About a CT KUB scan
KUB stands for kidneys, ureters and bladder, the parts of the urinary system. The kidneys filter the blood to make urine, which passes down two thin tubes (the ureters) to the bladder. A CT KUB is a quick CT (computed tomography) scan of these organs, usually done with a low-dose technique and without contrast dye.
The main use of a CT KUB is to look for kidney stones. Almost all stones show up clearly on CT, and the scan shows how big they are, exactly where they are, and whether a stone is blocking the flow of urine and causing the kidney to swell (hydronephrosis). This helps doctors decide whether a stone is likely to pass on its own or needs treatment. NICE recommends low-dose non-contrast CT as the first scan for adults with suspected renal colic, the severe pain caused by a stone moving down the ureter. It is also used to check on stones over time and before and after treatment.
Because no contrast is used, a CT KUB is not designed to look for growths or the cause of blood in the urine; a CT urogram is used for that. In pregnancy, an ultrasound is used instead of CT. For a wider look at the tummy, see CT abdomen and pelvis.
What happens during the scan
You lie on your back, or sometimes on your front, on the scanner bed with your arms raised above your head. The bed moves through a short, open ring while your tummy and pelvis are scanned. The radiographer controls the scanner from the next room, but can see, hear and talk to you throughout. You will be asked to hold your breath for a few seconds. The scan itself takes less than a minute, and no injection is needed.
Is CT safe?
CT uses X-rays, which are a type of ionising radiation. A CT KUB uses a low-dose technique, so the dose is much lower than for a standard CT of the abdomen and pelvis (about 10 mSv). People who form stones often need repeat scans, and the low-dose technique helps keep the total dose down. The risk from a single scan is very small, and every CT scan is checked by a radiologist or radiographer to make sure the benefit of the scan outweighs the risk, as required by the Ionising Radiation (Medical Exposure) Regulations. If you have had other CT scans recently, tell us when you book.
What the scan can show
A CT KUB can help to look at:
- kidney and ureteric stones, including their size and position
- blockage of the kidney or ureter (hydronephrosis)
- bladder stones
- stones before and after treatment
- some other causes of pain in the side (loin) or groin
When to get urgent help: go to A&E or call 999 if you have severe pain in your side, back or groin with a high temperature or shivering, if you have only one kidney and develop this pain, if you cannot pass urine, or if the pain is so severe that painkillers do not help. An infected or blocked kidney needs emergency treatment. Do not wait for a private scan.
Preparing for your scan
No special preparation is usually needed, and you can eat and drink normally. Some centres ask you to drink some water beforehand so your bladder is comfortably full. Upload any previous scan reports and letters from your urologist when you book.
Wear loose, comfortable clothing without metal zips, poppers or buttons, and leave jewellery at home, as metal in the scan area can affect the pictures. You may be asked to change into a gown. Unlike MRI, CT is not affected by pacemakers or most metal implants, and the scanner is a short open ring rather than a tunnel, so it is usually easier for people who feel anxious in enclosed spaces.
Tell the team before your scan if you are, or might be, pregnant or breastfeeding, if you have kidney problems, diabetes (especially if you take metformin), asthma, thyroid problems or allergies, or if you have had a reaction to contrast dye before. If you need contrast, you may be asked for a recent kidney blood test result.
Frequently asked questions
Does a CT KUB need contrast?
No. A CT KUB is done without contrast, as stones show up clearly on their own. There is no injection.
Can a CT KUB find the cause of blood in my urine?
It can show stones, but it is not designed to look for growths in the kidneys or the lining of the urinary tract. If you have blood in your urine, a CT urogram and other tests are usually needed. See a GP if you notice blood in your urine.
Is CT KUB better than ultrasound for kidney stones?
CT KUB is more accurate at finding stones, especially small stones and stones in the ureter. Ultrasound avoids radiation and is used in pregnancy and for children.
Do I need a referral?
Because CT uses radiation, each scan has to be justified by a qualified professional before it can go ahead. Upload a referral from your GP or consultant when you book if you have one. If you do not, select “no referral” and the scanning centre will review your request and confirm the next steps with you, which may include arranging a referral.
Sources
- NICE NG118 – Renal and ureteric stones: assessment and management
- NHS – Kidney stones: diagnosis
- NHS – Kidney stones
- RadiologyInfo.org – CT of the Abdomen and Pelvis
- NHS – CT scan
- UKHSA – Patient dose information: guidance
The information on this page has been gathered from various sources and is provided for general information only. It is not medical advice. TOP MRI is not liable for the accuracy or completeness of this information. Please speak to your doctor or the scanning centre about your own situation.