Nocturnal Polyuria - excess of nocturnal urine production, excess of definitions: influence on renal function profile

This study aims to identify important differences in renal function profile (RFP) and potential cutoff values for water and sodium diuresis among participants with nocturnal polyuria (NP) according to different NP definitions.

This post hoc analysis is based on a prospective study where participants were asked to complete a bladder diary, to collect urine for a renal function profile (RFP) (8 urine samples every 3 hours over 24h) and to provide a blood sample (osmolality and sodium concentrations). Four definitions of NP are compared with the age dependent NPindex (NPI)>20-33% as reference: NPI>33%, nocturnal urine production (NUP)>90ml/h, NUP>10ml/kg and nocturia index>1,5.

A total of 112 participants were included with a mean age of 57 years (SD 16), 41% were female. Significant differences in baseline characteristics and bladder diary parameters were found according to the different definitions. Diuresis rate, free water clearance and sodium clearance have similar courses over 24h for both the subgroup with and without NP based on each definition. The range shows a larger variation for the subgroup with NP compared to the subgroup without NP, especially at night for diuresis rate and FWC. At night, a decrease in FWC is seen for the subgroup with NP based on each definition (p90 and NPI>20-33 definitions. For each definition, sodium clearance remains high throughout the night in the subgroup with NP, which differs significantly from the subgroups without NP (p

There are important differences in age, gender and bladder diary parameters comparing participants with and without NP based on various definitions. Although the course of RFP indicating the underlying pathophysiologic mechanism of NP, does not seem to be influenced by the choice of definition, the sensitivity of cut off values for FWC and sodium clearance differs substantially. However, these results need to be confirmed in a larger homogeneous study sample.

The Journal of urology. 2015 Sep 24 [Epub ahead of print]

A Goessaert, J Vande Walle, J L H R Bosch, P Hoebeke, K Everaert

Urology Department, Ghent University Hospital, Belgium.  Pediatric Nephrology Department, Ghent University Hospital, Belgium. , Urology Department, University Medical Center Utrecht, Utrecht, The Netherlands. , Urology Department, Ghent University Hospital, Belgium. , Urology Department, Ghent University Hospital, Belgium.