Abstract
OBJECTIVE: To explore why older men awaken to urinate within 3 h after falling asleep, we examined diuretic and urine storage states associated with the first void after falling asleep. METHODS: We enrolled 102 male patients, 50 years or older, hospitalized for prostate biopsy between November 2021 and September 2023. Patients were grouped based on their first undisturbed sleep period (FUSP): FUSP < 3 h or FUSP ≥ 3 h. A 24-h frequency-volume chart (FVC) was recorded. Urinary sodium, creatinine, and osmolality were measured from the first urine after sleep and upon waking. Free water clearance (FWC) and sodium clearance (SC) of the first urine after sleep were recorded. The urine storage state was calculated as the ratio of urine volume at first nocturnal voiding to the maximum voided volume (VV) according to 24-h FVC. RESULTS: Overall, 86 cases were analyzed. FWC was elevated in the first urine after sleep. It was significantly higher in the FUSP < 3 h group (p = 0.041). SC was elevated in the FUSP < 3 h group for both the first urine after sleep and the urine upon waking. The urine storage state tended to be lower in the FUSP < 3 h group (p = 0.057). Multivariate analysis revealed that FWC, SC, and the urine storage state independently associated with FUSP < 3 h. CONCLUSION: Decreased urine storage function, increased water diuresis, and increased sodium diuresis in the first urine after sleep are independent factors associated with FUSP < 3 h. Management of these factors may improve nocturia. TRIAL REGISTRATION: Institutional Review Board Certification Number: 679.