Kidney ultrasound (Renal (kidney) ultrasound scan)
A usually not painful scan that uses sound waves to look at the size, shape and structure of your kidneys, and often your bladder, without any radiation.
✓ Medically reviewed by a GMC-registered consultant · last reviewed September 2026 · next review September 2027 · how we review
In short
- A kidney ultrasound is a usually not painful, radiation-free scan that looks at the structure of the kidneys and often the bladder.
- It is good at finding blockages, swelling, stones, cysts and changes in kidney size, but it cannot measure kidney function or always see small stones or early tumours.
- It is quick (about 10–30 minutes), needs little preparation beyond sometimes a full bladder, and has no recovery time.
- Ask what question the scan is meant to answer, and what happens if it is normal, abnormal or shows something incidental.
A plain-English summary. The detail — including risks and recovery — is below.
At a glance
A general guide. Your radiologist will give you advice for your situation.
Shows the size, shape and structure of the kidneys without radiation or needles
Using ultrasound to measure kidney function — blood tests, not imaging, do that.
Usually not painful, about 10–30 minutes. You may need a full bladder at the start and be asked to hold breaths or change position.
A clear route to receive the written report and a clinician to explain it.
Usually not painful, about 10–30 minutes. You may need a full bladder at the start and be asked to hold breaths or...
The gel is wiped off and you can eat, drive and return to work or normal activities immediately.
A written report is sent to the doctor who requested the scan, who explains what it means for you.
You may be offered a further test (such as a CT or MRI scan, or a biopsy) or a specialist referral, depending on...
What is a kidney ultrasound?
A kidney (renal) ultrasound is a scan that uses high-frequency sound waves to create live pictures of your kidneys, and often your bladder and the tubes that drain them. A small hand-held probe (a transducer) is moved over your skin, and the echoes are turned into images on a screen. It uses no radiation and no needles, and is generally usually not painful.
It is often requested when blood or urine tests suggest a kidney problem, or for symptoms such as blood in the urine, repeated urine infections, or pain in the side. It can show the size and shape of the kidneys, whether they look scarred or swollen, whether the drainage is blocked (causing the kidney to swell), and whether there are stones, cysts or other lumps.
An ultrasound is very good at answering structural questions, but it has limits. It cannot measure how well the kidneys are working (that is what blood tests do), it does not always see small stones or early tumours, and it cannot tell what a lump is made of. It is often a first step, with other tests added if needed.
This guide explains what the scan involves and what it can and cannot show. It is not a diagnosis.
Types, options & approaches
There may be different ways to do this. The right approach depends on the clinical question and your circumstances.
Ultrasound versus CT for the kidneys
| Feature | Ultrasound | CT scan |
|---|---|---|
| Radiation | None | Uses X-rays (radiation) |
| Good for | Blockage, swelling, cysts, kidney size | Stones, detailed anatomy, staging tumours |
| Small stones / early tumours | May be missed | More sensitive |
| Contrast dye | Not usually needed | Often used; affects some kidney patients |
The two tests answer different questions and are often complementary. Your doctor chooses based on what needs to be looked at.
Preparing for your scan
- Ask whether you need a full bladder; for a kidney-and-bladder scan you are often asked to drink water beforehand and not empty your bladder until told.
- If a full bladder is needed, you may be asked to finish about a litre of water around an hour before and hold on until the scan.
- Wear loose, comfortable clothing, as you will need to expose your tummy and back.
- You can usually eat and take your medicines as normal unless told otherwise.
- Mention if you might be pregnant; ultrasound is safe in pregnancy, but it helps the team plan.
- Bring details of any previous scans or relevant test results.
- Allow time, as you may be asked to wait if your bladder is not yet full enough.
What happens
You usually lie on a couch and expose your tummy and lower back. The person doing the scan (a sonographer or radiologist) puts a little warm gel on your skin to help the sound waves travel, then moves a hand-held probe over the area. You may be asked to take a breath and hold it briefly, or to roll onto your side, so the kidneys can be seen clearly behind the ribs.
If your bladder is being checked, it is usually scanned first while full, and you may then be asked to empty it and have a quick repeat scan to see how well it drains. The scan is usually not painful, though the probe may press a little. It usually takes about 10 to 30 minutes.
Afterwards the gel is wiped off and you can get dressed and go straight home or back to work. The images are reviewed and a written report is sent to the doctor who requested the scan.
Is this scan right for me?
A good consultation should explore whether it's the right choice for you now — including reasons to wait or consider something else.
May not be suitable if…
- Using ultrasound to measure kidney function — blood tests, not imaging, do that.
- Relying on ultrasound alone to rule out kidney stones, where a CT scan is more sensitive.
- Expecting ultrasound to characterise every lump; some need CT, MRI or biopsy.
- Using it as the sole test when symptoms strongly suggest a problem it may miss.
Delay or rearrange if…
- You cannot tolerate a full bladder when one is needed, until this can be managed.
- There is an urgent problem needing immediate care (such as a blocked, infected kidney), where treatment should not wait for a routine scan.
- Recent abdominal surgery or wounds make scanning the area difficult, until advised.
- Preparation instructions (such as drinking water) have not been followed, which may mean rebooking.
Alternatives to discuss
- CT scan for detailed views, stones or staging a tumour (uses radiation).
- MRI scan for soft-tissue detail without radiation in selected cases.
- Kidney function blood tests and urine tests to assess how the kidneys are working.
- A kidney biopsy where tissue is needed to find the cause of a problem.
Before you decide
Use this as a shared-decision checklist. The aim is not just “can this be done?”, but whether it is right for you, now, with the risks and alternatives clearly understood.
What matters most to me?
