTs that would not be measured based on 15 months of paired inpatient and outpatient ALT and AST data.
RESULTS: For inpatients, a 35 U/L ALT limit for initiating AST testing would reduce AST testing by 51%, missing only 3% and 7.5% of ASTs exceeding 50 U/L and 35 U/L, respectively. In outpatients, AST testing can be reduced by more than 65%, with fewer missed elevated ASTs (0.5% and 2% of the ASTs exceeding 50 U/L and 35 U/L, respectively).
CONCLUSIONS: Conservatively, $100 million could be saved annually in the US health care budget by selectively limiting AST testing in just the US outpatient environment. Copyright© by the American Society for Clinical Pathology.