Effectiveness of a voiding evaluation technique using a diaper equipped with a urination-activated alarm system to assess bladder function and voiding patterns in infants

Purpose Four-hour voiding observation is a conventional method for evaluating bladder function in infants. However, it requires a diaper check every 5 min during the observation period, which creates an unusual environment for the infant, making the evaluation of natural urination difficult. This study aimed to investigate the parameters of urination before mature bladder function using a diaper equipped with a urination-activated alarm system. Methods The study participants were 51 infants aged 0–4 years without bladder dysfunction. A urination-activated sensor was used to notify the inspector wirelessly when urination was detected, enabling the immediate assessment of ultrasonically measured residual urine. Bladder capacity was calculated as the sum of both residual urine volume and micturition volume, and the residual urine rate as the residual urine volume divided by bladder capacity. Results A total of 36 boys and 15 girls were enrolled. The median (interquartile range) residual urine volume, bladder capacity, and residual urine rate were 3.0 mL (1.1–6.6), 53.0 mL (33.9–75.3), and 7.0% (2.1–15.0), respectively. Infants aged 0–1 and 2–4 years were then classified into Group A ( N = 27) and Group B ( N = 24), respectively. The residual urine rate was significantly higher in Group A (11.0% [5.4–21.2]) than in Group B (4.8% [0.6–8.9]; p