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* Context.--Disease guidelines specify universal alanine aminotransferase (ALT) thresholds for clinical decision-making, yet the effect of variability among ALT analyzers remains unclear. Objective.--To compare ALT results from different analyzers from 2012-2017. Design.--Veterans Health Administration (VHA) laboratories perform external ALT proficiency testing using standardized College of American Pathologists (CAP) samples in analyzers by 5 manufacturers. In this operational analysis, we evaluated 22 950 ALT values from 80 independent CAP samples tested at 223 laboratories. Using mixed effects modeling, we estimated the association between analyzer manufacturer and CAP outcome, adjusting for manufacturer, facility, and calendar year. We performed subgroup analyses on CAP samples with overall means near clinical guideline-specified thresholds, including less than 50 U/L (n = 10) and less than 35 U/L (n = 5). Results.--The VHA used Abbott Laboratories (n = 3175; 14%), Beckman Coulter Diagnostics (n = 8723; 38%), Roche Diagnostics (n = 2595; 11%), Siemens Healthineers USA (n = 5713; 25%), and Vitros/Ortho Clinical Diagnostics (n = 2744; 12%) analyzers. The CAP samples (n = 80 samples, n = 22 950 tests) covered a wide range of mean ALT values (21-268 U/L). The average difference in mean ALT value per sample between the highest-reading and lowest-reading manufacturers was 15.4 U/L (SD = 1.8) for the 10 samples with mean ALT less than 50 U/L, and it was 10.4 U/L (SD = 3.6) overall (n = 80). In linear mixed effects modeling, we found statistically significant differences in ALT values between the different manufacturers in each year. Conclusions.--We found statistically and clinically meaningful differences between analyzers across the ALT spectrum in each year, including at ALT levels lower than 50 U/L and lower than 35 U/L. Universal ALT thresholds should be avoided as a trigger for clinical action until differences between analyzers can be resolved. (Arch Pathol Lab Med. 2020;144:748-754; doi: 10.5858/arpa.2018-0622-0A), Alanine aminotransferase (ALT) is a marker of hepatocyte injury widely used to screen for and monitor liver disease. (1,2) Alanine aminotransferase features prominently in clinical algorithms for detecting and managing [...]

The article presents comments on a study on alanine aminotransferase (ALT) assay performance from various instrument manufacturers. Topics covered include the College of American Pathologists proficiency testing (CAP PT) samples' non-commutability with true human samples, and its possible results of patient misclassification and unnecessary treatment. Also noted is the reply that ALT thresholds should be avoided for clinical action unless materials are standardized.