We developed field methods without sample blank reactions to estimate the reference methods proposed by the Japan Society of Clinical Chemistry (JSCC methods) for the measurement of aspartate (AST) and alanine (ALT) aminotransferase activities in human sera. In our methods, activities were measured at 30°C but there were no dicrepancies between the activites at 30°C and 37°C. Conversion factors from 37°C to 30°C were obtained as 1/1.49 and 1/1.45 for AST and ALT respectively. AST and ALT activities by our methods were so well correlated to those of the JSCC methods that clinical evaluations of the JSCC methods were made possible by our methods. AST and ALT activities by our methods were also well correlated to those of the conventional Reitman-Frankel's and Karmen's methods in all the patient sera. Conversion factor of AST/ALT ratios by the conventional methods to the present methods was about 0.7 in healthy subjects and also in the patients with various liver diseases, however, correlation between AST and JALT activities were different and specific in these groups. Therefore, even in the sera including mitochondrial AST, AST and ALT activities and AST/ALT ratios by JSCC methods were easily converted to those of the conventional methods by the respective conversion factors.
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