Two Ultramicro-Scale Methods for Plasma Uric Acid Analysis with Uricase

Abstract

Results with two ultramicro methods for plasma uric acid analysis with uricase are described: a crystal violet (gentian violet) method, modified from an automated procedure by Gochman and Schmitz [Clin. Chem. 17, 1154 (1971)] and adapted to manual analysis, and a polarographic oxygen-sensing system (Beckman Instruments, Inc.). The coefficient of variation (CV) for the crystal violet method varied between 2.1 and 5.7% for an 11-month period. Within-run precision (CV) of the polarographic method was 3.3%; day-to-day CV varied between 3.4 and 9.4%. Percentage recovery for the crystal violet method ranged between 97 and 106%, and for the polarographic method between 92 and 100%. Results of the two methods correlate well, but 5-15% lower values are obtained by the crystal violet method than by the polarographic method. Bilirubin, hemolysis, or usual plasma concentrations of ascorbic acid do not interfere significantly with either method. Advantages and disadvantages of both methods are discussed. The polarographic method requires more uricase, but is the better of the two methods.