Research on the comparability of AST results by improved reference method

Objective To research the comparability of aspartate aminotransferase(AST) results among different laboratories by a reference method without pyridoxal phosphate. Methods The improved reference method without pyridoxal phosphate for AST was established according to the documents of Jonit Committee for Traceability in Laboratory Medicine(JCTLM) and Clinical Chemistry Society of Japan.The precision,accuracy and linear range were evaluated according to the documents of the Clinical and Laboratory Standards Institute(CLSI).The improved reference method was used to evaluate the comparability and calibrate the bias of AST results among 10 different laboratories in Guangzhou.The evaluation was performed before and after a calibration by a common serum calibrator that had a value assigned by the reference method.Results For the measurement with improved reference method,the within-run coefficient of variation(CV) was less than 1%,and the total CV was less than 2%.The biases with target values of JC-ERM and network evaluation results all fulfilled the requirements.The upper limit of the AST measurement range of improved reference method was 413.6U/L.Among the 11 testing systems,the bias of AST fresh serum before calibration compared with the reference method was 20%,and 10 were enzyme activity computed with theoretical K value.The maximum bias of AST results of fresh serum before calibration was-25.0%,and the average bias was 9.3%.Calibrated with enzyme calibrator of the improved reference method,the maximum bias decreased to 12.3%,and the average bias was 2.1%.The average bias of AST results of external quality assessment materials and commercial materials showed no significant difference before and after the calibration.Furthermore,the average bias of the commercial materials increased a little after the calibration.Conclusions The traceability of AST measurement can be effectively improved in different testing systems by using a common fresh serum calibrator that has a value assigned by the reference method.There are some matrix effects in non-fresh-serum calibrators.