THE UTILITY OF SPOT URINE URIC ACID TO CREATININE RATIO FOR PREDICTOR OF 24-HOUR URINE URIC ACID EXCRETION IN GOUTY PATIENTS

Abstract

Background Gout is an inflammatory disease resulted from hyperuricemia. The measurement of 24-hour urine uric acid excretion is important not only to evaluate the disease status but also to choose the kind of uric acid lowering agents. 24-hour urine collection, however, is cumbersome, inconvenient, and often unreliable because of errors in collection. The average person excretes approximately 1 g of creatinine per day, and a lot of studies showed that the spot urine protein to creatinine ratio was correlated with 24-hour urine protein excretion.

Objectives In this study, we investigated the utility of the spot urine uric acid to creatinine ratio for predicting 24-hour urine uric acid excretion in gouty patients.

Methods Fifty-one gouty patients without any use of uric acid lowering agents were enrolled in this study. The average age was 48.1±17.1 years old and 90.2% (46/51) were male patients. 24-hour urine collections of the patients were conducted to the evaluate uric acid excretion and renal function. Spot urine uric acid and creatinine specimens were obtained from all participants at the same day when 24-hour urine was collected. The creatinine clearance (CCr) was measured from the 24-hour urine collected sample, and chronic kidney disease was defined when their CCr level was below 60 ml/min/1.73m2.

Results The mean of 24-hour uric acid excretion was 643.5±259.2 mg, and those of serum uric acid levels and CCr values were 7.45±1.35 mg/dl and 103.5±41.8 ml/min/1.73m2, respectively. Spot urine uric acid to creatinine ratio was significantly correlated with the absolute and log transformed 24-hour urinary uric acid values (γ =0.410, p =0.003; γ =0.610, p <0.001, respectively). In the linear regression analysis, the amount of absolute 24-hour urine uric acid excretion was estimated by 0.799 x (spot urine uric acid to creatinine ratio) + 336.239 (R2 =0.410, p =0.003). The correlation between spot urine uric acid to creatinine ratio and 24-hour urine uric acid excretion was also found in the patients with chronic kidney disease (γ =0.964, p <0.001).

Conclusions Spot urine uric acid to creatinine ratio showed well correlation with the absolute and log transformed 24-hour urine uric acid excretions. The spot urine uric acid to creatinine ratio could be a good predictor of 24-hour urine uric acid excretion in gouty patients.