You will be asked to lie on the scanner table. The health care provider will place a tourniquet or blood pressure cuff on your upper arm, which creates pressure and enlarges your arm veins. The inner elbow is scrubbed with numbing medicine (antiseptic) and a small amount of radioisotope is injected into a vein. The specific radioisotope used may vary, depending on the kidney function that is being studied.
The pressure on the upper arm is released, which allows the radioactive material to travel through the bloodstream. The kidneys are scanned a short time later. Several images are taken, each lasting 1 or 2 seconds. The total scan time takes about 30 minutes to 1 hour.
A computer analyzes the images and provides detailed information about particular kidney functions (such as how much blood the kidney filters over time).
After the scan, no recovery time is required. You may be asked to drink plenty of fluids and urinate frequently to help remove the radioactive material from the body.
How to prepare for the test
Tell your health care provider if you take any nonsteroidal anti-inflammatory drugs (NSAIDs) or blood pressure medications, as they might interfere with the exam.
You may be asked to drink additional fluids before the scan.
You must sign a consent form.
You will be asked to wear a hospital gown. Remove jewelry, dentures, and metallic objects before the scan.
How the test will feel
There is a sharp prick when the isotope is injected into the vein. You will not feel the isotope. You should not feel the scan, although the table may be hard or cold. You will need to lie still during the scan.
Why the test is performed
A renal scan reveals the size, position, shape, and function of the kidneys. It is particularly useful when a person is sensitive or allergic to the contrast (dye) material used in an IVP or other x-rays, or when they have reduced kidney function.
There is a slight amount of radiation from the radioisotope. Most of this radiation exposure occurs to the kidneys and bladder as the isotope is removed from the body. Virtually all radiation is gone from the body in 24 hours. However, because of the slight exposure to radiation, caution is advised if you are pregnant or breastfeeding.
Problems with the kidney structure may lead to an inaccurate reading of the scans, since results are calculated based on normal kidney size and shape.
Louis S. Liou, MD, PhD, Chief of Urology, Cambridge Health Alliance, Visiting Assistant Professor of Surgery, Harvard Medical School. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.