Urodynamic 

Testing 

National Kidney and Urologic Diseases Information Clearinghouse 

National 

Institute of 

Diabetes and 

Digestive 

and Kidney 

Diseases 

NATIONAL 

INSTITUTES 

OF HEALTH 

U.S. Department 

of Health and 

Human Services 

If you have a problem with urine leakage or 

blocked urine flow, your doctor or nurse 

may be able to help. One of the tools they 

may use to evaluate the cause of your 

symptoms is urodynamic testing. 

Several muscles, organs, and nerves are 

involved in collecting, storing, and releasing 

urine. The kidneys form urine by filtering 

wastes and extra water from the bloodstream. The ureters are tubes that carry 

urine from the kidneys to the bladder. 

Normally urine flows in one direction. 

If urine backs up toward the kidneys, 

infections and kidney damage can occur. 

The bladder, a hollow muscular organ 

shaped like a balloon, sits in the pelvis and 

is held in place by ligaments attached to 

other organs and to the pelvic bones. The 

bladder stores urine until you are ready to 

empty it. It swells into a round shape 

when it is full and gets smaller as it empties. 

A healthy bladder can hold up to 16 ounces 

(2 cups) of urine comfortably. How frequently it fills depends on how much excess 

water your body is trying to get rid of. 

The bladder opens into the urethra, the 

tube that allows urine to pass outside the 

body. Circular muscles called sphincters 

close tightly to keep urine from leaking. 

The involuntary leakage of urine is called 

incontinence. 

Nerves in the bladder tell you when it is 

time to empty your bladder. When the 

bladder begins to fill with urine, you may 

notice a feeling that you need to urinate. 

The sensation becomes stronger as the 

bladder continues to fill and reaches its 

limit. At that point, nerves in the bladder 

send a message to the brain, and your urge 

to urinate intensifies. 

Kidneys 

Ureters 

Urine 

Urethra 

Bladder 

muscle 

Pelvic floor Sphincter 

muscles muscles 

Urinary tract. 

When you are ready to urinate, the brain 

signals the sphincter muscles to relax. At 

the same time, the brain signals the bladder 

muscles to squeeze, thus allowing urine to 

flow through the urethra. When these 

signals occur in the correct order, normal 

urination occurs. 

Problems in the urinary system can be 

caused by aging, illness, or injury. The 

muscles in and around your bladder and 

urethra tend to become weaker with age. 

Weak bladder muscles may result in your 
not being able to empty your bladder 

completely, leaving you at a higher risk for 

urinary tract infections. Weak muscles of 

the sphincters and pelvis can lead to urinary incontinence because the sphincter 

muscles cannot remain tight enough to hold 

urine in the bladder, or the bladder does 

not have enough support from the pelvic 

muscles to stay in its proper position. 

Urodynamics is a study that assesses how 

the bladder and urethra are performing 

their job of storing and releasing urine. 

Urodynamic tests help your doctor or 

nurse see how well your bladder and 

sphincter muscles work and can help 

explain symptoms such as 

•	 incontinence 

•	 frequent urination 

•	 sudden, strong urges to urinate 

•	 problems starting a urine stream 

•	 painful urination 

•	 problems emptying your bladder
 

completely 


•	 recurrent urinary tract infections 

These tests may be as simple as urinating 

behind a curtain while a doctor or nurse 

listens or more complicated, involving 

imaging equipment that films urination and 

pressure monitors that record the pressures 

of the bladder and urethra. 

Seeing Your Doctor 

or Nurse 

The first step in solving a urinary problem 

is to talk with your doctor or nurse. He or 

she should ask you about your general 

medical history, including any major illnesses or surgeries. You should talk about 

the medicines you take, both prescription 

and nonprescription, because they might be 

part of the problem. You should talk about 

how much fluid you drink a day and 

whether you use alcohol or caffeine. Give 

as many details as you can about the problem and when it started. The doctor or 

nurse may ask you to keep a voiding diary, 

which is a record of fluid intake and trips to 

the bathroom, plus any episodes of leakage. 

If leakage is the problem, the doctor or 

nurse may ask you to do a pad test. This 

test is a simple way to measure how much 

urine leaks out. You will be given a number 

of absorbent pads and plastic bags of a 

standard weight. You will be told to wear 

the pad for 1 or 2 hours while in the clinic 

or to wear a series of pads at home during 

a specific period of time. The pads are 

collected and sealed in a plastic bag. Your 

health care team will then weigh the bags 

to see how much urine has been caught in 

the pad. A simpler but less precise method 

is to change pads as often as you need to 

and keep track of how many pads you use 

in a day. 

