A different way to study frequency volume charts in patients with nocturia

Background Nocturia results from a mismatch between bladder capacity and nocturnal urine production (NUP), which is determined with a frequency volume charts (FVC). Aim This is the first study that aimed to describe variations in nocturia severity and its associated factors by evaluating FVCs per single 24 h‐period. Methods This was a post‐hoc analysis of patients who completed a 72 h‐FVC in prospective, observational studies. The nocturnal polyuria index (NPi) was defined as the ratio of nocturnal and 24 h urine output. Subgroups were defined according to variations in nocturia frequency during the three 24 h‐periods of the FVC (fluctuating/consistent) and to the number of nocturia episodes during a single night (0/1/≥2). Results We analyzed 504 24 h‐FVC, collected by 168 subjects (58% female) with a median age of 60 (50‐68) years. Nocturia frequency fluctuated in 69 (41%) subjects. For the same number of nocturnal voids, we found no differences in NPi and maximum voided volume (MVV) between consistent and fluctuating nocturia frequency. Increasing numbers of nocturnal voids were associated with an increasing NPi in subjects with fluctuating nocturia, while for consistent nocturia, it was linked to an increase in NPi and a decrease in MVV. For both subjects with fluctuating and consistent nocturia, increasing nocturia severity was associated with increasing daytime fluid intake. Conclusion For the same number of nocturnal voids, bladder capacity, and NUP were similar between patients with consistent and fluctuating nocturia. An increasing number of nocturnal voids in subjects with fluctuating nocturia was linked to more NUP and more daytime fluid intake.