Difference in urinary stone components between obese and non-obese patients.

The prevalence and incidence of urinary stone disease have been reported to be associated with body weight and body mass index (BMI). The aim of the study was to determine the difference in stone components among different BMI groups in patients with urolithiasis. Between Dec 2005 and Jan 2008, 907 urinary calculi were collected and analyzed by infrared spectroscopy. Most of the stones had been passed spontaneously, and some were collected during surgical manipulations. The data on patients' gender, age, BMI at diagnosis, and stone composition were collected. The patients were classified as normal weight (18.5≤ BMI <24), overweight (24≤ BMI <27), or obese (BMI ≥27). Of the 907 patients with urinary stone disease, 27.7% had normal weight, 33.5% were overweight, and 38.8% were obese. The prevalence of calcium oxalate stones in the normal weight, overweight, and obese groups were 23.1, 30.6, and 34.9%, respectively (P = 0.002), and the prevalence of uric acid stones in the different groups was 2.8, 7.2, and 7.7%, respectively (P = 0.002). The prevalence of calcium oxalate and uric acid stones, but not that of calcium phosphate stones, increased with body size. There was a significant correlation between BMI and uric acid stones in the overweight and obesity groups, with odds ratios of 3.28 and 4.35, respectively. The prevalence and incidence of urinary stone disease were found to be associated with BMI. The percentage of uric acid and calcium oxalate stones was higher in obese than in non-obese patients. There was no apparent difference in the prevalence of calcium phosphate stones between obese and non-obese patients.