Direct ultraviolet method for enzymatic determination of uric acid, with equilibrium and kinetic data-processing options.

We developed and evaluated a direct ultraviolet method for the enzymatic determination of uric acid in serum, plasma, or urine, without deproteinization of sera and plasma. Equilibrium and nonlinear curve-fitting kinetic options are evaluated and compared, and results of the proposed method are compared with those of a candidate Reference Method. All data-processing options yield a linear relation for absorbance and concentration of uric acid between 0.1 and 2 mmol/L; with the equilibrium option, results are linear to 5 mmol/L. For 100 plasma samples, results correlate well between the proposed method (y) and a reference method (x): y = 0.99x - 0.002 mmol/L. Between-run imprecision is about 2.3%, and interference by hemolyzed, icteric, or lipemic specimens or specimens containing high concentrations of xanthine or paraproteins is minimal. The kinetic option with a data-processing range of 100 s or longer yields results that correlate well with the equilibrium method: y = 1.006x + 0.002 mmol/L (n = 118). For 20 urine samples processed by the proposed (y) and a reference (x) methods, y = 1.04x + 0.038 mmol/L.