Medically reviewed by Prof. Dr. Aamer Nadeem Chaudhary, M.B.B.S., D.M.R.D., F.C.P.S. (Diagnostic Radiology), Consultant, Al-Nasar Lab & Diagnostic Centre. Updated September 2026.
Quick answer: KUB stands for Kidneys, Ureters and Bladder. It is a single plain X-ray of the abdomen used to look for kidney stones, bowel obstruction and perforation. It is fast and inexpensive, but it misses a significant share of kidney stones, including uric acid stones, which is why CT KUB has largely replaced it for stone diagnosis.
Book an abdominal X-ray: call 0300 0341944. Available at our collection centres and at our Johar Town campus.
What does a KUB X-ray show?
| Finding | How well X-ray shows it |
|---|---|
| Calcium containing kidney stones | Often visible, since they are dense |
| Uric acid stones | Invisible. They do not absorb X-rays enough to appear |
| Bowel obstruction | Good. Dilated loops and fluid levels are characteristic |
| Perforation | Free air under the diaphragm is a classic and important sign |
| Severe constipation and faecal loading | Yes, and it is a common finding in children |
| Swallowed foreign objects | Metal objects such as coins show clearly |
| Follow up of a known stone | Useful, if the stone was visible on the first film |
| Appendicitis | No. Ultrasound or CT is needed |
| Gallstones | Mostly no. Around four out of five are invisible. Ultrasound is the test |
| Organ disease, tumours, soft tissue | No. Needs ultrasound or CT |
Why does a KUB miss so many kidney stones?
This is the most important limitation to understand, because patients are often falsely reassured by a normal film.
Three things work against the X-ray. First, uric acid stones are radiolucent, meaning they let the beam pass through and leave no shadow at all. They simply do not appear. Second, small stones may be hidden behind bowel gas, stool or the bony pelvis. Third, a stone lying over the sacrum is frequently obscured.
The practical consequence: a normal KUB does not rule out a kidney stone. If someone has classic renal colic and the X-ray is clear, the next step is CT, not reassurance. A CT KUB detects essentially every stone regardless of composition, including the uric acid stones an X-ray cannot see.
There is a related point on our uric acid page: people who form uric acid stones are precisely the group whose stones are invisible on plain film.
So when is a KUB still worth doing?
It has not become useless. It remains sensible when:
- Following a known, previously visible stone to see whether it has moved or passed. Repeating a low dose X-ray is preferable to repeating CT scans
- Suspected bowel obstruction, where an erect and supine film gives a fast answer
- Suspected perforation, where free air under the diaphragm is decisive
- Checking the position of a ureteric stent or nasogastric tube
- Assessing severe constipation, particularly in children
- A swallowed foreign body
- When the patient cannot be moved easily and a portable film is the practical option
Which test for which symptom?
- Severe one sided loin pain radiating to the groin: CT KUB is the definitive test. A plain KUB may be done first in some settings, but a normal result should not end the investigation
- Right upper abdominal pain after fatty food: ultrasound, because gallstones are usually invisible on X-ray
- Right lower abdominal pain with fever: ultrasound first, then CT if unclear. Appendicitis is not an X-ray diagnosis
- Vomiting with a distended abdomen and no bowel movement: abdominal X-ray is a reasonable first test for obstruction
- Sudden severe generalised abdominal pain with a rigid abdomen: emergency assessment. An erect film looking for free air is part of it
- Ongoing unexplained abdominal pain: CT abdomen and pelvis answers far more
How to prepare
- Usually no preparation is needed, and in an emergency none is required
- For a planned KUB looking for stones, you may be asked to come with an empty bowel, since stool and gas obscure small stones. Follow whatever instruction you are given
- No fasting is needed unless the doctor has asked for it alongside another test
- Remove belts, buttons, zips, jewellery and anything from your pockets
- Tell the radiographer if you are or might be pregnant. An abdominal X-ray irradiates the pelvis directly, so it is usually deferred and ultrasound used instead. See X-ray safety in pregnancy
- You may be asked for both a lying and a standing film, since fluid levels and free air only show on the erect view
The images take a few minutes and you will be asked to hold your breath briefly.
Abdominal X-ray at Al-Nasar Lab
Al-Nasar Lab & Diagnostic Centre has served Lahore since 1996 and holds ISO 15189:2022 accreditation from the Pakistan National Accreditation Council. Plain abdominal and KUB X-rays are available with digital reporting by consultant radiologists, usually on the same day.
Where the X-ray cannot answer the question, ultrasound, CT KUB and CT abdomen are available at our Johar Town campus, so the next step does not mean starting again somewhere else. For patients who cannot travel, portable X-ray at home covers Lahore.
See our X-ray service page, the CT scan range, or contact us to book.
Frequently Asked Questions
Can a KUB X-ray detect all kidney stones?
No. Uric acid stones are invisible on X-ray, and small stones can be hidden by bowel gas or the pelvic bones. A normal KUB does not rule out a stone, and CT KUB is the definitive test.
Do I need to fast for an abdominal X-ray?
No fasting is required. For a planned stone search you may be asked to prepare the bowel so small stones are not obscured.
Can an abdominal X-ray show appendicitis?
No. Appendicitis is diagnosed with ultrasound or CT, supported by clinical assessment and blood tests.
Why do I need both a lying and a standing X-ray?
Because fluid levels in obstructed bowel and free air from a perforation only become visible on the erect film. The two views answer different questions.
Is an abdominal X-ray safe?
The dose is low and justified when the question matters. It is avoided in pregnancy because the beam passes directly through the pelvis, so always tell the radiographer if you are or might be pregnant.
This article is for general information and is not a substitute for medical advice. Please discuss your results with a qualified doctor.
