Diagnostic Test
X-ray (KUB)
A quick, traditional X-ray used to spot kidney stones and check the position of stents.
Key Takeaways
- A quick, traditional X-ray used to spot kidney stones and check the position of stents.
- We offer specialist interpretation and related treatments. Book a consultation to discuss your options.
Overview
About X-ray (KUB)
A urological X-ray is a straightforward imaging test. The most common version is called a KUB, which stands for Kidneys, Ureters (the tubes), and Bladder. It works just like a standard X-ray of a bone, using a small amount of radiation to create a picture of the denser structures inside your tummy.
Test Information
Understanding Your Test
A detailed guide to your diagnostic procedure — from essential preparation and the purpose of the test to safety considerations and what to expect during the process.
The test is quick and simple. You will usually be asked to lie flat on a hard X-ray table, though sometimes you may need to stand against a vertical plate. A radiographer will position a large camera over your abdomen.
You must stay perfectly still and may be asked to hold your breath for a few seconds so the image doesn't blur.
A standard KUB X-ray is completely painless and takes less than a second to capture. The table can feel a bit hard and the room is often kept cool, but the process is very fast.
An KUB X-ray is may be done to see "radiopaque" stones—these are kidney or bladder stones made of calcium that are more likely to show up clearly on a plain X-ray. However, CT scanning is much more accurate, and so KUB X-ray is not used as often nowadays. It is also the standard way for doctors to check that a stent (a small tube inserted to help urine flow) is still in the correct position.
At a glance
Preparation required
- Metal Removal: You will need to remove jewellery, piercings, and any clothing with metal zips, underwires, or buttons, as these will show up on the X-ray.
- Pregnancy Check: It is vital to tell the radiographer if there is any chance you could be pregnant, as X-rays are generally avoided during pregnancy.
- Empty Bladder: You may be asked to pee just before the test starts.
Risks or considerations
- Radiation: You are exposed to a very small amount of radiation, similar to what you would naturally receive from the environment over a few months.
- "Invisible" Stones: Not all stones show up on X-rays. If your stones are made of uric acid (radiolucent), they may be invisible on this test and will require a CT scan instead.
- Movement: If you move during the "snapshot," the image will be blurry, and the radiographer may need to retake it.
What it can help diagnose
- Calcium-based Stones: Identifying stones in the kidneys, ureters, or bladder.
- Stent Monitoring: Ensuring a ureteric stent or catheter hasn't moved.
Our Commitment
Care you can trust
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Patient Guidance
Frequently Asked Questions
Common questions about this test and what to expect
3 questions
Not necessarily. About 80% of kidney stones are made of calcium and will show up as white spots on an X-ray (radiopaque). However, some stones, such as those made of uric acid, are 'radiolucent'—meaning they are invisible on a standard X-ray. If your symptoms suggest a stone but the X-ray is clear, a CT scan is usually the next step.
Reviewed 2 Mar 2026
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The radiation dose for a single KUB X-ray is very low—roughly equivalent to what you would naturally receive from the environment (background radiation) over about 3 to 6 months. While urologists aim to keep radiation 'As Low As Reasonably Achievable' (ALARA), the diagnostic benefit usually far outweighs the minimal risk.
Reviewed 2 Mar 2026
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A CT scan provides a 3D view and can see stones of all compositions, as well as providing much better detail of the soft tissues like the kidneys and bladder. While X-ray is faster and cheaper, CT is the 'gold standard' for most urological emergencies because it is much more accurate and less likely to miss a diagnosis.
Reviewed 2 Mar 2026
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