A physical exam will also be performed to 

rule out other causes of urinary problems. 

This exam usually includes an assessment 

of the nerves in the lower part of your body. 

It will also include a pelvic exam in women 

to assess the pelvic muscles and the other 

pelvic organs. In men, a rectal exam is 

given to assess the prostate. Your doctor 

will also want to check your urine for evidence of infection or blood. 

Preparing for the Test 

If the doctor or nurse recommends bladder 

testing, usually no special preparations are 

needed, but make sure you understand any 

instructions you do receive. Depending 

on the test, you may be asked to come 

with a full bladder or an empty one. Also, 

ask whether you should change your diet 

or skip your regular medicines and for 

how long. 

2	 Urodynamic Testing 
Taking the Test 

Any procedure designed to provide information about a bladder problem can be 

called a urodynamic test. The type of test 

you take depends on your problem. 

Most urodynamic testing focuses on the 

bladder’s ability to empty steadily and 

completely. It can also show whether the 

bladder is having abnormal contractions 

that cause leakage. Your doctor will want 

to know whether you have difficulty starting 

a urine stream, how hard you have to strain 

to maintain it, whether the stream is interrupted, and whether any urine is left in 

your bladder when you are done. The 

remaining urine is called the postvoid residual. Urodynamic tests can range from simple observation to precise measurement 

using sophisticated instruments. 

Uroflowmeter equipment. 

Uroflowmetry (Measurement of 

Urine Speed and Volume) 

A uroflowmeter automatically measures 

the amount of urine and the flow rate— 

that is, how fast the urine comes out. You 

may be asked to urinate privately into a 

toilet that contains a collection device and 

scale. This equipment creates a graph that 

shows changes in flow rate from second to 

second so the doctor or nurse can see the 

peak flow rate and how many seconds it 

took to get there. Results of this test will 

be abnormal if the bladder muscle is weak 

or urine flow is obstructed. 

Your doctor or nurse can also get some 

idea of your bladder function by using a 

stopwatch to time you as you urinate into a 

graduated container. The volume of urine 

is divided by the time to see what your 

average flow rate is. For example, 330 

milliliters (mL) of urine in 30 seconds 

means that your average flow rate is 11 mL 

per second. 

Measurement of Postvoid 

Residual 

After you have finished, you may still have 

some urine, usually only an ounce or two, 

remaining in your bladder. To measure this 

postvoid residual, the doctor or nurse may 

use a catheter, a thin tube that can be gently glided into the urethra. He or she can 

also measure the postvoid residual with 

ultrasound equipment that uses harmless 

sound waves to create a picture of the bladder. A postvoid residual of more than 200 

mL, about half a pint, is a clear sign of a 

problem. Even 100 mL, about half a cup, 

requires further evaluation. However, the 

amount of postvoid residual can be different each time you urinate. 

3 Urodynamic Testing 
Cystometry (Measurement of 

Bladder Pressure) 

A cystometrogram (CMG) measures how 

much your bladder can hold, how much 

pressure builds up inside your bladder as it 

stores urine, and how full it is when you 

feel the urge to urinate. The doctor or 

nurse will use a catheter to empty your 

bladder completely. Then a special, 

smaller catheter will be placed in the 

bladder. This catheter has a pressuremeasuring device called a manometer. 

Another catheter may be placed in the 

rectum to record pressure there as well. 

Your bladder will be filled slowly with warm 

water. During this time you will be asked 

how your bladder feels and when you feel 

the need to urinate. The volume of water 

and the bladder pressure will be recorded. 

You may be asked to cough or strain during 

this procedure. Involuntary bladder contractions can be identified. 

Bladder 

Catheter 

Urethra 

Cystometry in a female patient. 

Measurement of Leak Point 

Pressure 

While your bladder is being filled for the 

CMG, it may suddenly contract and 

squeeze some water out without warning. 

The manometer will record the pressure at 

the point when the leakage occurred. This 

reading may provide information about the 

kind of bladder problem you have. You 

may also be asked to apply abdominal pressure to the bladder by coughing, shifting 

position, or trying to exhale while holding 

your nose and mouth. These actions help 

the doctor or nurse evaluate your sphincter 

muscles. 

