The impact of obesity on urine composition and nephrolithiasis management

Several studies have reported that obese patients have a higher risk of nephrolithiasis. The purpose of this study is to investigate the effect of overweight (OW) and obesity on stone composition, type of treatment, and urine composition.

With Institutional Review Board approval, charts of adult patients who attended our dedicated stone clinic over a 5-year period starting January 2006 were reviewed. Patients were categorized into normal (body mass index 18.5-24.9), OW (25-29.9), and obese (≥30). We excluded those who did not have at least one 24-hour urine analysis.

OW and obese patients were more likely to have previous stones, more chance to have uric acid stones, and to be treated with shockwave lithotripsy in the community, and with ureteroscopy or percutaneous nephrolithotripsy in our center. They needed more thiazide diuretics, allopurinol, and dietitian counseling. They had statistically significant (P<0.05) higher urine calcium, citrate, supersaturation calcium phosphate, uric acid, supersaturation uric acid, sodium, potassium, magnesium, phosphorus, chloride, sulfate, urine urea nitrogen, protein catabolic rate, and creatinine compared with those with normal weight.

OW and obese patients have different stone composition with increased excretion of stone promoters in the urine. Stone prevention measures should be introduced during metabolic syndrome evaluation.