Impact of body weight on urinary electrolytes in urinary stone formers

Objectives. Obesity increases the risk of developing chronic medical condit ions such as diabetes mellitus, hypertension, and coronary artery disease. We performed a retrospective review of a large data base on urinary stones to determine if differences are found in urine and serum chemistries among obese and nonobese stone-forming patients. The effect of body weight on sto ne recurrence among urinary stone formers was also determined. Methods. A national data base containing serum biochemical profiles, 24-hou r urine specimens, and standardized questionnaires was retrospectively eval uated from 5942 consecutive patients with urinary stone disease. Stone-form ing patients were classified by body weight: nonobese men, less than 100 kg and nonobese women, less than 85 kg; intermediate men, 100 to 120 kg and i ntermediate women, 85 to 100 kg; and obese men, more than 120 kg and obese women, more than 100 kg. Results. Obese stone formers comprised 6.8% (n = 404) of the patient popula tion. The mean weight in the nonobese and obese groups was 81 kg versus 134 kg, respectively, for men and 64 kg versus 112 kg, respectively, for women . Obese patients represented 3.8% of the male and 12.6% of the female popul ation. Obese patients had increased urinary excretion of sodium, calcium, m agnesium, citrate, sulfate, phosphate, oxalate, uric acid, and cystine; obe sity was associated with increased urinary volumes and urine osmolality com pared with the nonobese patients. Obese men had increased concentration of urinary sodium, oxalate, uric acid, sulfate, and phosphate when corrected f or urinary volume. Obese women had increased concentrations of sodium, uric acid, sulfate, phosphate, and cystine. The mean number of stone episodes i n nonobese versus obese men was similar (3.55 and 3.56), whereas mean stone episodes were 2.93 and 3.38 (P = 0.045) for nonobese versus obese women. Conclusions. Among known stone formers, obesity is associated with unique c hanges in both serum and urinary chemistries. These changes are associated with an increased incidence of urinary stone episodes in obese women but no t in obese men. UROLOGY 55: 825-830, 2000. (C) 2000, Elsevier Science Inc.