Impact of obesity in patients with urolithiasis and its prognostic usefulness in stone recurrence

Purpose: Recent studies have suggested an increased prevalence of urolithiasis and recurrence associated with obesity. We assessed the influence of obesity on stone risk factors as well as on stone recurrence. Materials and Methods: A database of patient history, body mass index, and serum and urine chemistry was analyzed for 704 consecutive stone formers (467 first time stone formers and 247 recurrent stone formers). Obesity was defined as body mass index greater than 25 kg/m(2). The effect of obesity on stone risk factors and recurrence were stratified according to stone episodes. Of these, 163 (23.2%) patients who had been followed for more than 36 months (median 54, range 5 to 148) were included in recurrence analysis. Results: Obesity was significantly associated with stone episodes (p = 0.043). Obese stone formers excreted increased amounts of sodium, calcium, uric acid and citrate, while the urinary pH in a 24-hour urine sample was decreased compared to nonobese stone formers (p < 0.05, respectively). Stone analysis revealed that uric acid stone was significantly more commonly found in the obese patients (p = 0.046). Multivariate Cox regression model stratified by stone episodes revealed that obesity (HR 2.572, 95% CI 1.376-4.807, p = 0.003) was the only strong predictor of stone recurrence in first time stone formers. No association between obesity and stone recurrence was detected in recurrent stone formers. Kaplan-Meier curves showed identical results. Conclusions: This study reveals that obesity is associated with metabolic alterations and urinary stone recurrence. Weight control may be considered one of the preventive modalities against recurrent stone formation, especially in first time stone formers.