Kidney Scan

Test Overview

A kidney scan is a nuclear scanning test that is done to evaluate kidney function.

During a kidney scan, 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. A special camera (gamma) takes pictures of the tracer in the kidneys. This helps show cell activity and function in the kidneys. 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 indicate narrowing or blockage of the blood vessels, pockets of fluid (cysts), some cancers, or pockets of infection (abscesses).

Two types of kidney scans can be done:

• A perfusion study can be done to evaluate the blood flow through the kidneys.
• A function study can be done to measure the amount of time it takes for the tracer to move through the kidney, collect in the urine, and drain into the bladder. See an illustration of the tracer in the kidneys and bladder.

These two types of kidney scans are often done at the same time.

A kidney scan may be done for people who are allergic to the special dye (contrast material) used for the kidney X-ray test called an intravenous pyelogram (IVP).

Why It Is Done

A kidney scan is done to:

• Check the blood flow through the kidneys. normal 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.
• Evaluate the extent of kidney damage caused by an injury.
• Detect an obstruction in the kidney or ureter, such as from a kidney stone.
• Detect growths in the kidneys (rare).

How To Prepare

Before your kidney scan, tell your doctor if:

• You are or might be pregnant.
• You are breast-feeding. Use formula (discard your breast milk) for 1 to 2 days after the scan until the radioactive tracer has been eliminated from your body.
• You are taking any medications, especially blood pressure or heart medications.
• 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 medication (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 before the test. 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.

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.

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. Medication 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 abdomen. After the radioactive tracer is injected, the camera will scan for radiation released by the tracer and produce pictures as the tracer moves through your kidneys.

You need to lie very still during each scan to avoid blurring the pictures. The camera does not produce any radiation, so you are not exposed to any additional radiation while the scan is being done.

For the kidney function study, a different tracer may be injected and a series of pictures will be taken every few minutes for 30 minutes. These images monitor flow of the tracer through the kidneys, into the ureters and, finally, into the bladder. As each picture is being taken, you must lie completely still. Occasionally, scans may be done while you are sitting upright or standing. In some studies, other medications such as captopril or a diuretic, may be given to help assess specific functions of the kidneys.

A chart called a renogram may be made using the information from the perfusion study scans 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. Another type of scan, called a static scan, also may be done several hours after a tracer is injected.

The kidney scan usually takes about 1 to 2 hours but can last up to 4 to 5 hours depending on what functions are being studied.

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 difficult 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 evaluate kidney function. The results of a kidney scan are usually available in 2 days.

What Affects the Test

Factors that can interfere with your test and the accuracy of the results include:

• Pregnancy. A kidney scan is not usually done during pregnancy because the radiation could damage the developing baby (fetus).
• Medications to control high blood pressure (antihypertensives).
• Barium and bismuth. If a kidney scan is needed, it should be done before any tests that use barium (such as a barium enema).
• kidney failure.
• An intravenous pyelogram (IVP) or abdominal computed tomography (CT) scan within 24 hours of a kidney scan. The contrast material used in these scans may affect kidney function.
• The inability to remain still during the test.

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. For more information, see the medical tests Kidney Biopsy, Abdominal Ultrasound, Intravenous Pyelogram (IVP), or CT Scan of the Body.
• Another type of scan (radionuclide cystogram) may be done to determine whether urine is flowing backward from the bladder into the ureters. For more information, see the medical test Cystourethrogram.