Metabolic diagnosis in stone formers in relation to body mass index

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.