The potential of reducing AST testing in hospital settings

Aspartate aminotransferase (AST) is regularly ordered with alanine aminotransferase (ALT) to assess liver integrity. In many situations, AST testing provides little or no added clinical value, since ALT is more specific and the both enzyme activities highly correlate. The objective of this study is to determine the potential reduction in AST testing, if not performed when ALT results are within reference intervals (RI).

Results for patients >18 years of age for both AST and ALT from the same specimen were obtained for the period January 1, 2017 - December 31, 2017. We calculated frequency of AST and ALT results that had various combinations of results within and above the RI. We also investigated the clinical locations of origin for the samples.

In total 87,704 paired samples with both AST and ALT test results were recovered. The total of 73.2% of AST tests for males and 66.9% for females would be eliminated if we performed AST testing only when ALT was increased. However, 7.4% of elevated AST tests would be missed for males and 3.8% for females due to ALT being within limits. Specifically in the outpatient clinics, 79% male and 73% females paired enzyme results were within RI. Only 4% of males and 3% of females had paired results where ALT was within RI while AST > RI.

The rate of test results with increased AST while ALT is within the RI is low enough to recommend limiting AST testing only to cases where ALT is above the RI. Our recommendation for AST restriction is to begin with the hospitals outpatient clinics.