Local factors compared with systemic factors in the formation of bladder uric acid stones

The aim of this study was to evaluate the clinical characteristics of uric acid urolithiasis and how the presentation differs between urolithiasis of the upper urinary tract (UUT) compared with urolithiasis of the bladder. We attempted to evaluate the importance of local vs. systemic factors in the formation of bladder uric acid stones.

The medical records of 77 consecutive patients with uric acid urolithiasis from January 2004 to December 2006 were reviewed retrospectively. In all patients, histories were recorded, and physical examinations, renal function tests and urine analysis were done. The features of the treated stones were recorded, and the chemical composition was analyzed by computed Fourier transform infrared spectrophotometry.

Among 77 patients with uric acid stones, 66 were male and 11 were female (ratio of 7.6:1). Mean age was 59.50 +/- 10.46 years. Of the stones, 55 (71.4%) were located in the UUT (UUT group) and 22 (28.6%) in the bladder (bladder group). Multiple presentations of urolithiasis at diagnosis were found in 56 (72.7%) patients. The mean values of serum creatinine and uric acid were 148.28 +/- 70.69 and 443.33 +/- 95.91 micromol/l, respectively. Mean body mass index (BMI) was 26.78 +/- 2.90, and 72.7% of patients were overweight or obese. Mean urinary pH was 5.39. No significant differences existed between the 2 groups in regard to gender, BMI, urinary pH, stone nature, or presence of hypertension, gout, and/or urinary tract infections. In the bladder group, the incidence of benign prostate hyperplasia was significantly increased, and the incidence of diabetes mellitus was significantly lower, as were levels of serum uric acid and creatinine.

Uric acid urolithiasis was predominant in men in this study. These patients tended to be obese or overweight, with multiple stone presentations and low urinary pH. Furthermore, the bladder uric acid stone group had significantly lower levels of serum creatinine and uric acid, and lower percentages of diabetes mellitus but higher incidences of benign prostate hyperplasia in comparison with the UUT group. The local factor seems more important than the systemic factor in the formation of bladder uric acid stone.