Limited value of uric acid to creatinine ratios in estimating uric acid excretion.

The value of the uric acid to creatinine ratio and the uric acid to creatinine clearance ratio in predicting 24-hour urinary uric acid excretion was assessed in 49 patients with normal enzyme activity and 22 patients with purine enzyme deficiencies. A 24-hour urinary uric acid to creatinine ratio greater than 0.75 was found in six of nine patients with a partial deficiency of hypoxanthine-guanine phosphoribosyltransferase and in all patients with Lesch-Nyhan syndrome. A ratio of less than 0.10 suggested xanthinuria or severe purine nucleoside phosphorylase deficiency. Neither ratio calculated from 2-hour timed collections of the 24-hour specimen showed a high correlation with 24-hour urine uric acid excretion in patients with normal enzyme activity, perhaps because of a diurnal variation in urinary uric acid excretion. The spot-urine uric acid to creatinine ratio does not accurately predict the 24-hour urine uric acid excretion in patients with normal enzyme activity.