What is renal computerised tomography (CT)? 

Computerised tomography uses multiple X-rays and a computer to create detailed images of the inside of your body, including organs. It is a special type of X-ray using a scanner and a computer. It is different from standard X-rays as it produces pictures of cross-sections of the body.

A renal CT scan looks closely at the kidneys and surrounding areas. A liquid called contrast dye may be used to highlight the areas more clearly.

What does a renal CT scan involve?

You lie on a bed inside the CT scanner, a large, round machine with a tunnel. Some people say that it looks like a very large doughnut.

The bed moves slowly back and forward in the tunnel while the scanner beams X-rays into your body at different angles, to build up a detailed picture.

You need to lie still during the procedure.

Who is it for?

Your kidney doctor may request a renal CT scan to get more information for a diagnosis. You may have already had other tests, but they may not have given enough detail.

Is a renal CT scan safe? Are there any alternatives?

CT scans are generally safe, but they expose you to a higher dose of radiation than other imaging tests. We’re all exposed to low levels of radiation every day in the home and workplace – it comes from sources including building materials and some foods.

When you have a CT scan, you receive the amount of radiation you’d be exposed to naturally in around 9 months to 3 years.

It’s possible that exposure to higher levels may be linked to a raised risk of cancer later in life. However, the benefits of having a CT scan to help diagnosis are usually much greater than any potential risk.

If your kidney function is low, having contrast dye injected may reduce it further. Your hospital team will manage this risk. Reactions to the dye are unusual but tell your team if you’ve previously had an allergic reaction to iodine or contrast dye.

X-rays can be harmful to an unborn baby. Tell your hospital team if you are pregnant or think you might be.

Where will it take place?

CT scans are usually carried out in the hospital X-ray department.

Who will perform the CT scan?

A radiographer, a healthcare professional specialising in imaging tests, performs the scan.

What happens before the scan? How do I prepare?

• Follow any instructions you’re given.
• You can usually take your medication as usual but if you’re having contrast dye, you may be asked to stop eating and drinking for a short time beforehand.
• If you have diabetes and taking metformin, you should let the team doing the scan know. They might ask you to temporarily stop your metformin and might ask you to arrange a blood test with your GP within 1-2 weeks after your scan.
• Wear comfortable clothing and be aware you may need to remove anything with metal, such as zips and jewellery, which may interfere with the images.
• You’ll be asked about your medical history, including any allergies, and whether there’s a chance you could be pregnant.
• Tell your team if you feel anxious about being inside the CT scanner or have a fear of small spaces (claustrophobia). They can suggest ways to help you stay calm and may give you medicine to help you relax.

What happens during the CT scan? 

• The scan usually takes around 10-20 minutes and you’ll be in the unit for about 90 minutes in total.
• The radiographer will tell you whether you need to remove anything that might affect the scan.
• If contrast dye is being given through a vein, a small plastic tube called a cannula will be inserted into your hand or arm.
• The radiographer will position you on the machine’s bed, before leaving the room. They’ll operate the scanner from a control room next door, and will be able to see you through a window and speak to you via intercom.
• The bed slides slowly backwards and forwards through the scanner while the X-ray unit rotates around you, taking pictures. You may be asked to hold your breath at times.
• If contrast dye is injected, the radiographer will tell you when they’re doing it. You may feel a brief warm flush or the feeling that you have passed urine. You may also notice a metallic taste in your mouth.
• You need to stay very still during a CT scan. If you become uncomfortable, tell the radiographer that you need to move.

What happens immediately after the scan?

You’ll be able to go home and get back to your usual activities.

If contrast dye was injected, you may be asked to stay on the unit briefly for assessment, and you’ll be asked to drink extra fluids. The cannula will be removed before you leave.

What should I expect when I get home?

Make sure you follow any guidance you’re given by the hospital team.

If you had a cannula, a small bruise may develop where it was inserted.

How will I get the results?

A radiologist analyses the images and sends a report to your referring team, usually within two weeks. Your doctor will discuss the results and next steps with you.

Is there anything else I need to know?

Be prepared for a loud whirring noise inside the scanner as it takes pictures.

Publication date: 01/2026

Review date: 01/2029