Kinetic and equilibrium assays for glucose on the Cobas Bio centrifugal analyzer, with use of the glucose dehydrogenase reaction.

15 16 17 18 19 initiation and again after 360 s when the reaction is complete. The difference between the two readings closely apGDH, proximates the equilibriumabsorbance equlGDH, change. The rate determination uses an llbrium rate initial rate calculation. A set of seven g/L g/L absorbance readings is fit by linear re0 0 gression. The slope of the regression line 2.00 2.00 approximates the initial velocity of the 2 00 2 00 reaction and is directly proportional to glu ose co centrat on. 2.00 2.00 The standard curve with aqueous 7.00 7.00 standards was linear to 7.00 g/L for both 37.0 37.0 assays. Deviation from linearity was less than 4.0% at 10.0 g/L for both methods. 340 340 Sensitivity, expressed as the glucose concentration giving 0.001 i.A, averaged 03 04 0.0026 and 0.020 g/L for the endpoint 50 40 and rate methods, respectively. Dilu250 200 tions of human serum supplemented 0 0 with pure glucose were linear to 7.00 g/L 0 0 for both assays. Within-run precision was assessed by 10.0 running replicates of normal and ab10 normal human sera, and day-to-day 02 07 precision by running lyophilized control 1 1 sera (Table 2). The two methods gave 1 2 similar precision. Although the rate method has lower sensitivity than the endpoint method, precision is well maintained, because the use of multiple data points in the rate assay offsets variation associated with lower sensitivity. A set of60 human serawere analyzed by the GDH methods and the manufacturer’s hexokinase method. Regression parameters for comparison of hexokinase (x) and GDH equilibrium (y) were: slope = 0.994, intercept = 0.038, standard error of estimate = 0.018,and correlation coefficient = 0.999. Regression parameters for comparison of hexokinase (x) and GDH rate (y) were: slope = 0.958, intercept = 0.073, standard error of estimate = 0.027, and correlation coefficient = 0.999. Both GDH methods gave results in excellent agreement with the hexokinase comparison method. Our data demonstrate excellent performance for both GDH procedures.