Differential Nocturnal Diuresis Rates Among Patients with and Without Nocturnal Polyuria Syndrome

Abstract

BackgroundThe mechanism of nocturnal polyuria (NP), a leading cause of nocturia, is poorly understood. ObjectiveTo characterize NP in terms of diuresis rate changes before and after the first nocturnal awakening. Design, setting, and participantsA frequency-volume chart (FVC) database of 773 entries from 440 veterans treated at a Veterans Affairs urology clinic was analyzed. The first FVCs completed by male patients aged ≥18 years with two or more nocturnal voids were included. Patients were excluded if they were taking diuretics or had sleep apnea, heart failure, edema, kidney disease, or diabetes insipidus. The 130 included individuals were divided into two cohorts: patients with NP and patients below this threshold. Analyses were performed using two different cutoffs for NP: nocturnal urine production (NUP) >90ml/h and nocturnal polyuria index (NPi) >0.33. Outcome measurements and statistical analysisWe compared “early nocturnal diuresis rate” (ENDR; first nocturnal voided volume/length of first uninterrupted sleep period), “late nocturnal diuresis rate” (LNDR; remaining nocturnal urine volume/remaining hours of sleep), and diurnal diuresis rate (daytime urine volume/hours awake) in patients with the nocturnal polyuria syndrome (NPS). Results and limitationsWithin groups, there were significant differences between ENDR and LNDR for NPS patients at NUP >90ml/h (152 vs 120ml/h, p=0.02) and NPi >0.33 (120 vs 91ml/h, p=0.02) but not for those without NPS at NUP ≤90ml/h (60 vs 59ml/h, p=0.29) or NPi ≤0.33 (75 vs 75ml/h, p=0.25). Limitations include retrospective design, single institution participation, and small sample size. ConclusionsThere exists a significant drop-off in nocturnal diuresis rate after the time of first awakening that is unique to patients with NPS. The large volume of urine produced in the early hours of sleep may provide the specific substrate for short-acting antidiuretics approved for use in patients with nocturia owing to NPS. Patient summaryWe analyzed adult males diagnosed with nocturnal polyuria syndrome to determine how their rate of urine production changed throughout the night. Our finding that these individuals produce urine at the highest rate in the early hours of sleep suggests that they may benefit from pharmaceuticals specifically designed to reduce urine production during this period.