Evaluation of 24-h urine collection quality in the Swiss Kidney Stone Cohort-NCCR Kidney.CH

Background Kidney stone affect one in ten adults in Switzerland. Diet plays a key role in the development and management of kidney stones. We collected data on the dietary habits of stone formers and controls using two consecutive 24-h dietary recalls and 24-h urine collections as well as blood chemistry. We explored the quality and completeness of 24-hour urine collections of participants prior to using 24-h urinary electrolytes and urea excretions as biomarkers of dietary intakes. Methods The Swiss Kidney Stone Cohort (SKSC) is a multicentric cohort of stone formers. A control group, free of kidney stone on CT-scan, was recruited in the general adult population. The SKSC includes 803 kidney stones formers and 207 controls (table 1). We evaluated the quality of the 24-h urine collection at baseline using urinary creatinine excretion (μmol/kg/24h). We also used a multiple linear regression model, including age, sex, BMI and linguistic region as covariates, to explore whether urinary volume and creatinine excretion differed between cases and controls. Results Of the 1882 urinary collections available, 631(33,5%) were outside the 10th-90th percentiles of the expected urinary creatinine excretion values. Mean 24-h urinary volume (day 1) was 1809±786ml (SKSC) and 2078±827ml (controls). After adjusting for age, sex, BMI and linguistic region, controls have a higher urinary volume than cases (+263±66ml, p <0.001). Swiss Germans have higher urinary volumes (+153±52ml, p <0.01). Adjusted mean 24-h urinary creatinine excretion (day 1) was similar in cases (164±52μmol/kg/24h) and controls (166±43μmol/kg/24h, p = 0.6). Conclusions The percentage of inadequate collections falls within a range previously described in the literature. Patients have lower 24-h urinary volume, but similar creatinine excretion than controls. Swiss Germans have higher urinary volumes. Further analysis will be conducted using 24-h urinary electrolytes (sodium, potassium) and urea excretions to assess the dietary intake of the participants. (Table Presented)