What Is a Renal Scan?
A renal scan involves the use of radioactive material to examine your kidneys and assess their function. A renal scan is also known as a renal scintigraphy, renal imaging, or a renogram.
During this procedure, a technician injects a radioactive material called a radioisotope into your vein. The radioisotope releases gamma rays. A gamma camera or scanner can detect gamma rays from outside your body.
The gamma camera scans the kidney area. It tracks the radioisotope and measures how the kidneys process it. The camera also works with a computer to create images. These images detail the structure and functioning of the kidneys based on how they interact with the radioisotope.
Images from a renal scan can show both structural and functional abnormalities. This helps doctors diagnose a kidney problem in its earlier stages without invasive techniques or surgery.
A renal scan identifies problems with kidney function. Normally, the 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 to bones
A change in renal function typically begins gradually and without symptoms. In many cases, routine blood and urine tests, such as what’s done on an annual physical, 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.
A renal scan can explore more than one type of problem during the same procedure. A renal scan measures kidney function by monitoring the flow of the radioisotope and how efficiently your kidneys absorb and pass it. 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, which is high blood pressure in the renal arteries
- tumors or cysts
- kidney disease
- the success of kidney treatments
- the rejection of a kidney transplant
Typically, you don’t need to make any special preparations before a renal scan. You can usually eat your normal diet. Sedation isn’t usually necessary.
You should tell your doctor about any prescription or over-the-counter medications you’re taking. Discuss how to use them before and during the test. Your doctor may provide special instructions if you’re taking medications that could affect the results of the renal scan. These medications include:
- diuretics, or 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
A renal scan is an outpatient, or same-day, procedure. You won’t have to stay at the hospital overnight. A nuclear medicine technician performs the scan. This is usually done in either in a hospital radiology department or a medical office with special equipment.
Depending on the reasons for your scan, testing may take between 45 minutes and three hours. Talk to the technician beforehand if you’re claustrophobic because the camera may pass close to your body.
Before your procedure, you’ll remove any of the following that could interfere with your scan:
- metal items
You may have to change into a hospital gown. You’ll then lie down on a scanning table.
A technician may insert an intravenous (IV) line into a vein in your hand or arm. The technician will then insert a radioisotope 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 your kidneys to process the radioisotope.
The scanner will detect the gamma rays from the radioisotope and create images of the area. Since any movement can alter or blur the image, you’ll need to stay still as the scanner creates an image.
If you need the scan because you have high blood pressure, you may receive a high blood pressure medication called an angiotensin converting enzyme (ACE) inhibitor during testing. This allows for comparison of your kidneys before and after the medication is absorbed.
If you’re having the scan to look for kidney blockages, you may receive a diuretic, or water pill, to promote the passage of urine through the kidneys. This allows your doctor to observe restrictions to urine flow.
If you need to have an empty bladder for the scan, you may need a soft tube called a catheter to maintain this condition.
The technician will remove the IV line and catheter after the scan. 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 advises you otherwise. The radioisotope will exit your body naturally. Frequently drinking fluids and urinating can hasten this process.
Nuclear medicine imaging is considered safe. The radioisotope exposes you to less radiation than an X-ray. The small amount of radiation exposure is primarily in the kidney area. It passes from your body naturally within 24 hours.
The low doses of radiation used in nuclear medicine procedures don’t have a connection to any long-term negative effects.
Even though the radiation exposure is minimal and short-term, tell your doctor if you’re pregnant or think you might be pregnant. Also, tell your doctor if you’re breastfeeding to ensure that there’s no contamination of your breast milk.
Unlike intravenous dyes, radioisotopes carry few risks of allergic reactions. Allergic reactions to radioisotopes are possible but rare. A renal scan is a good option if you’ve had a reaction to the contrast dye used in X-rays of the urinary system.
The needle stick for the IV may cause:
Contact your doctor if any of these symptoms persist. They could indicate an infection.
Depending on your physical condition or whether you 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 time. You may also feel dizzy when you get up from the table. This dizziness and discomfort should only last a moment.
After the technician completes your renal scan, a nuclear medicine radiologist will interpret the image findings. They’ll send a comprehensive report to your doctor. Your doctor will discuss the results with you.
Abnormal results of a renal scan can indicate:
- kidney disease
- the presence of cysts or tumors
- a blockage of the renal arteries due to injury or trauma
- a blockage that restricts the flow of urine from the kidneys to the bladder
- kidney inflammation due to infection
- renovascular hypertension
- problems with a kidney transplant
- kidney failure
Your doctor may require further testing to clarify a diagnosis. Your kidney size and shape influence the results of your scan. An abnormal kidney structure could result in an incorrect reading. Further confirmation may be necessary.
Also, because renal scans can’t identify the difference between a cyst and a tumor, additional diagnostic procedures may be necessary for a more definite diagnosis.