In recent decades there has been an increasing prevalence of urolitithiasis in many western countries and at the same time there has been an increasing progression of obesity that has reached epidemic proportions. The aim of the present study was to assess the influence of overweight/obesity on the metabolic risk factors for renal stone formation. We studied 799 renal stone formers (462 men and 337 women) who came to the clinic for metabolic risk factors evaluation. They were all studied with a standard protocol (two 24-h urine collections and serum parameters). They were divided according to their BMI in normal (BMI < 25) overweight (BMI 25-29.9) and obese (BMI > 30). Low-weight individuals were excluded. Overall, 487 of 799 (60.9%) patients had a BMI > 25, including 40.6% overweight and 20.3% obese. Among women 55.2% had normal weight, 25.5 were overweight, and 19.3% were Obese; among men 27.3% had normal weight, 51.7 were overweight, and 21% were obese. Age increased significantly with increasing BMI both in men and women. In women there was a significant increase in the excretion of oxalate, uric acid, phosphorus, creatinine, and sodium with increasing BMI, but no change was observed in calcium, magnesium, citrate, and urine pH. In men there was a significant increase in the excretion of oxalate, uric acid, creatinine, phosphorus, sodium, magnesium, and citrate with increasing BMI, no change in urinary calcium and significant progressive decrease in urinary pH. In this population of stone formers there was a high prevalence of overweight/obesity (60.9%). Both in men and women we found a significant increase in the urinary excretion of two promoters of stone formation, oxalate, and uric acid but no change in urinary calcium. There was either no change or increase in magnesium and citrate, inhibitors of crystallization, and a significant decrease in urine pH only in men.

The purpose of the present study was to compare the clinical characteristics of "pure" uric acid (UA) stone formers with that of "pure" calcium oxalate (CaOx) stone formers and to determine whether renal handling of UA, urinary pH, and urinary excretion of promoters and inhibitors of stone formation were different between the two groups. Study subjects comprised 59 patients identified by records of stone analysis: 30 of them had "pure" UA stones and 29 had "pure" CaOx nephrolithiasis. Both groups underwent full outpatient evaluation of stone risk analysis that included renal handling of UA and urinary pH. Compared to CaOx stone formers, UA stone formers were older (53.3 +/- 11.8 years vs. 44.5 +/- 10.0 years; P = 0.003); they had higher mean weight (88.6 +/- 12.5 kg vs. 78.0 +/- 11.0 kg; P = 0.001) and body mass index (29.5 +/- 4.2 kg/m(2) vs. 26.3 +/- 3.5 kg/m(2); P = 0.002) with a greater proportion of obese subjects (43.3% vs. 16.1%; P = 0.01). Patients with "pure" UA lithiasis had significantly lower UA clearance, UA fractional excretion, and UA/creatinine ratio, with significantly higher serum UA. The mean urinary pH was significantly lower in UA stone formers compared to CaOx stone formers (5.17 +/- 0.20 vs. 5.93 +/- 0.42; P < 0.0001). Patients with CaOx stones were a decade younger, having higher 24-h urinary calcium excretion (218.5 +/- 56.3 mg/24 h vs. 181.3 +/- 57.1 mg/24 h; P = 0.01) and a higher activity product index for CaOx [AP (CaOx) index]. Overweight/obesity and older age associated with low urine pH were the principal characteristic of "pure" UA stone formers. Impairment in urate excretion associated with increased serum UA was also another characteristic of UA stone formers that resembles patients with primary gout. Patients with pure CaOx stones were younger; they had a low proportion of obese subjects, a higher urinary calcium excretion, and a higher AP index for CaOx.

Urolithiasis is the third most common pathological disease afflicting the urinary tract, and usually occurs between the third and fourth decades of an individual's life. Epidemiological studies about this condition are lacking in our country. In 1998, we performed an epidemiological, cross-sectional study of the prevalence of urolithiasis in a sample of 1,086 subjects, which included men and women of all ages, selected from the general population of the city of Buenos Aires. The method used to gather basic information was an auto administered questionnaire about the present or past history of urolithiasis that was handled at the dwelling by a trained volunteer. We found a 3.96% lifetime prevalence of urolithiasis in the general population of Buenos Aires. The rate was slightly higher in men (4.35%) than in women (3.62%), with a male to female ratio of 1.19:1. No case of urolithiasis was found in subjects under the age of 20. In subjects over 19 years, the prevalence rate of the disease was 5.14%; 5.98% for men (CI 3.41-8.55%) and 4.49% for women (CI 2.61-6.37%). Prevalence increased with age, ranging from 2.75% in the 20-39 age group to 7.79% in those >or=60 years. The life time prevalence rate of urolithiasis observed in Buenos Aires is similar to that reported in a few other studies performed among males and females in the general population of USA and Europe. Prevalence of urolithiasis increases with age both in men and in women.

It is known that several metabolic abnormalities that favor stone formation have a strong dependence on environmental and nutritional factors. The incidence and prevalence of kidney stone is increasing while there has been a parallel growth in the overweight/obesity rate, and epidemiologic studies have shown a significant association between overweight/obesity and increased nephrolithiasis risk. The aim of this study was to assess if metabolic abnormalities observed in stone patients differ in relation to their BMI. We evaluated 817 renal stone formers (459 men and 358 woman) in an outpatient setting. They were all studied with a standard protocol (two 24 h urine collections and serum parameters) and classified according to their BMI in normal, overweight and obese and according to age in <50 or >50 year old. In the whole population we found that 58.7% were either overweight or obese: 39.4% (n = 322) were OW and 19.3% (n = 158) were OB. The proportion of overweight was significantly higher among men than women. In women of all ages regardless of BMI, hypercalciuria was the most prevalent diagnosis. Hyperuricosuria increased its prevalence significantly only in overweight and obese women <50 years of age (p < 0.01). Hypercalciuria was the predominant diagnosis in normal weight men of both age groups. Hyperuricosuria was the most frequent abnormality in overweight and obese men followed by gouty diathesis and both increased their prevalence significantly from normal weight to obesity and in both age groups (p < 0.05 and <0.01). We conclude that the only abnormalities that increased their prevalence significantly with increasing BMI were hyperuricosuria and gouty diathesis, the first one in men of all ages and women under 50 years of age, while the second one only in men.