First voided volume: A novel approach to characterize nocturia

Area of Science:

• Urology
• Nephrology
• Sleep Medicine

Background:

• Nocturnal polyuria syndrome (NPS) is defined as nocturnal polyuria (NP) without clear causes.
• Assessing nocturnal urine production (NUP) trajectories can help differentiate NP patients with and without NPS.
• Absolute urine volume changes, crucial for interventions, are not well-characterized in NPS.

Purpose of the Study:

• To compare the ratio of the first nocturnal voided volume (FNVV) to the nocturnal average voided volume (NAVV) in patients with and without NPS.
• To evaluate the nocturnal urine trajectory ratio (NUTR) as a potential diagnostic marker for NPS.

Main Methods:

• Secondary analysis of 24-hour voiding diaries from adult male patients with NP.
• Patients were categorized based on NUP (≥90 ml/h) or nocturnal polyuria index (NPi; ≥0.33).
• Exclusion criteria included diabetes insipidus and CPAP-adherent obstructive sleep apnea (OSA); secondary NP causes (OSA, CHF, CKD) were excluded from the NPS group.

Main Results:

• At NUP ≥90 ml/h, NUTR was significantly higher in patients with NPS (n=73) compared to those without (n=28) (1.10 vs. 0.91, p=0.012).
• At NPi ≥0.33, NUTR was also significantly greater in patients with NPS (n=92) versus without (n=32) (1.09 vs. 0.91, p=0.010).

Conclusions:

• The ratio of early to average nocturnal urine volume (NUTR) is significantly elevated in patients with NPS.
• Early nocturnal urine volume is key for identifying NPS in patients experiencing nocturia.