Simple microdetermination of uric acid.

In 1947 Kalckar introduced a comprehensive differential spectrophotometric system for the analysis of purines, including uric acid (1). Praetorius and his associate Poulsen employed this procedure and have published detailed directions for a practical uric acid method (2, 3). During the past 4 years, over 2000 routine uric acid determinations on blood and urine have been performed in this laboratory by a modification of the Kalckar approach. This modification, while similar to that of Praetorius, provides some features that the present authors feel are more convenient and require less working time. In particular, by use of a more dilute uricase preparation, uric acid destruction proceeds slowly enough to enable the technician to make a single, reliable reading of initial absorbance; he need not record a series of rapidly decreasing absorbances, with final extrapolation back to the initial absorbance. For nearly all samples of urine and serum, determination can be completed within 2 to 4 hours. If desired, however, incubation may be allowed to continue overnight. Experimental evidence is presented that reliable results are obtained, even when an overnight incubation period is employed. A particular advantage of the Kalckar procedure is that it requires no dangerous reagents such as cyanide, which unfortunately is commonly used today in calorimetric methods.