An enzymatic method for the determination of uric acid in whole blood.

In 1939 Blnuch and Koch (1) published an enzymatic method for the calorimetric determination of uric acid in whole blood. This method involves the use of the enzyme uricase for the specific destruction of uric acid. “True uric acid” values were obtained by the difference in the intensity of color produced before and after incubation with the enzyme. The authors reported “true uric acid” values for normal whole blood averaging 2 mg. per cent and non-uric acid chromogenic values, calculated as uric acid, 1 mg. per cent. Recoveries of uric acid added to whole blood before deproteinization averaged 93.5 per cent. Bulger and Johns (2) later published a method similar in principle to that of Blauch and Koch. “True uric acid” was estimated by determining the reduction of alkaline ferricyanide by protein-free filtrates of plasma before and after uricase action. Recoveries of uric acid added to plasma were quantitative. Average values for normal plasma were 4 mg. per cent of “true uric acid” and 1.7 mg. per cent of non-uric acid. These workers suggested, as an explanation of the discrepancy between their results and those obtained by the method of Blauch and Koch (l), that in the latter procedure there is a depression of color development with phosphotungstic acid due to the presence of substances in the tungstate filtrate of blood, which do not, however, influence the reduction of alkaline ferricyanide. A calorimetric modification of the Bulger and Johns method has been recently published by Silverman and Gubernick (3). Lower non-uric acid values than Bulger and Johns reported were obtained by these workers (less than 1.0 mg. per cent) ; however, this procedure is still not applicable to whole blood. In view of the fact that there are many inherent errors in the Blauch and Koch (1) method and that the Bulger and Johns (2, 3) procedure is somewhat involved and cannot be applied to whole blood, we thought it worth while to reinvestigate the problem and to attempt to develop a specific