Pressure Flow Study 

After the CMG, you will be asked to empty 

your bladder. The catheter can measure 

the bladder pressures required to urinate 

and the flow rate a given pressure generates. This pressure flow study helps to 

identify bladder outlet obstruction that men 

may experience with prostate enlargement. 

Bladder outlet obstruction is less common 

in women but can occur with a fallen bladder or rarely after a surgical procedure for 

urinary incontinence. Most catheters can 

be used for both CMG and pressure flow 

studies. 

Electromyography 

(Measurement of Nerve 

Impulses) 

If your doctor or nurse thinks that your 

urinary problem is related to nerve or 

muscle damage, you may be given an 

electromyography. This test measures the 

muscle activity in and around the urethral 

sphincter by using special sensors. The 

sensors are placed on the skin near the 

urethra and rectum or they are located on 

4 Urodynamic Testing 
the urethral or rectal catheter. Muscle

activity is recorded on a machine. The patterns of the impulses will show whether the

messages sent to the bladder and urethra

are coordinated correctly.

Video Urodynamics

Urodynamic tests may be performed with

or without equipment to take pictures of

the bladder during filling and emptying.

The imaging equipment may use x rays or

sound waves. If x-ray equipment is used,

the bladder will be filled with a contrast

medium that will show up on the x ray

instead of the warm water. The pictures

and videos show the size and shape of the

urinary tract and help your doctor or nurse

understand your problem.

After the Test

You may have mild discomfort for a few

hours after these tests when you urinate.

Drinking an 8-ounce glass of water each

half-hour for 2 hours should help. Ask

your doctor whether you can take a warm

bath. If not, you may be able to hold a

warm, damp washcloth over the urethral

opening to relieve the discomfort.

Your doctor may give you an antibiotic to

take for 1 or 2 days to prevent an infection.

If you have signs of infection—including

pain, chills, or fever—call your doctor at

once.

Getting the Results

Results for simple tests can be discussed

with your doctor or nurse immediately after

the test. Results of other tests may take a

few days. You will have the chance to ask

questions about the results and possible

treatments for your problem.

For More Information

More information is available from

American Urological Association

Foundation

1000 Corporate Boulevard

Suite 410

Linthicum, MD 21090

Phone: 1–866–RING–AUA (746–4282) 

or 410–689–3700

Email: patienteducation@auafoundation.org

auafoundation@auafoundation.org

Internet: www.auafoundation.org

www.urologyhealth.org

Interstitial Cystitis Association of America

110 North Washington Street

Suite 340

Rockville, MD 20850–2223

Phone: 1–800–HELP–ICA (435–7422) 

or 301–610–5300

Email: icamail@ichelp.org

Internet: www.ichelp.org

5 Urodynamic Testing

You may also find additional information

about this topic by visiting MedlinePlus at

www.medlineplus.gov.
National Kidney and 

Urologic Diseases 

Information Clearinghouse 

3 Information Way 

Bethesda, MD 20892–3580 

Phone: 1–800–891–5390 

Fax: 703–738–4929 

Email: nkudic@info.niddk.nih.gov 

Internet: www.kidney.niddk.nih.gov 

The National Kidney and Urologic Diseases 

Information Clearinghouse (NKUDIC) is a 

service of the National Institute of Diabetes 

and Digestive and Kidney Diseases (NIDDK). 

The NIDDK is part of the National Institutes 

of Health of the U.S. Department of Health 

and Human Services. Established in 1987, 

the Clearinghouse provides information about 

diseases of the kidneys and urologic system to 

people with kidney and urologic disorders and 

to their families, health care professionals, and 

the public. The NKUDIC answers inquiries, 

develops and distributes publications, and 

works closely with professional and patient 

organizations and Government agencies to 

coordinate resources about kidney and urologic 

diseases. 

Publications produced by the Clearinghouse are 

carefully reviewed by both NIDDK scientists 

and outside experts. This fact sheet was 

reviewed by Michael Albo, M.D., University of 

California, San Diego, Medical School; and 

Holly E. Richter, Ph.D., M.D., University of 

Alabama at Birmingham School of Medicine. 

This publication is not copyrighted. The 

Clearinghouse encourages users of this fact 

sheet to duplicate and distribute as many 

copies as desired. 

This fact sheet is also available at 

www.kidney.niddk.nih.gov. 

U.S. DEPARTMENT OF HEALTH 

AND HUMAN SERVICES 

National Institutes of Health 

NIH Publication No. 07–5106 

November 2006