Introduction: The causes of nocturia are often discussed separately as nocturnal urine volume and nocturnal bladder capacity problems. Since multiple factors affect nocturia, what affects it most has not been well investigated. We have been studying the bladder storage function as a homeostatic system keeps micturition interval constant by increasing the bladder capacity during the diuretic phase. We hypothesized that nocturnal diuresis could affect nocturnal urine volume and bladder storage function. This study aimed to identify the effect of nocturnal diuresis on bladder storage dysfunction for male patients with lower urinary tract symptoms (LUTS). Methods: Male LUTS patients who were able to keep 24-h frequency-volume charts (FVCs) for 3 days were included in this study. Patients with residual urine volume greater than 200 mL were excluded. Patients who marked an average of two or more times per night on 3-days 24h-FVCs were defined as the nocturia (+) group, and those who marked less than two times were defined as the nocturia (-) group. Patient characteristics and parameters of 24-h FVCs were compared between groups, with values of P<0.05 considered significant. Results: The nocturia (+) group (n=52) was significantly older (P=0.01), had a higher nocturnal diuresis rate (P <0.001), and had a smaller voided volume at night (P=0.01) than the nocturia (-) group (n=48). Multivariate analysis showed that increased nocturnal diuresis rate and decreased nocturnal voided volume were significantly related to nocturia (nocturnal diuresis rate: OR 1.04, P<0.001; decreased nocturnal single voided volume: OR 0.985, P=0.001). Nocturnal diuresis was defined as a ratio of the mean diuretic rate at night to the mean diuretic rate during the day of 0.83 or greater (AUC 0.87, sensitivity 81.1%, specificity 79.2%). 17.6% of patients had nocturia with nocturnal diuresis without nocturnal bladder storage dysfunction (nocturnal voided volume <229.3 mL). Then, they had a significantly higher nocturnal diuresis rate than patients with nocturnal diuresis and nocturnal bladder storage dysfunction (P=0.03). Conclusions: Nocturnal diuresis is clearly associated with nocturia, but an extreme increase in nocturnal diuresis rate unexpectedly leads to increased nocturnal urine volume. SOURCE OF Funding: Nothing
