Urinary supersaturation on fractioned urine collections: which urine sample can explain better the variability observed on 24-h urine? A proof-of-concept study.

Due to the difficulty of collecting 24-h urines in the stone-forming patient, some authors have suggested other types of urine collection, but their usefulness is not yet well studied. The objective of this study is to evaluate the variation of urinary supersaturation (SS) throughout the day and to analyze whether timed urine collections offer accurate information. 48 urine samples were collected from 12 young adults. Each 24-h urine was collected on 7 2-h urine fractions and a 10-h overnight sample. Solute concentrations and SS for calcium oxalate (CaOx), calcium phosphate (CaP), and uric acid (UA) were determined. Linear regression and relative importance of predictors were used to determine the percentage of R