Uroflowmetry — Flow Shapes & What They Mean
Uroflowmetry is the simplest urodynamic test — the shape of the curve, not just the peak number, hints at what kind of voiding problem you're dealing with.
The big picture
Uroflowmetry is the simplest urodynamic test — the patient voids into a funnel and a machine plots flow against time. Its value is that the shape of the curve, not just the peak number, hints at what kind of voiding problem you're dealing with. It can't, by itself, prove obstruction (that needs a pressure-flow study), but it's the cheap, non-invasive screen that points you in the right direction.
The framework: the key metrics (Qmax, voided volume, PVR), the characteristic curve shapes and what each suggests, and the crucial limitation.
Mechanism pathway
Tap any step to see why it happens.
Curve shapes — illustrated
Normal — bell-shaped
Rapid rise, high Qmax, smooth symmetric fall.
BPH / obstruction — low plateau
Slow rise to a low Qmax, prolonged and flat.
Urethral stricture — box-like
Flat, very constant — fixed narrow calibre caps flow.
Underactive / staccato — interrupted
Fluctuating, intermittent — straining, sphincter activity.
Diagnostic algorithm
Each step answers one question. Tap to expand.
Board traps
Valid study needs voided volume ≥150 mL.
Qmax is the key number but can't separate obstruction from a weak detrusor — that needs pressure-flow.
Bell-shaped = normal; low flat plateau = obstruction (BPH); box-like flat = stricture; interrupted/straining = underactive detrusor or dysfunctional voiding.
Average flow is less useful than Qmax for detecting outlet obstruction.
A stricture curve is typically flatter and more uniform than a BPH curve.