Interpreting Urodynamic Studies for Lower Urinary Tract Function

Components of Urodynamic Testing

The American Urological Association recommends post-void residual (PVR) assessment to evaluate the possibility of significant bladder and/or outlet dysfunction, particularly important in patients with neurological conditions 3
Uroflowmetry provides information about voiding function; at least two flow rates should be obtained with volumes greater than 150 ml for reliability 4
Cystometry (CMG) evaluates bladder filling and storage function, identifying conditions like detrusor overactivity 3
Pressure-flow studies (PFS) assess the relationship between detrusor pressure and urine flow rate during voiding, crucial for diagnosing bladder outlet obstruction 5
Videourodynamic studies combine imaging with pressure measurements for comprehensive assessment 1

Identify detrusor overactivity (DO), characterized by involuntary detrusor contractions during filling 4 6
Note that absence of DO on a single study does not exclude it as a cause of symptoms 5 6

In men, obstruction is likely with the classic "high pressure-low flow" pattern 4
In women with elevated detrusor voiding pressure and low flow, consider obstruction, especially with new symptoms after surgery 5 4
Distinguish detrusor underactivity from obstruction by relating detrusor pressure at maximum flow to the maximum flow rate 4 6

For neurogenic bladder: Complex CMG and pressure flow studies are essential during initial evaluation and follow-up 3 5
For LUTS in men: PFS are recommended before invasive therapy when Qmax is >10 ml/second to confirm obstruction 4
For mixed incontinence: UDS helps determine the predominant component and guide treatment 5

Reproduce the patient's symptoms during testing for accurate diagnosis 1 2
Interpret findings in the context of global assessment, including examination, diaries, and PVR measurements 5 6
Formulate specific urodynamic questions before testing: what information is needed and which technique is most appropriate 1 7

Urodynamic findings alone may not precisely predict treatment outcomes 3
Consider risks of infection and, in spinal cord injury patients, autonomic dysreflexia 5 4
Recognize that each patient is unique, requiring individualized interpretation of results 8
Be aware that symptoms and physical findings often do not adequately predict the underlying pathophysiology 1 7