During filling cystometry, which measurement is primarily recorded?

• A. Urine protein
• B. Detrusor pressure during filling
• C. Urine osmolality
• D. Serum sodium

Answer: (B)

During filling cystometry, the focus is on how the bladder fills and how the detrusor muscle behaves as it stores urine. The most important data come from detrusor pressure during filling, which reflects the actual activity of the bladder muscle as it fills. By recording intravesical pressure and, when possible, subtracting abdominal pressure, clinicians derive the detrusor pressure (the pressure generated by the bladder wall itself). This reveals whether the detrusor remains quiet, contracts involuntarily, or how compliant the bladder is, all of which are key to diagnosing storage disorders and mechanisms of incontinence.

Urine protein, urine osmolality, and serum sodium don’t assess bladder storage or detrusor function; they relate to kidney function, urine composition, and blood chemistry, not the mechanics of filling the bladder.