Urinary supersaturation on fractioned urine collections: which urine sample can explain better the variability observed
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ORIGINAL PAPER
Urinary supersaturation on fractioned urine collections: which urine sample can explain better the variability observed on 24‑h urine? A proof‑of‑concept study Adrian Rodriguez1,2 · Rocco Baccaro1,2 · Giovanni Gambaro3 · Pietro Manuel Ferraro1,2 Received: 15 October 2019 / Accepted: 13 January 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract 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 2 attributed to each timed collection (individual SS). 43 24-h urine samples were included in the study. The highest SS values were: for CaOx, night period and first morning urine; for CaP, between 2 and 6 pm and at night; for UA, between 8 am and 12 pm. For CaOx, the SS from the samples between 8 pm and 8 am accounted for more than 40% of the R2; for CaP, the results were more equally distributed throughout the day, and for UA, the SS values from 12 to 4 pm accounted for more than 45% of the observed variability. In conclusion, urinary SS varies throughout the day, being higher for CaOx and CaP at night, and in the early morning for UA. For CaOx and UA, the overnight and 12–4 pm urine samples, respectively, contribute most to the variability observed in the SS of 24-h urine. Keywords Calcium phosphate · Calcium oxalate · Nephrolithiasis · Uric acid · Urinary supersaturation
Introduction The analysis of 24-h urine is considered the gold standard to diagnose urinary metabolic abnormalities in the stoneforming patient. In fact, the European and American Clinical Guidelines, as well as a consensus of experts, recommend the analysis of two consecutive 24-h urine in the high-risk * Pietro Manuel Ferraro [email protected] Rocco Baccaro [email protected] Giovanni Gambaro [email protected] 1
U.O.C. Nefrologia, Fondazione Policlinico Universitario A. Gemelli IRCCS, Via G. Moscati 31, 00168 Roma, Italia
2
Università Cattolica del Sacro Cuore, Roma, Italia
3
Renal Unit, Division of Nephrology and Dialysis, Department of Medicine, University of Verona, Verona, Italy
stone-forming patients [1-3]. In the majority of stone-forming patients, some metabolic abnormalities can be discovered. It is assumed that those abnormalities induce supersaturation for some crystal species, the sine qua non-condition for crystallization, and stone formation. The rationale behind Clinical Guidelines on Nephrolit
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