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Abbreviation for cystometrogram.

cystometrography (CMG)

a urological procedure that measures the amount of pressure exerted on the bladder at various bladder volumes. The test helps determine bladder capacity, bladder wall compliance, detrusor stability, and sensations of filling. It is often done in conjunction with electromyography and other urodynamic tests.


A gene on chromosome Xp11.4 that encodes a calcium/calmodulin-dependent serine protein kinase of the membrane-associated guanylate kinase (MAGUK) family, which are scaffold proteins located at synapses in the brain. CASK is involved in synaptic transmembrane protein anchoring and ion channel trafficking; contributes to neural development and regulating gene expression by interacting with the transcription factor TRB1; binds to cell-surface proteins, including amyloid precursor protein, neurexins and syndecans; and may mediate a link between the extracellular matrix and the actin cytoskeleton with syndecan and the actin/spectrin-binding protein 4.1.
Molecular pathology
CASK mutations are associated with FG syndrome 4, mental retardation and microcephaly with pontine and cerebellar hypoplasia, as well as an X-linked form of mental retardation.


Synonym/acronym: CMG, urodynamic testing of bladder function.

Common use

To assess bladder function related to obstruction, neurogenic pathology, and infection including evaluation of surgical, and medical management.

Area of application

Bladder, urethra.




Cystometry evaluates the motor and sensory function of the bladder when incontinence is present or neurological bladder dysfunction is suspected and monitors the effects of treatment for the abnormalities. This manometric study measures the bladder pressure and volume characteristics in milliliters of water (cm H2O) during the filling and emptying phases. The test provides information about bladder structure and function that can lead to uninhibited bladder contractions, sensations of bladder fullness and need to void, and ability to inhibit voiding. These abnormalities cause incontinence and other impaired patterns of micturition. Cystometry can be performed with cystoscopy and electromyography pelvic floor sphincter.

A post-void residual measurement can also be done at the bedside to measure how much urine is left in the bladder after the patient voids. Completion of this test requires catheterization of the patient directly after voiding. The amount of urine remaining is measured and reported as the post-void or residual urine. Normal post-void residual is less than 50 mL of urine. This may be adjusted to less than 100 mL for those over the age of 65.

This procedure is contraindicated for

  • high alertPatients with acute urinary tract infections (UTIs) because the study can cause infection to spread to the kidneys.
  • high alertPatients with urethral obstruction.
  • high alertPatients who are unable to be catheterized.
  • high alertPatients with cervical cord lesions because they may exhibit autonomic dysreflexia, as seen by bradycardia, flushing, hypertension, diaphoresis, and headache.


  • Detect congenital urinary abnormalities
  • Determine cause of bladder dysfunction and pathology
  • Determine cause of recurrent urinary tract infections (UTIs)
  • Determine cause of urinary retention
  • Determine type of incontinence: functional (involuntary and unpredictable), reflex (involuntary when a specific volume is reached), stress (weak pelvic muscles), total (continuous and unpredictable), urge (involuntary when urgency is sensed), and psychological (e.g., dementia, confusion affecting awareness)
  • Determine type of neurogenic bladder (motor or sensory)
  • Evaluate the management of neurological bladder before surgical intervention
  • Evaluate postprostatectomy incontinence
  • Evaluate signs and symptoms of urinary elimination pattern dysfunction
  • Evaluate urinary obstruction in male patients experiencing urinary retention
  • Evaluate the usefulness of drug therapy on detrusor muscle function and tonicity and on internal and external sphincter function
  • Evaluate voiding disorders associated with spinal cord injury

Potential diagnosis

Normal findings

  • Amount of post-void residual urine is less than 50 mL
  • Normal sensory perception of bladder fullness, desire to void, and ability to inhibit urination; appropriate response to temperature (hot and cold)
  • Normal bladder capacity: 350 to 750 mL for men and 250 to 550 mL for women
  • Normal functioning bladder pressure: 8 to 15 cm H2O
  • Normal sensation of fullness: 40 to 100 cm H2O or 300 to 500 mL
  • Normal bladder pressure during voiding: 30 to 40 cm H2O
  • Normal detrusor pressure: less than 10 cm H2O
  • Normal urge to void: 150 to 450 mL
  • Normal filling pattern
  • Urethral pressure that is higher than bladder pressure, ensuring continence

Abnormal findings related to

  • Flaccid bladder that fills without contracting
  • Inability to perceive bladder fullness
  • Inability to initiate or maintain urination without applying external pressure
  • Sensory or motor paralysis of bladder indicated by reduced filling pressures
  • Total loss of conscious sensation and vesical control or uncontrollable micturition (incontinence)

Critical findings


Interfering factors

  • Factors that may impair the results of the examination

    • Inability of the patient to cooperate or remain still during the procedure because of age, significant pain, or mental status.
    • Inability of the patient to void in a supine position or straining to void during the study.
    • A high level of patient anxiety or embarrassment, which may interfere with the study, making it difficult to distinguish whether the results are due to stress or organic pathology.
    • Administration of drugs that affect bladder function, such as muscle relaxants or antihistamines.

