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.
Why It Is Done
A kidney scan is done to:
How To Prepare
Before your kidney scan, tell your doctor if:
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
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.
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.
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
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