This chapter discusses the tests of urethral function. The International Continence Society (ICS) has suggested standardisation of the performance of the urethral function and defined parameters for measurements. Two tests may be included to assess urethral function specifically during filling cystometry: vesical or detrusor leak-point pressure estimation and abdominal leak-point pressure (ALPP). Tests of urethral function during voiding cystometry measure the relationship between pressure in the bladder and urine flow rate. Urethral pressure profilometry (UPP) provides a graph indicating the intraluminal pressure along the length of the urethra. Urethral retro-resistance pressure (URP) has been defined as the pressure required to achieve and maintain an open urethral sphincter. Urethral pressure reflectometry (UPR) is measured using a 5-mm diameter polyurethane bag and urethral transducer. Tests of urethral function may also be useful in identifying incompetent urethral closure mechanisms before obstructive surgery for stress urinary incontinence.

Cystometry is the measurement of pressures inside the bladder both during the storage phase and the voiding phase of urodynamics. Post-void residual urine is assessed prior to cystometry by a dedicated bladder scanner, conventional ultrasound scanner or via inserting and draining the residual urine through the urethral filling catheter. Cystometry is usually postponed if the patient has a urinary tract infection because this could influence the urodynamic findings. The bladder diary provides a good idea of the patient's normal functional bladder capacity, and is helpful in conducting the cystometrogram. Detrusor overactivity describes involuntary detrusor contractions occurring during the filling phase of cystometry. The International Continence Society defines urodynamic stress incontinence as urinary leakage seen during filling cystometry in the presence of raised abdominal pressure but in the absence of a detrusor contraction. Leakage seen during coughing while the cystometric trace shows no evidence of a detrusor contraction confirms the diagnosis.

Ambulatory urodynamic monitoring (AUM), using micro-tip pressure transducers and a digital solid-state recorder, is a useful additional test for women in whom conventional urodynamics fails to reproduce or explain the lower urinary tract symptoms of which they complain. This system allows information to be recorded digitally, downloaded and reviewed at the end of the test. AUM is performed in accordance with the International Continence Society (ICS) Standardisation of Ambulatory Urodynamic Monitoring. The care and observation of a patient undergoing AUM is as important in the diagnosis as the objective measurements and neither should be carried out in isolation. Checks on signal quality are highly important at the start, during the test and again before the test terminates. AUM has a role in monitoring voiding function. It allows women to pass urine in a flowmeter in a private setting as and when they desire.