Background/Purpose: Gout is an inflammatory disease resulted from an increased body pool of uric acid. The measurement of 24-hour uric acid excretion is important to evaluate the disease status as well as to select the kind of uric acid lowering agents. However, 24-hour urine collection is inconvenient, and frequently unreliable due to errors in collection. The average person excretes approximately 1 g/day creatinine, and thus a lot of studies showed that the random urine protein to creatinine ratio was well correlated with 24-hour urine protein excretion rate. In this study, we investigated the utility of the random urine uric acid to creatinine ratio for predicting 24-hour urine uric acid excretion in gouty patients.

Methods: The cross-sectional study included 37 gouty patients without any use of uric acid lowering agents. The average age was 47.7 ± 17.7 years old and 34 out of 37 were male patients. 24-hour urine collections of the patients were conducted to the evaluate uric acid excretion and renal function. Random urine uric acid and creatinine specimens were obtained from all participants at the day when 24-hour urine collection was conducted. The creatinine clearance (CCr) was measured from the 24-hour urine collected sample, and chronic kidney disease was defined as the CCr levels below 60 ml/min/1.73m².

Results: The mean of 24-hour uric acid excretion was 602.4 ± 236.0 mg, and those of serum uric acid levels and CCr values were 7.31 ± 1.31 mg/dl and 100.9 ± 33.2 ml/min/1.73m², respectively. Random urine uric acid to creatinine ratio was closely correlated with the absolute and log transformed 24-hour urine uric acid excretions (γ = 0.450, p = 0.005;γ = 0.474, p = 0.003, respectively). In the linear regression analysis, the amount of absolute 24-hour urine uric acid excretion was estimated by 0.812 x (random urine uric acid to creatinine ratio) + 290.466 (R² = 0.450, p = 0.005). The correlation between random urine uric acid to creatinine ratio and 24-hour urine uric acid excretion was also found in the patients with chronic kidney disease (γ = 0.900, p= 0.037). 

Conclusion: Random urine uric acid to creatinine ratio showed positive correlation with the absolute and log transformed 24-hour urine uric acid excretions. The random urine uric acid to creatinine ratio would be a good predictor of 24-hour urine uric acid excretion in gouty patients.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-random-urine-uric-acid-to-creatinine-ratio-as-a-predictor-of-24-hour-urine-uric-acid-excretion-in-gout-patients/