IMPROVED FLUOROMETRIC QUANTIFICATION OF URINARY XANTHURENIC ACID

Measurement of urinary xanthurenic acid (XA) has been used clinically to study a variety of disorders caused by vitamin B-6 deficiency. To o bviate some cumbersome steps of current methods for measuring XA in hu man urine, we have developed a simple fluorometric method, We apply th e urine sample to a solid-phase extraction column containing trimethyl aminopropyl group bound to silica, which enables us to purify and conc entrate the XA from the urine without contamination from various trypt ophan metabolites. The XA in the acidic eluate can then be quantified fluorometrically, The linearity of the proposed method extends from 0. 2 to 10.0 mg/L. The method is precise, yielding day-to-day CVs for two pooled control specimens (1.08 and 1.90 mg/L) of 1.2% and 2.6%, respe ctively. Correlation studies with an established HPLC method and with a spectrophotometric procedure showed correlation coefficients of 0.99 and 0.98, respectively, Interference from vitamin C, uric acid, salic ylate, acetaminophen, vanillylmandelic acid, and homovanillic acid was insignificant. The proposed method for urinary XA is rapid, simple, a nd suitable for routine use in the clinical laboratory.