Determination of serum urate by direct acid Fe3+ reduction or by absorbance change (at 293 nm) on oxidation of urate with alkaline ferricyanide.

An acid ferric reduction procedure is described for determining serum urate with 2,4,6-tripyridyl-s-triazine at 593 nm, whereby each mole of urate reduces 4 moles of ferric ion. The procedure requires no deproteinization and as little as 20 l of serum is needed. It gives results that are linearly related to concentration to about 30 mg/dl, and it is precise (CV, 2.6%), accurate, and sensitive (a = 538). An ultraviolet spectrophotometric procedure is also described, in which urate is determined from the difference in absorbance at 293 nm with and without alkaline ferricyanide oxidation of urate. This procedure also is linear to at least 15 mg/dl, precise (CV, 1.2%), and accurate. Results by both procedures agree and correlate well with a reference uricase method. More than 99% of urate added to serum can be accounted for analytically.