1143: Ethnic Background has Minimal Impact on the Etiology of Nephrolithiasis

Abstract

INTRODUCTION AND OBJECTIVE: Calcium oxalate stone formation is due to an interaction between environmental and genetic factors. Metabolic studies are undertaken for the study of both of these domains. These frequently involve placing patients on controlled diets. The appropriate length of lead-in time on these diets has not been adequately defined. We undertook this study to address this issue.METHODS: Eleven healthy, non-stone forming adults (5 men, 6 women, mean age 26.9 years) collected daily 24-hour urine collections while consuming a self-selected diet (SS) for 4 days and a controlled, metabolic diet (CM) for 10 consecutive days. The CM diet consisted of 20% protein, 30% fat, and 50% carbohydrate and contained 250 mg oxalate/2500 kcal and I 002 mg calcium/2500 kcal. The CM diet was adjusted to appropriate caloric requirements for each subject. The following urinary analytes were measured and indexed to urinary creatinine excretion: calcium, citrate, magnesium, oxalate, phosphate, potassium, sodium, urea nitrogen, and uric acid.RESULTS: There are statistically significant differences in oxalate, magnesium, potassium, sodium, and urea nitrogen excretion when comparing the SS diet to the CM diet. The coefficients of variability for calcium (p<O.Ol) and citrate (p<O.Ol) excretion on the CM diet was significantly less than on the SS diet. This also approached statistical significance for oxalate excretion. Rapid stabilization of urinary excretion of all metabolites occurs on the CM diet: equilibration on day I for calcium, citrate, magnesium, oxalate, phosphate, potassium, uric acid; equilibration on day 2 for sodium, urea nitrogen.CONCLUSIONS: Although undefined environmental and genetic factors influence the absorption and excretion of the major factors associated with calculogenesis, intraindividual variability in non-stone formers is low on a controlled diet, interindividual variability is present on a controlled diet which may represent genetic factors, and urinary stabilization is rapid. Lead-in times for metabolic studies using controlled diets can be limited in non-stone formers. Further similar investigations on stone formers need to be undertaken.