Test Overview
A kidney scan is a
nuclear scanning test that is done to check
kidney function or appearance.
During a
scan to look at kidney function, a
radioactive tracer substance is injected into a vein
in the arm and then travels through the bloodstream to the
kidneys. The tracer flows through the
blood vessels in the kidneys and then is excreted into the urine. A special
camera (gamma) takes pictures of the tracer in the kidneys. This helps show
cell activity and function in the kidneys.
Many different kinds of kidney scans can be done. The types of kidney scans include a scan that looks at how blood flows to and through the kidneys, a scan that looks at the shape and size of the kidneys, and a scan that looks at how urine is made and flows out of the kidneys. Sometimes a doctor will do multiple scans at one time (for example, a triple renal study). Different radioactive tracers are used depending on what kind of scan is being done.
Areas of the kidneys where the tracer shows up
in higher-than-normal amounts, such as in some types of cancer, result in
bright or "hot" spots in the pictures. Areas where the tracer does not show up
appear as dark or "cold" spots. Cold spots can mean narrowing or blockage
of the blood vessels, pockets of fluid (cysts), some
cancers, scarring, or pockets of infection (abscesses).
The amount of time it takes for the tracer to move through the kidney, collect in
the urine, and drain into the bladder can also be seen in a kidney scan. This may be done to see how well the kidneys are working.
A kidney scan may be done instead of a kidney X-ray test
called an
intravenous pyelogram (IVP) for people who are
allergic to the special dye (contrast material) used during the
IVP.
Why It Is Done
A kidney scan is done to:
- Check the blood flow through the kidneys.
Abnormal flow may mean narrowed renal arteries that can cause a type of high
blood pressure called renovascular hypertension.
- See how a
transplanted kidney is working.
- Check the extent of kidney
damage caused by an injury or infection.
- Find an obstruction in the kidney or
ureter, such as from a
kidney stone.
- Find growths in the kidneys
(rare).
How To Prepare
Before your kidney scan, tell your
doctor if:
- You are or might be pregnant.
- You
are breastfeeding. The radioactive tracer used in this test can get into
your breast milk. Do not breastfeed your baby for 2 days after this test.
During this time, you can give your baby breast milk you stored before the test,
or you can give formula. Discard the breast milk you pump for 2 days after the test.
- Within the past 4 days, you have had an
X-ray test using barium contrast material (such as a
barium enema) or have taken a medicine (such as
Pepto-Bismol) that contains bismuth. Barium and bismuth can interfere with test
results.
- You have had an X-ray test using contrast material in the
last 48 hours. X-ray tests with contrast material may include an intravenous
pyelogram (IVP) or abdominal
computed tomography (CT) scan.
You may be asked to drink 2 to 3 glasses of water right
before the scan.
You may be asked to sign a consent form.
Talk to your doctor about any concerns you have regarding the need
for the test, its risks, how it will be done, or what the results will mean. To
help you understand the importance of this test, fill out the
medical test information form(What is a PDF document?).
How It Is Done
A kidney scan is usually done by a
nuclear medicine technologist. The scan pictures are usually interpreted by a
radiologist or
nuclear medicine specialist.
Before the test
You will need
to remove any jewelry that might interfere with the scan. You may need to take
off all or most of your clothes, depending on which area is being examined (you
may be allowed to keep on your underwear if it does not interfere with the
test). You will be given a cloth or paper covering to use during the
test.
During the test
The technologist cleans the site on your arm where the
radioactive tracer will be injected. A small amount of the radioactive tracer
is then injected. Medicine to increase your urine output (a diuretic) may also
be injected. You may lie on your back on a table, stand, or sit upright. A
large scanning camera will be positioned closely above your belly
The camera
will scan for radiation right after the radioactive tracer is injected. Scans
may be taken every few minutes for about 30 minutes. More pictures may be taken 1 to 2 hours after the tracer was injected. The scans produce pictures
as the tracer moves through your kidneys. You may also be given medicine to
help the scans check for certain kidney functions.
A chart called
a renogram may be made using the information from the kidney scan by
plotting the movement of the tracer through the kidneys and recording it on a
graph. A series of chart recordings is then made based on the amount of tracer
uptake in the kidneys over a period of time. These recordings provide
information about different phases of blood flow and kidney function.
A kidney scan usually takes about 30 minutes to 1 hour.
You need to remain very still during each scan to avoid
blurring the pictures. The camera does not produce any radiation, so you are
not exposed to any more radiation while the scan is being done.
How It Feels
You may feel nothing at all from the
needle puncture when the tracer is injected, or you may feel a brief sting or
pinch as the needle goes through the skin. Otherwise, a kidney scan is usually
painless. You may find it hard to remain still during the scan. Ask for a
pillow or blanket to make yourself as comfortable as possible before the scan
begins.
The test may be uncomfortable if you are having kidney
pain. Try to relax by breathing slowly and deeply.
Risks
Allergic reactions to the radioactive
tracer are rare. Most of the tracer will be eliminated from your body (through
your urine or stool) within a day, so be sure to promptly flush the toilet and
thoroughly wash your hands with soap and water. The amount of radiation is so
small that it is not a risk for people to come in contact with you following
the test.
Occasionally, some soreness or swelling may develop at
the injection site. These symptoms can usually be relieved by applying moist,
warm compresses to your arm.
There is always a slight risk of
damage to cells or tissue from being exposed to any radiation, including the
low level of radiation released by the radioactive tracer used for this test.
Results
A kidney scan is a
nuclear scanning test that is done to check
kidney function or appearance. The results of a kidney
scan are usually available in 2 days.
Kidney scan| Normal: | The radioactive tracer flows evenly to and
through each kidney at the same time. The kidneys are working
normally. |
|---|
The tracer flows from the kidneys into the urine, which then drains into the
ureters and
bladder. This process occurs within a normal time
range. |
The kidneys take up the
radioactive tracer evenly. No "hot" spots or "cold" spots are seen. |
| Abnormal: | The kidneys are not normal in shape, size,
or location. |
|---|
The tracer does not flow evenly through the
kidneys, meaning narrowing of, blockage of, or damage to the blood vessels
or tissue in the kidneys. This may also mean poor kidney function. |
The tracer collects in
an area ("hot" spot) of a kidney. This might mean a tumor containing a
higher-than-normal number of blood vessels. |
An area of the kidney
does not take up the tracer ("cold" spot). This may mean an
abscess,
cyst, or scarring. |
The tracer does
not pass from the kidneys into the urine and then through the ureters to the
bladder. This can mean the movement of urine from the kidney is blocked. |
What Affects the Test
Reasons you may not be able to have the test or why the results may not be helpful include:
What To Think About
- Abnormal results from a kidney scan may be
further investigated by tests such as a kidney
biopsy,
ultrasound, intravenous pyelogram (IVP), or computed
tomography (CT) scan.
- Another type of scan
(radionuclide cystogram) may be done to determine whether urine is flowing
backward from the bladder into the ureters. To learn more, see the
topic
Cystourethrogram.
References
Other Works Consulted
- Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
- Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
- Pagana KD, Pagana TJ (2010). Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
Credits
ByHealthwise Staff
Primary Medical ReviewerAdam Husney, MD - Family Medicine
Specialist Medical ReviewerHoward Schaff, MD - Diagnostic Radiology
Current as ofOctober 14, 2016