Colorimetric measurement of uric acid.

HEN ASKED IN 1942 to find a method for the determination of plasma or serum uric acid suitable for inclusion in the War Department’s Technical Manual 8-227, Method,s for Laboratory Technicians, the author believed that the procedure of Kern and Stransky (1) filled the requirements admirably. In this modification, toxic and heat-labile sodium cyanide solution wa replaced by the effective but nontoxic and relatively stable glycerine-silicate reagent. However, when the method of Kern and Stransky was used exactly as directed, colored solutions quickly became turbid when the glycerine-silicate used was prepared from either a diluted water-glass preparation or from a solid silicate. Furthermore, use of any one of the available preparations of glycerine resulted in a reagent mixture which permitted development of turbidity. As Kern and Stransky made no mention of such turbidity, it seems likely that the glycerine preparations available to them contained some impurity which inhibited precipitation from the glycerine-silicate mixture. In any case, addition of Liquoid La Roche, a Swiss preparation of sodium polyanethol sulfonate, consistently prevented development of turbidity in the colored solutions. No adequate substitute for this sulfonate was found. The first few batches of Liquoid prepared in this country were also unable to prevent development of turbidity. However, batches of Liquoid marketed by Hoffman-La Roche, Inc., during the past ten years appear to be completely satisfactory. To decrease the number of reagents required for conduct of this procedure, the protein precipitant (uranyl acetate) employed by Kern and Stransky was replaced by the reagent used for the development of color. Thus, the phosphotungstic acid reagent serves not only for the development of color, but also for the precipitation of blood proteins.