What is the primary purpose of urodynamic testing, and what does filling cystometry measure during filling?

• A. Assess kidney function and urine flow.
• B. Measure urinary sediment and protein.
• C. Assess bladder sensation, capacity, detrusor activity, and closing pressures during filling.
• D. Evaluate external urethral sphincter strength only.

Answer: (C)

Urodynamic testing is about how the lower urinary tract stores urine and how the outlet behaves during filling and voiding, by recording pressures, volumes, and sensations. Filling cystometry specifically looks at the bladder’s storage function as it fills. It measures how the bladder senses filling (when first felt, when urge begins), the capacity it can hold, and how the bladder pressure rises as it fills (compliance). It also observes detrusor activity during filling—whether the bladder muscle remains quiet or contracts involuntarily. In addition, it assesses the closing pressures of the outlet during filling, which reflect urethral resistance and the ability to stay closed to prevent leakage.

That combination—bladder sensation, capacity, detrusor behavior, and outlet closing pressures during filling—best captures the purpose of filling cystometry within urodynamics. Other options either refer to tests outside this storage-function focus (kidney function and urine flow), address non-storage findings (urinary sediment or protein), or too narrowly target one aspect (sphincter strength only).