Which finding on evaluation would most support an overflow mechanism?

• A. Normal post-void residual with normal detrusor contraction.
• B. Elevated post-void residual with reduced detrusor contractility.
• C. Regular bladder emptying with detrusor overactivity.
• D. Normal residual and normal detrusor.

Answer: (B)

Overflow incontinence arises when the bladder can’t empty properly, leaving urine behind because the detrusor muscle isn’t generating enough pressure to complete voiding. The combination of an elevated post-void residual and reduced detrusor contractility perfectly fits this pattern: the bladder is not expelling urine effectively, so a large amount remains after voiding, and the detrusor’s weak contraction confirms the underactive bladder muscle rather than a purely mechanical blockage. This contrasts with a normal residual and normal detrusor, which indicates normal emptying; detrusor overactivity would typically cause urgency and urge incontinence with normal or even rapid emptying rather than leftover urine; and normal residual with normal detrusor is simply normal function.