Method Comparison and Bias Estimation of Blood Urea Nitrogen (BUN), Creatinine (Cr), and Uric Acid (UA) Measurements between Two Analytical Methods.

BACKGROUND: A comparison of any two methods is of great importance in a clinical laboratory. In this study, our aim is to compare the assay results of blood urea nitrogen (BUN), creatinine (Cr), and uric acid (UA) obtained through two distinct methods and then assess the analytical agreement of the two methods.

METHODS: A test method (Vitros5600 system) measuring BUN, Cr, and UA analytes was compared with a reference method (Hitachi7600 system). The Clinical and Laboratory Standards Institute (CLSI) document EP9-A2 guidelines were followed to evaluate the method comparison and bias using 40 patient samples.

RESULTS: A high correlation between the two methods was found for all of the samples (R2 > 0.990). The regression parameters were BUN (R2 = 0.9996, slope = 1.025, intercept = 0.1156), Cr (R2 = 0.9993, slope = 0.9993, intercept = 4.661), and UA (R2 = 0.9971, slope = 1.011, intercept = 1.311). Compared with the Hitachi7600 reference method, the Vitros5600 test method showed that the 95% confidence interval for the predicted bias at medical decision levels was less than the acceptable error. More importantly, Bland-Altman plots indicated that a minimal positive bias (mean ± SD) was observed: BUN (0.352 ± 0.289 mmol/L), Cr (2.702 ± 7.683 µmol/L), UA (5.398 ± 7.086 µmol/L).

CONCLUSIONS: The Vitros5600 and Hitachi7600 systems have good correlation and bias for detecting BUN, Cr, and UA analytes. The two systems have a high method agreement.