Background/Purpose: Gout is a chronic inflammatory disease resulted from hyperuricemia. The measurement of 24-hour urinary uric acid excretion is frequently used to evaluate disease status and select drugs that lower uric acid level. However, 24-hour urine collection is cumbersome and inconvenient, and sometimes unreliable because of incomplete sampling. Approximately 1 g of creatinine is excreted into the urine on a daily basis, and the ratio of random urine protein to creatinine is known to be closely related to the amount of 24-hour urine protein excretion. Therefore, in this study, we assessed the utility of the random urinary uric acid/creatinine (UA/Cr) ratio in the estimation of 24-hour urine uric acid excretion in patients with gout.

Methods: Eighty-seven patients with gout without any use of uric acid lowering agents were enrolled in this study. The mean age was 49.8 ± 16.8 years old and the male patient was 89.6% (78/87). For the evaluation of uric acid excretion and renal function, patients were collected 24-hour urine. Random urine uric acid and creatinine specimens were gained on the same day of 24-hour urine collection. Chronic kidney disease was defined as a creatinine clearance (CCr) level of less than 60 ml/min/1.73m² measured in 24-hour urine collection sample. Excretion of more than 650 mg of uric acid in the 24-hour urine sample was defined as uric acid over-excretion.

Results: Mean serum uric acid level was 7.77 ± 1.92 mg/dl, and the mean 24-hour uric acid excretion and mean CCr value were 669.6 ± 237.9 mg and 109.6 ± 39.0 ml/min/1.73m^2,, respectively. Random urinary UA/Cr ratio showed good correlation with the 24-hour urine uric acid excretion in the absolute and log-transformed value (γ = 0.413, p < 0.001; γ = 0.585, p <0.001, respectively). Correlation between these two variables was also found in the patients with chronic kidney disease (γ = 0.789, p = 0.011). In the linear regression analysis, absolute 24-hour urine uric acid excretion was estimated to be 402 x (random urinary UA/Cr ratio) + 218.73 (p < 0.001). The best cut-off value for the random urinary UA/Cr ratio to distinguish between uric acid over-excretion and normal uric acid excretion was 0.533, and its sensitivity and specificity were 35.6% and 97.6%, respectively (AUC = 0.686; 95% CI, 0.576 – 0.796, p = 0.003).

Conclusion: There was a good correlation between the random urinary UA/Cr ratio and 24-hour urine uric acid excretions. The random urinary UA/Cr ratio would be a useful predictor of 24-hour urine uric acid excretion in patients with gout.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/random-urinary-uric-acidcreatinine-ratio-is-useful-in-the-estimation-of-24-hour-urine-uric-acid-excretion-in-patients-with-gout/