Nursing Implications and Procedure


  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this procedure can assist in assessing bladder function.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex or medications that may be used during the procedure.
  • Obtain a history of the patient’s genitourinary system, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Record the date of the last menstrual period and determine the possibility of pregnancy in perimenopausal women.
  • Obtain a list of the patient’s current medications, including anticoagulants, aspirin and other salicylates, herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus). Note the last time and dose of medication taken.
  • Review the procedure with the patient. Address concerns about pain and explain that there may be moments of discomfort and some pain experienced during the test. Inform the patient that the procedure is performed in a special urology room or in a clinic setting by the health-care provider (HCP), with support staff, and takes approximately 30 to 45 min.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Instruct the patient to report pain, sweating, nausea, headache, and the urge to void during the study.
  • Note that there are no food, fluid, or medication restrictions unless by medical direction.
  • Make sure a written and informed consent has been signed prior to the procedure and before administering any medications.


  • Potential complications:
  • UTI related to use of a catheter

  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient.
  • Avoid the use of equipment containing latex if the patient has a history of allergic reaction to latex.
  • Have emergency equipment readily available.
  • Instruct the patient to change into the gown, robe, and foot coverings provided, but not to void.
  • Position the patient in a supine or lithotomy position on the examination table. If spinal cord injury is present, the patient can remain on a stretcher in a supine position and be draped appropriately.
  • Ask the patient to void. During voiding, note characteristics such as start time; force and continuity of the stream; volume voided; presence of dribbling, straining, or hesitancy; and stop time.
  • Instruct the patient to cooperate fully and to follow directions. Instruct the patient to remain still during the procedure.
  • A urinary catheter is inserted into the bladder under sterile conditions, and residual urine is measured and recorded. A test for sensory response to temperature is done by instilling 30 mL of room-temperature sterile water followed by 30 mL of warm sterile water. Sensations are assessed and recorded.
  • Fluid is removed from the bladder, and the catheter is connected to a cystometer that measures the pressure. Sterile normal saline, distilled water, or carbon dioxide gas is instilled in controlled amounts into the bladder. When the patient indicates the urge to void, the bladder is considered full. The patient is instructed to void, and urination amounts as well as start and stop times are then recorded.
  • Pressure and volume readings are recorded and graphed for response to heat, full bladder, urge to void, and ability to inhibit voiding. The patient is requested to void without straining, and pressures are taken and recorded during this activity.
  • After completion of voiding, the bladder is emptied of any other fluid, and the catheter is withdrawn, unless further testing is planned.
  • Further testing may be done to determine if abnormal bladder function is being caused by muscle incompetence or interruption in innervation; anticholinergic medication (e.g., atropine) or cholinergic medication (e.g., bethanechol [Urecholine]) can be injected and the study repeated in 20 or 30 min.


  • Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
  • Monitor fluid intake and urinary output for 24 hr after the procedure.
  • Monitor vital signs after the procedure every 15 min for 2 hr or as directed. Monitor intake and output at least every 8 hr. Elevated temperature may indicate infection. Notify the HCP if temperature is elevated. Protocols may vary among facilities.
  • Instruct the patient to immediately report symptoms such as fast heart rate, difficulty breathing, skin rash, itching, chest pain, persistent right shoulder pain, or abdominal pain. Immediately report symptoms to the appropriate HCP.
  • Inform the patient that he or she may experience burning or discomfort on urination for a few voidings after the procedure.
  • Persistent flank or suprapubic pain, fever, chills, blood in the urine, difficulty urinating, or change in urinary pattern must be reported immediately to the HCP.
  • Recognize anxiety related to test results. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be needed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include bladder cancer markers, calculus kidney stone panel, Chlamydia group antibody, CBC, CBC hematocrit, CBC hemoglobin, CT pelvis, culture urine, cytology urine, IVP, MRI pelvis, PT/INR, US pelvis, and UA.
  • Refer to the Genitourinary System table at the end of the book for related tests by body system.
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