A renal (kidney) scan is a diagnostic procedure that uses nuclear medicine to examine the anatomy and functioning of your kidneys. A renal scan is also called a renal scintigraphy, renal imaging, or a renogram.
During this procedure, a radioactive material, called a radioisotope or radionuclide “tracer,” is injected into your vein. The radioisotope releases gamma rays, which a gamma camera or scanner can detect from outside the body.
The gamma camera scans the kidney area. It tracks the radioisotope and measures how it is processed by the kidneys. The camera also works together with a computer to create images. These images detail the structure and functioning of the kidneys, based on how they interact with the tracer.
Images from a renal scan can show structural and functional abnormalities, helping doctors to diagnose a kidney problem in its earlier stages—without invasive techniques or surgery.
A renal scan identifies problems that are interfering with normal kidney function. In healthy individuals, your two kidneys:
- remove urea, or liquid waste, from the blood by producing urine
- maintain a balance of chemicals, such as sodium and potassium, in the blood
- supply the hormone erythropoietin, which supports red blood cell growth
- control blood pressure by producing the hormone renin
- provide the hormone calcitriol, which supplies calcium in bones
Typically, a change in renal function begins gradually and without symptoms. In many cases, routine blood and urine tests show the first signs of reduced kidney function.
A renal scan can identify the cause of reduced kidney function. The cause may be a disease, obstruction, or injury to the kidneys.
More than one type of problem can be explored during the same procedure. A renal scan measures kidney function by monitoring the flow of the radioisotope and how efficiently it is absorbed and passed by your kidneys. It also shows abnormalities in the structure, size, or shape of your kidneys.
Renal scans can identify and evaluate:
- decreased blood flow to the kidneys
- renovascular hypertension (high blood pressure in the renal arteries)
- tumors or cysts
- kidney disease
- the success of kidney treatments
- rejection of a kidney transplant
A renal scan is an outpatient, or same-day, procedure. You will not have to stay at the hospital overnight. The scan will be performed in a hospital radiology department or a specially equipped medical office by a nuclear medicine technician. Depending on the reasons for your scan, testing may take between 45 minutes and three hours. If you are claustrophobic, talk to the technician beforehand, as the camera may pass close to your body.
A renal scan typically involves the following steps:
- Before your procedure, you will remove any clothing, jewelry, dentures, or metal items that could interfere with your scan.
- You may have to change into a hospital gown.
- You will then lie down on a scanning table.
- A technician may insert an intravenous (IV) line into a vein in your hand or arm.
- A radioisotope will be inserted into a vein in your arm. You may feel a quick, sharp poke with the injection.
- There may be a waiting period between the injection and the first scan to allow the radioisotope to be processed.
- When the scanner is placed over your kidneys, it will detect the gamma rays from the radioisotope and create images of the area. Since any movement can alter or blur the image, you must stay absolutely still when an image is being scanned.
- If your scan is related to high blood pressure, you may be given an angiotensin-converting enzyme (ACE) inhibitor—a high blood pressure medication—during testing. This allows for comparison of your kidneys before and after the medication is absorbed.
- If your scan is to detect kidney blockages, you may be given a diuretic (water pill) to promote the passage of urine through the kidneys. This allows your doctor to observe restrictions to urine flow.
- If an empty bladder is necessary, a catheter (soft tube) may be inserted to maintain this condition.
- When the scan is finished, the IV line and/or catheter will be removed.
- You can then change back into your clothing and leave the hospital.
- You can usually return to your regular diet and daily routine after your procedure, unless your doctor has advised you otherwise.
- The radioisotope will exit your body naturally. Frequent drinking of fluids and urinating can hasten this process.
Nuclear medicine imaging is considered safe. In fact, the radioisotope tracer exposes you to less radiation than an X-ray. The small amount of radiation exposure is primarily in the kidney area, and it passes from your body naturally within 24 hours.
The low doses of radiation used in nuclear medicine procedures are not related to any long-term negative effects.
Even though the radiation exposure is minimal and short-term, tell your physician if you are pregnant, or think you might be pregnant, to ensure that your fetus is not harmed. Also, tell your physician if you are breastfeeding to ensure that your milk will not be contaminated.
Unlike intravenous dyes, radioisotopes carry few risks of allergic reactions. Allergic reactions to radioisotopes, though possible, are rare. A renal scan is a good option if you have had a reaction to the contrast dye used in X-rays of the urinary system.
You may have discomfort, redness, bleeding, or swelling from the needle stick of the IV. If any of these symptoms persist, contact your physician, since they could indicate an infection.
Depending on your physical condition or whether you have had a recent surgery or injury, you may feel discomfort or pain from lying on the scanner table in a still position for a long period of time. You may also feel some degree of dizziness upon arising from the table. This dizziness and discomfort should only last a moment.
Typically, you do not need to make any special preparations before a renal scan. You usually can eat your normal diet without fasting. Sedation is not typically necessary.
You should tell your physician about any prescription or over-the-counter medications you are taking. Discuss how they should be used before and during the test.
Your physician may provide special instructions if you are taking medications that could affect the results of the renal scan. These medications include:
- diuretics (water pills)
- ACE inhibitors for heart conditions or high blood pressure
- beta-blockers for heart conditions or high blood pressure
nonsteroidal anti-inflammatory drugs (NSAIDs), including aspirin or ibuprofen
After the technician completes your renal scan, a nuclear medicine radiologist will interpret the images. A comprehensive report will then be sent to your physician, who will discuss the results with you.
Abnormal results of a renal scan can indicate:
- kidney disease
- the presence of cysts or tumors
- blockage of the renal arteries due to injury or trauma
- blockage that restricts the flow of urine from the kidneys to the bladder
- kidney inflammation caused by infection
- renovascular hypertension
- problems with a kidney transplant
- kidney failure
With some findings, your physician may require further testing to clarify a diagnosis. The results of your scan are calculated in relation to average kidney size and shape. If you have abnormal kidney structure, it could result in an incorrect reading, so further confirmation may be needed.
Also, since renal scans can’t identify the difference between a cyst and a tumor, additional diagnostic procedures may be required for a more definite diagnosis.