A systematic review of data on biological variation for alanine aminotransferase, aspartate aminotransferase and γ-glutamyl transferase

Background: Alanine aminotransferase (ALT), aspartate aminotransferase (AST) and gamma-glutamyl transferase (GGT) are enzymes measured in serum or plasma to investigate liver disease. The aim of this work is to assess the validity of published biological variation (BV) data currently available for these enzymes. Methods: Publications containing BV data for ALT, AST and GGT were identified by searching PubMed using the following keywords: biological varia(star), RCV, CVw, CVi, CVb, and CVg. The 95% confidence intervals for the within- and between-subject coefficients of variation were calculated using the analytical imprecision, the number of subjects, samples and replicates. Results: The searches identified 10 publications with ALT, 14 with AST and nine with GGT data. The protocols presented in those publications as used were varied. The ranges of within-subject variation reported were: ALT: 11.1%-58.1%, AST: 3.0%-32.3% and for GGT: 3.9%-14.5%. The median values (ALT: 18.0%, AST: 11.9% and GGT: 13.8%) were similar to those listed in a BV database commonly used as a reference source. Conclusions: Published BV data for ALT, AST and GGT demonstrate a wide range of values derived from inconsistent protocols. The quality of the presentations of the data is variable. These findings raise concerns around the utility of the data currently available and highlight the need for critical appraisal of such publications. The working group on BV of the European Federation of Clinical Chemistry and Laboratory Medicine is undertaking work to develop a critical appraisal checklist for the production and publication of reliable BV data.