ABSTRACT
Objective To investigate the efficacy of using a calibrator with values assigned with the reference method for improving the comparability of serum gamma-glutamyltransferase (GGT) measurements.Methods The IFCC reference method for GGT was established and the performance was verified by testing a certified reference material (CRM).A calibrator was prepared and its value for GGT was assigned with the reference method.Forty serum samples were measured on different (including HITACHI 7600,7060,7170,7180 and BECKMAN LX20,OLYMPUS AU 400) chemistry analyzers with Zhongsheng GGT reagent kits calibrated with the calibrator.The samples were also measured on the same analyzers using a theoretical factor.Biases of results obtained with the calibration and with the theoretical factor based calculation were compared.Results The reference method resuhs on the CRM agreed the certified value within the stated uncertainty.Serum results calculated from the theoretical factor showed various biases and inter-analyzer variations.When the analyzers were calibrated with the calibrator,the number of results with biases less than 10% became significantly higher and those with biases more than 20% significantly lower.The variation of the results on 5 serum samples was reduced from 11.0%～14.0% to less than 5% by using the calibrator.Conclusion Accuracy and comparability of GGT measurements with of ZhongSheng GGT kits can be improved by using a calibrator that has a value assigned with the reference method.
ABSTRACT
Objective To investigate the accuracy and comparability of ?-glutamyltransferase (?- GT) measurement results on human serum samples and controI materials before and after calibration with a common human serum calibrator.Methods A human serum calibrator was prepared by pooling fresh serum aliquots and assigning a value for ?-GT with the IFCC reference method.The calibrator together with 5 human serum samples and 10 control samples were sent to 15 clinical laboratories and the sermn and control samples were measured with different analytical systems before and after a calibration with the calibrator.The results were analyzed for biases and interlaboratory variations.Results For the serum samples,the calibration resulted in reductions in biases from -9.0%～-14.2% to -0.8%～-7.9%,and in interlaboratory variations from 6.9%～11.6% to 2.8%～4.4%.No improvement was observed on the control samples.Conclusions Accuracy and comparability of serum ?-GT measurements can be improved by using a common human serum calibrator.Some control materials may not be commutable for human serum in ?-GT measurements.