Xanthine interference in the Kodak "Ektachem" determination of uric acid.

In connection with studiesrelated to the purines in serum of leukemia patients (1), xanthine interference was observed in the Kodak Ektachem enzymically based determination of uric acid, leading to significant underestimation of the latter’s actual concentration-a finding that agrees with a previous report (2). In hereditary xanthinuria, total oxypurine concentrations in serum ranged from 1 to 9 mg/L (3). In normal children, values for hypoxanthine and xanthine were 1.2 ± 1.2 and 3.7 ± 3.4 mg/L (mean ± SD), respectively. However, in leukemia patients undergoing acute tumor lysis and in renal failure, hypoxanthine and xanthine concentrations were respectively 28 ± 14.9 and 158 ± 72.6 mg/L (4). Because such purine concentrations can occur clinically, the inhibitory phenomenon needed closer investigation. Hypoxanthine and monosodium xanthine were added to pooled normal serum, and the final concentrations were verified by paper chromatography. Uric acid was determined according to the manufacturer’s instructions. Interference with uric acid determination was first observed at a xanthine concentration of 100 mg/L in serum, and an essentially linear relationship between the xanthine concentrations from 156 to 520 mg/L and the range of interference from 10% to 36.5% was established: