Urodynamic Testing
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 likely.
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 intensifies.
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 urination
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 in 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.
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
frequent urination
sudden, strong urges to urinate
Urinary tract
problems starting a urine stream
painful urination
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 listens.
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 leakage.
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 enlargement.
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 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 (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. 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 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)
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
Uroflowmeter equipment
Cystometry in a female patient
abdominal pressure to the bladder or cough or shift positions. 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 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. 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 the
impulses will show whether the messages sent to the bladder and urethra are coordinated
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 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 problem.
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
Your doctor may give you an antibiotic to take for 1 or 2 days to prevent an infection. If you have
signs of infectionincluding pain, chills, or fevercall 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.