Evaluation of a kinetic uricase method for serum uric acid assay by predicting background absorbance of uricase reaction solution with an integrated method

Abstract

A patented kinetic uricase method was evaluated for serum uric acid assay. Initial absorbance of the reaction mixture before uricase action (A(0)) was obtained by correcting the absorbance at 293 nm measured before the addition of uricase solution, and background absorbance (A(b)) was predicted by an integrated method. Uric acid concentration in reaction solution was calculated from A, the difference between A(0) and A(b), using the absorptivity preset for uric acid. This kinetic uricase method exhibited CV<4.3% and recovery of 100%. Lipids, bilirubin, hemoglobin, ascorbic acid, reduced glutathione and xanthine <0.32 mmol/L in serum had no significant effects. A linearly responded to 1.2 to 37.5 micromol/L uric acid in reaction solution containing 15 microl serum. The slope of linear response was consistent with the absorptivity preset for uric acid while the intercept was consistent with that for serum alone. Uric acid concentrations in clinic sera by different uricase methods positively correlated to each other. By Bland-Altman analysis, this kinetic uricase method accorded with that by quantifying the total change of UV absorbance on the completion of uricase reaction. These results demonstrated that this kinetic uricase method is reliable for serum uric acid assay with enhanced resistance to both xanthine and other common errors, wider range of linear response and much lower cost.

Fig. 1

Bland-Altman analysis of the agreement between different uricase methods for the assay of uric acid in 189 clinic sera. (a) The indirect equilibrium method (C _ie) vs the direct equilibrium method (C _de). Bland-Altman analysis gave C _ie−C _de=−0.002−0.073×((C _ie−C _de)/2) (r>0.698, s=0.039) while the correlation equation between them was C _ie=−0.001+0.927×C _de (r>0.997, s=0.037); (b) This direct kinetic uricase method (C _dk) vs the direct equilibrium method (C _de). Bland-Altman analysis gave C _dk−C _de=−0.019+0.010×((C _de+C _dk)/2) (r<0.137, s=0.037) while the correlation equation between them was C _dk=−0.018+1.007×C _de (r>0.998, s=0.037)

Fig. 1

Bland-Altman analysis of the agreement between different uricase methods for the assay of uric acid in 189 clinic sera. (a) The indirect equilibrium method (C _ie) vs the direct equilibrium method (C _de). Bland-Altman analysis gave C _ie−C _de=−0.002−0.073×((C _ie−C _de)/2) (r>0.698, s=0.039) while the correlation equation between them was C _ie=−0.001+0.927×C _de (r>0.997, s=0.037); (b) This direct kinetic uricase method (C _dk) vs the direct equilibrium method (C _de). Bland-Altman analysis gave C _dk−C _de=−0.019+0.010×((C _de+C _dk)/2) (r<0.137, s=0.037) while the correlation equation between them was C _dk=−0.018+1.007×C _de (r>0.998, s=0.037)