On this page:
Seeing Your Doctor or Nurse
Preparing for the Test
Taking the Test
After the Test
Getting the Results
For More Information
If you have a problem with urine leakage or blocked urine flow, your
doctor or nurse can help. One of the first steps may be urodynamic
testing to find precisely what the problem is.
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. Normal urine flow is
one way. If urine backs up toward the kidneys, infections are more
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 for 2 to 5 hours.
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
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
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
tighten, squeezing urine out. Urine can then leave the bladder through
the urethra. When these signals occur in the correct order, normal
Problems in the urinary system can be caused by aging, illness, or
injury. The muscles in your ureters, bladder, and urethra tend to
become weaker with age. You may have more urinary infections because
your bladder muscles have weakened and cannot empty your bladder
completely. Also, weakening of the muscles of the sphincters and the
pelvis can cause incontinence because the sphincter cannot remain
tight enough to hold urine in the bladder or does not have enough
support from the pelvic muscles.
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Urodynamics is the study of how the body stores and releases urine.
Urodynamic tests help your doctor or nurse see how well your bladder
and sphincter muscles work and can help explain symptoms such as
sudden, strong urges to urinate
problems starting a urine stream
problems emptying your bladder completely
recurrent urinary tract infections
These tests may involve imaging equipment that films urination or may
be as simple as urinating behind a curtain while a doctor or nurse
Seeing Your Doctor or Nurse
The first step in solving a urinary problem is to talk to 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
If leakage is the problem, a pad test is a simple way to measure how
much urine seeps 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 and then seal it in a 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, such as weakening pelvic muscles or prostate
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.
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
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 (postvoid
residual). Urodynamic tests can range from simple observation to
precise measurement using sophisticated instruments.
Uroflowmetry (Measurement of Urine Speed and Volume)
A uroflowmeter automatically measures the amount of urine and the flow
rate (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. 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 remove it with a catheter, a thin
tube that can be gently glided into the urethra. Ultrasound equipment
that uses harmless sound waves to create a picture of the bladder can
also be used. 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.
Cystometry (Measurement of Bladder Pressure)
Cystometry in a female patient
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 with a pressure-measuring tube called a cystometer
will be used to fill your bladder slowly with warm water. Another
catheter may be placed in the rectum to record pressure there as well.
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.
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 cystometer
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 try to exhale while holding your nose
and mouth to apply abdominal pressure to the bladder or cough or shift
positions. These actions help the doctor or nurse evaluate your
Pressure Flow Study
After the CMG, you will be asked to empty your bladder so that the
catheter can measure the pressures required to urinate. 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. Some 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 damage, you may be given an electromyography test. This test
measures the muscle activity in the urethral sphincter using sensors
placed on the skin near the urethra and rectum. Sometimes the sensors
are on the urethral or rectal catheter. Muscle activity is recorded on
a machine. The patterns of these impulses will show whether the
messages sent to the bladder and urethra are coordinated correctly.
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 liquid used to fill the bladder may be a contrast medium that will
show up on the x ray. The pictures and videos show the size and shape
of the urinary tract and help your doctor or nurse understand your
After the Test
You may have mild discomfort for a few hours after these tests.
Drinking two 8-ounce glasses of water each 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. Other tests may take a few days. You will
have the chance to ask questions about the results and possible
treatments for your problem.