Kidney stone composition in overweight and obese patients: a preliminary report

OBJECTIVE To report preliminary information on urinary stone composition in patients who are either overweight or obese with kidney stone disease. METHODS A cohort of patients (n = 138) with nephrolithiasis were prospectively followed from January 2011 for 18 months. Of those, 64 (46%) were found to be overweight with body mass index ≥ 25 kg/m(2) and 74 (54%) were obese with body mass index ≥ 30 kg/m(2). Stone characteristics including size, location, and composition were studied in detail, and patients' age, weight, height, and gender were all documented. The stone size and location were studied radiologically while semiquantitative stone analysis was carried out using the DiaSys method, which involves titrimetric determination of calcium, colorimetric determination/visual assessment of oxalate, phosphate, magnesium, ammonium, uric acid, and cystine, and qualitative determination of carbonate. RESULTS Eighteen stones were collected from overweight and obese patients. Those obtained were either spontaneously passed (n = 2), fragments passed following shockwave lithotripsy (n = 11), extracted ureteroscopically (n = 2), or extracted by percutaneous nephrolithotomy (n = 3). About 95% of the stones contained calcium oxalate and more than half contained uric acid. CONCLUSION This report confirms that kidney stones are mainly composed of calcium oxalate and uric acid in overweight and obese patients with nephrolithiasis.