A new automated uric acid assay.

Currently, the most popular automated method for the determination of serum uric acid is the automated method modified by Musser and Ortigoza (1966) for the TechniconS AutoAnalyzer system. While this method is considered reliable, it suffers from the following deficiencies: (a) it shows non-linearity with dilutions of aqueous uric acid standards and is thus dependent on costly reference sera as secondary standards; (b) it has been found to give results which are 14% higher than the manual uricase reference method of Liddle et al. (1959) according to Technicon's literature2, and approximately 0-6 mg/dl (0-036 mmol/l) higher according to Itiaba et al. (1975); (c) recovery is incomplete and aqueous standards containing formaldehyde, which is traditionally used as a preservative, give grossly incomplete recovery (Klein and Sheehan, 1937); and (d) a high concentration of costly sodium tungstate is used as one of the reagents in this method. In a preliminary study with the SMA 12/60 (unpublished data), we observed non-linearity of aqueous uric acid standards introducing errors up to 30%. On calibrating the SMA 12/60 with the aqueous uric acid standards, similar non-linearity persisted affecting the sera values. In order to overcome some of these difficulties generally encountered with the continuous-flow automated methods, we selected the unique reagent system of Jung and Parekh (1970) for purposes of automation. As a result of our investigation we have been able to present in this paper an automated uric acid assay, which is free of most of the aforementioned problems. More significantly, the applicability of primary uric acid standards (with or without formaldehyde) in the proposed assay has enhanced the analytical accuracy of uric acid measurements in clinically important biological fluids