Trueness verification and traceability assessment of results from a routine chemistry system for measurement of urea and creatinine in serum

Objective To verify the trueness and assess the traceability of results from a routine chemistry system procedure for measurement of urea and creatinine in serum. Methods Series of fresh frozen patient sera, whose values of urea or creatinine were assigned by isotope dilution gas chromatography mass spectrometry (ID-GC/MS) or isotope dilution liquid chromatography tandem mass spectrometry (ID-LC/MS/MS), were chosen to be analyzed by a routine chemistry system.The measurement results of urea and creatinine by the routine chemistry system were used for linear regression analysis against the assigned values by the ID-MS method to calculate the percentage deviation and assess the expected bias. Results For urea and creatinine, the linear regression equations between the routine chemistry system and ID-MS methods were Y=0.9890X+0.0192 (R2=0.9990) and Y=0.9815X-6.4794 (R2=0.9989), and the average percentage bias were -0.41% (P>0.05) and -4.20% (P<0.05), respectively.The expected percentage bias at three medical decision levels were -0.46%, -0.83% and -0.96% for urea and -15.90%, -5.87% and -2.95% for creatinine. Conclusions The results of urea analyzed by the routine chemistry system were consistent with the ID-MS method, which suggested that the results of the routine system procedure could be traced to ID-GC/MS method.For creatinine, the bias between the results of routine procedures and the assigned values met the 'minimum acceptance criteria' derived from biologic deviations, which would be better if its specificity improved.（Chin J Lab Med，2012,35：912-915） Key words: Urea; Creatinine; Gas chromatography-mass spectrometry; Bias (epidemiology)