What is a computed tomography (CT) scan of the kidney?

CT scan is a type of imaging test. It uses X-rays and computer technology to make images or "slices" of the body. A CT scan can make detailed pictures of any part of the body. This includes the bones, muscles, fat, organs, and blood vessels. They are more detailed than regular X-rays.

In a CT scan, an X-ray beam moves in a circle around your body. This allows many different views of the same part of the body. The X-ray information is sent to a computer that interprets the X-ray data and displays it on a monitor.

During some tests, you may get contrast dye orally or through a vein. This will make parts of your body show up better in the image.

CT scans of the kidneys can give more detailed information about the kidneys than standard X-rays. This can provide more information related to injuries or diseases of the kidneys. CT scans of the kidneys can help your healthcare provider find problems, such as tumors or other lesions, obstructive conditions, such as kidney stones, congenital anomalies, polycystic kidney disease, buildup of fluid around the kidneys, and the location of abscesses.

Your healthcare provider may need to do other related tests to diagnose kidney problems.

Why might I need a CT scan of the kidney?

A CT scan of the kidney may be done to check the kidneys for:

• Tumors or other lesions

• Blockages caused by kidney stones or an abdominal mass

• Abscesses

• Polycystic kidney disease

• Urinary incontinence or retention

• Kidney failure

• Defects you were born with

A CT scan is also useful when another type of exam, such as X-ray or physical exam, is not conclusive. CT scans of the kidney may be used to evaluate the back part of the belly. CT scans of the kidney may be used to help guide the needle placement in kidney biopsies.

After the removal of a kidney, CT scans may be used to locate abnormal masses in the empty space where the kidney once was. Your healthcare provider may have other reasons to recommend a CT scan of the belly.

What are the risks of a CT scan of the kidney?

You may want to ask your healthcare provider about the amount of radiation used during the test. Also ask about the risks as they apply to you.

Consider writing down all X-rays you get, including past scans and X-rays for other health reasons. Show this list to your provider. The risks of radiation exposure may be tied to the number of X-rays you have and the X-ray treatments you have over time.

Tell your provider if:

• You are pregnant or think you may be. Radiation exposure during pregnancy may lead to birth defects.

• You are breastfeeding. If contrast dye is used, talk with the radiologist about when to resume breastfeeding after contrast material is injected.

• You are allergic to or sensitive to medicines, contrast dyes, local anesthesia, iodine, or latex

• You have kidney failure or other kidney problems. In some cases, the contrast dye can cause kidney failure. People with kidney disease are more likely to have kidney damage after having contrast dye.

• Tell your healthcare provider if you are taking the diabetes medicine metformin. You may be told to stop taking this medicine before the scan.

You may have other risks that are unique to you. Be sure to discuss any concerns with your healthcare provider before the procedure.

Certain things can make a CT scan of the kidney less accurate. These include:

• Metal objects like surgical clips in your belly

• Barium in your intestines from a recent barium test

• Recent tests that used dye or other substances

How do I get ready for a CT scan of the kidney?

• Your healthcare provider will explain the scan to you and give you a chance to ask any questions.

• If your CT scan involves the use of contrast dye, you will be asked to sign a consent form that gives permission to do the procedure. Read the form carefully and ask questions if something is not clear.

• Tell the technologist if you have ever had a reaction to any contrast dye or if you are allergic to iodine. 

• Generally, you don't need to stop eating or drinking before a CT scan, unless a contrast dye will be used. Your healthcare provider will give you special instructions ahead of time if you need to fast.

• Tell the technologist if you are pregnant or think you may be.

• Tell the technologist if you have any body piercing on your chest or belly.

• Follow any other instructions your provider gives you to get ready.

What happens during a CT scan of the kidney?

You may have a CT scan as an outpatient or as part of your stay in a hospital. 

The way the test is done may vary depending on your condition and your healthcare provider's practices.

Generally, a CT scan of the kidney follows this process:

1. You will be asked to remove any clothing, jewelry, or other objects that may get in the way of the scan.

2. If you are asked to remove clothing, you will be given a gown to wear.

3. If you are having a procedure done with contrast, an IV line will be started in the hand or arm for injection of the contrast dye. For oral contrast, you will be given a liquid contrast to drink.

4. You will lie on a scan table that slides into a large, circular opening of the scanning machine. Pillows and straps may be used to prevent movement during the scan.

5. The technologist will be in another room where the scanner controls are located. But you will be able to see the technologist through a window at all times. Speakers inside the scanner will allow the technologist to talk to you and hear you. You will have a call button so that you can let the technologist know if you have any problems during the scan. The technologist will be watching you at all times and will be in constant communication.

6. As the scanner starts to rotate around you, X-rays will pass through your body for short amounts of time. You will hear clicking sounds and whirring sounds, which are normal.

7. The X-rays absorbed by the body's tissues will be detected by the scanner and sent to the computer. The computer will transform the information into an image to be interpreted by the radiologist.

8. It will be important that you stay very still during the scan. You may be asked to hold your breath at various times during the scan.

9. If contrast dye is used, you will be removed from the scanner after the first set of scans has been completed. A second set of scans will be taken after the contrast dye has been given.

10. If contrast dye is used for your procedure, you may feel some effects when the dye is injected into the IV line. These effects include a warm flushing sensation, a salty or metallic taste in the mouth, a brief headache, or nausea. These effects usually last for a few moments. Tell the technologist if you feel pain or tingling when the contrast is injected.

11. You should tell the technologist if you feel any breathing difficulties, sweating, numbness, or heart palpitations.

12. When the procedure is done, you will be removed from the scanner.

13. If an IV line was inserted, it will be removed.

14. You may be asked to wait for a short period of time while the radiologist examines the scans to make sure the images are clear.

The CT scan is not painful. You may have some discomfort or pain from lying still during the test. This may be because of recent surgery or injury. The technologist will use all possible comfort measures and do the scan as quickly as possible to reduce any discomfort or pain.

What happens after a CT scan of the kidney?

If contrast dye was used during your procedure, you may be watched afterward for any side effects or reactions to the contrast dye. These include itching, swelling, rash, or trouble breathing.

Tell your healthcare provider if you notice any pain, redness, or swelling at the IV site after you go home. This could be a sign of infection or other type of reaction.

Otherwise, you don't need any special care after a CT scan of the kidney. You may go back to your usual diet and activities unless your healthcare provider tells you otherwise.

Your healthcare provider may give you other instructions, depending on your situation.

Next steps

Before you agree to the test or procedure make sure you know:

• The name of the test or procedure

• The reason you are having the test or procedure

• What results to expect and what they mean

• The risks and benefits of the test or procedure

• What the possible side effects or complications are

• When and where you are to have the test or procedure

• Who will do the test or procedure and what that person’s qualifications are

• What would happen if you did not have the test or procedure

• Any alternative tests or procedures to think about

• When and how you will get the results

• Who to call after the test or procedure if you have questions or problems

• How much you will have to pay for the test or procedure