The determination of uric acid in biological materials.

Uric acid is commonly determined in biological fluids by measuring the blue colour produced by its reaction with reagents containing phosphotungstic or arsenotungstic acids under conditions which minimize interference by other reducing substances (Folin & Denis, 1912; Folin, 1933, 1934; Benedict, 1912, 1922; Brown, 1945; Bidmead, 1951). Recovery of uric acid added to blood has never been complete and values as low as 50% have been recorded. Substances other than uric acid which react with the reagents occur in blood, notably ergothioneine (Hunter & Eagles, 1925) which occurs mainly in the erythrocytes. Benedict & Behre (1931) found that ergothioneine is removed when silver chloride is precipitated in the solution. Treatment with the enzyme uricase has been used to distinguish uric acid from other reacting substances (Blauch & Koch, 1939; Bulger & Johns, 1941; Block & Geib, 1947; Johnstone, 1952). The present paper describes experiments which have led to a satisfactory method for the assay of uric acid with a phosphotungstic acid reagent.