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Basic or extended urine sampling to analyse urine production?

Denys M.A. et. al.

Neurourology and Urodynamics 2017 Jan 5. doi: 10.1002/nau.23198.

Commentary by Philip Van Kerrebroeck

Frequency volume charts are valuable tools to objectify urine production in patients with nocturia, enuresis or nocturnal incontinence. However to elucidate underlying mechanism of (ab)normal urine production additional evaluations are necessary. In this respect analyses of daytime and night-time urine (=basic collection) or analyses of urine samples collected every 3 h (=extended collection) may extend this evaluation by describing circadian patterns of water and solute diuresis (=renal function profiles). In this study the authors aimed to assess intra-individual correlation and agreement between renal function profiles provided using basic and extended urine collections, and using two extended urine collections. The final goal was to  create a short-form of the extended collection. A prospective observational study was executed at Ghent University Hospital in Belgium, and study participation was open for anyone visiting the hospital. Participants collected one basic and two extended 24-h urine collections, and urinary levels of osmolality, sodium and creatinine were determined. A moderate to strong correlation between results of basic and extended urinalyses was found. Comparing both extended urinalyses indicated a moderate correlation between the eight individual samples and a weak to strong correlation between the mean daytime and night-time values of renal functions. Different samples could be considered as most representative for mean daytime values, while all samples collected between 03 and 05 am showed the highest agreement with mean night-time values of renal function. The authors conclude that since there is a good correlation and agreement between basic and extended urine collections to study the mechanisms underlying urine production, the choice of urine sampling method to evaluate urine production depends on the purpose. Therfore they propose that a night-time-only urine sample collected between 03 and 05 am may be the most practical approach.