Study protocol
A total of 65 persons signed an informed consent, 20 persons were excluded (never started (n = 17), night shift (n = 1), failed to follow the instructions for urine collections (n = 2)) and thus a total of 45 persons were eligible for analysis. Demographic data were collected.
Within a period of six weeks, two extended urine collections were obtained during two non-consecutive 24-hour periods to determine diuresis rate and renal functions. For this, participants were asked to collect 5 daytime 3 and nighttime urine samples at fixed time intervals over 24 hours. Voided volume at the time of sample collection, as well as volumes of any interim micturition, were recorded. During the first extended urine collection, participants also had to collect all daytime and nighttime urine in a daytime and nighttime container. Urinary concentration of osmolality, creatinine and sodium were determined for all urine samples and for both urine containers. Participants had to respect directives regarding the intake of fluids and food during both study days (drink 1.5-2 liters water and do not drink more than 2 units of alcohol per day; avoid salting their food and eating aperitif snacks, sauces, fast food and ready-made meals).
Furthermore, patients were asked to keep track of their movements and were requested to give an indication of what they had done the most during a period of time of one hour. Movement/position was divided into five categories. 0 was equivalent of having laid down the most that hour. 1 meant that the participant had been sat down for most of the hour. 2 stood for standing up. 3 was allocated to walking as the majority movement of the hour. 4 was given if the patient had performed more intense activity during that hour i.e. running, cycling etc.
The study was carried out in conformity with the Declaration of Helsinki. The Ghent University Hospital Review Board approved the study (EC/2013/802) and all participants gave written consent