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

For a scan that looks at kidney appearance (cortical scan), the tracer used binds to the kidney long enough to get pictures of the kidney. After about 20 minutes, the gamma camera takes pictures of 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, scarring, or pockets of infection (abscesses).

Two types of kidney scans can be done:

• A cortical scan can be done to look at the shape of the kidneys.
• A functional 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 a picture of the tracer in the kidneys and bladder.

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.
• Evaluate 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).