PURPOSE: To carry out the accurate calorimetry without being affected by bilirubin, etc. by measuring hydrogen peroxide produced by uric acid.uricase reaction, etc. under the existence of metallic azide compound.

CONSTITUTION: An uricase solution containing uricase, 4-amino antipyrin in 0.05M phosphoric acid buffer solution (8.0pH) is used for the uricase solution and a peroxidase solution containing peroxidase, 3-methyl-N-ethyl-N-hydroxyethyl aniline in 0.15M phosphoric acid buffer solution (5.0pH) is used for the peroxidase solution and then, 550nm wavelength is used for measuring the wavelength. 100μl blood serum or a standard solution of uric acid, is sampled and 1.0ml uricase solution is added and then, is mixed. Further, reaction is carried out for a constant time in a 27°C thermostat and next, 20ml peroxidase solution is added and is mixed. Absorbance is measured after reacting two minutes in said thermostat and it is shown by the figure. The accurate calorimetry is carried out from this result because the uricase solution added sodium azide does not decompose hydrogen peroxide.