Think about symptoms, daily life, work, caring responsibilities, sport, fertility, travel, appearance and anxiety — the right choice depends on your priorities, not just the medical facts.
What are all my options?
Ask about waiting, monitoring, medicines, rehabilitation, a smaller or larger procedure, a different test, NHS referral, or a second opinion where that would help.
What would make me pause?
Active infection, pregnancy, unstable medical problems, smoking, medicines that increase bleeding, poor support at home, or feeling pressured are all reasons to slow down and get tailored advice.
What happens if I do nothing today?
For some problems, waiting is safe; for others, delay can make treatment harder. A good consultation should explain the trade-off in plain English.
Benefits
- Shows the size, shape and structure of the kidneys without radiation or needles
- Can detect a blockage that is making a kidney swell, which may need prompt treatment
- Can find stones, cysts and many lumps, and check kidney size in long-term kidney disease
- Safe to repeat and suitable in pregnancy and for children
- Quick, usually not painful and needs no recovery time
- Helps decide whether further tests, such as a CT scan or biopsy, are needed
Risks & complications
- Mild discomfort from a full bladder while waiting and during the scan
- Pressure from the probe, especially over a tender area
- Inconvenience of preparation and possible waiting
- A normal scan that does not fully explain your symptoms, so more tests are needed
- Incidental findings, such as a harmless cyst, that lead to further tests or worry
- A finding that is unclear and needs another scan (such as CT or MRI) to clarify
- Limited views in some people (for example where bowel gas or body shape gets in the way)
- A small stone or early tumour being missed because ultrasound cannot see everything
- False reassurance from a normal scan when the problem needs a different test
An ultrasound has no radiation and no physical risk, so the main issues are its limits, not harm. It cannot measure kidney function, can miss small stones or early tumours, and cannot always say what a lump is. It is often a first look, and a normal scan does not rule out every problem. Ask what the scan is meant to answer and what the plan is if it is normal, abnormal or shows an incidental finding.
Published figures to discuss
Ultrasound is safe and carries no radiation, so the meaningful 'rates' concern its accuracy rather than complications. Its sensitivity depends on what is being looked for, the patient's body and the operator: it is good for blockage and kidney size but can miss small stones and early tumours. Because this varies so much by question and setting, single reliable percentages are not meaningful here, and the limitations are best described in words.
| Figure | Reported range | How to interpret it | Source / confidence |
|---|---|---|---|
| Physical harm from ultrasound | Very low | Diagnostic ultrasound does not use ionising radiation and is non-invasive. | Guide sourcesClinical context |
| Small stones or early disease missed | Recognised limitation | Ultrasound is good for obstruction and kidney size, but CT or other tests may be needed for some stones or masses. | Guide sourcesClinical context |
| Incidental cysts or findings cause anxiety | Common | Simple kidney cysts are common and usually harmless, but complex findings need follow-up. | Guide sourcesClinical context |
| Result interpreted without urine/blood tests | Avoidable | Kidney imaging should be linked to eGFR, ACR, urinalysis, blood pressure and symptoms. | Guide sourcesClinical context |
These are literature figures, not a personalised prediction. Your own risks and likely benefits depend on your circumstances, your health, and how your care is carried out and followed up.
What happens afterwards
There is no physical recovery from an ultrasound. You can return to normal activities immediately. What matters afterwards is getting the report and understanding what it means for your care.
- Needing to empty a full bladder with relief once the scan is done
- No after-effects, so normal activity straight away
- A short wait of a few days for the written report
- Sometimes being asked back for a further or repeat scan
- Being reassured if the scan is normal, while other tests continue if needed
Aftercare
- Make sure you know how and when you will get the result, and who will explain it.
- Ask what the scan was looking for and whether it answered the question.
- If an incidental finding is reported, ask what it means and whether it needs anything done.
- Keep any follow-up scan or specialist appointment that is arranged.
- Remember the scan does not measure kidney function, so blood and urine tests may still be needed.
- Ask whether a normal scan rules out your symptoms or whether another test is needed.
- Keep a copy of the report and any images for your records if you can.
- Clarity on whether you need a full bladder, and how much to drink
- Loose, comfortable clothing for the appointment
- Details of any previous scans or relevant results
- A note of what the scan is meant to answer
- Agreed way to receive the report and who will explain it
- A plan for what happens if the scan is normal, abnormal or shows an incidental finding
- Any follow-up test or appointment diarised
⚠ Get urgent help if…
- Severe pain in the side or back, especially with fever (possible blockage or infection)
- Being unable to pass urine, or passing much less than usual
- Visible blood in the urine
- High fever, shivering or feeling very unwell
- Worsening symptoms while waiting for the result
- These warning signs relate to the underlying kidney problem rather than the scan itself, which has no after-effects
Who to contact: your clinician, clinic or test provider first (keep their number to hand). For urgent advice when you can't reach them, call NHS 111. In an emergency, call 999.
General guidance — it doesn't replace the specific advice your radiologist gives you.
Results & realistic expectations
A normal scan means the kidneys look a normal size and shape, there is no obvious blockage, and no clear stones, cysts or lumps were seen. That is reassuring, but it does not rule out everything, because ultrasound can miss small stones and early tumours and cannot measure kidney function. An abnormal scan might show a blocked, swollen kidney, scarring, a stone, a cyst or a lump, each of which is followed up differently.
The report goes to the doctor who requested the scan, usually within a few days, and is read alongside your symptoms and blood and urine tests. Often the scan is one piece of the picture, and a clear answer comes from putting the results together rather than from the scan alone.
An ultrasound is a snapshot of how things look on the day. Findings can change, so a scan may be repeated to watch a cyst, monitor a blocked or shrinking kidney, or check progress over time. A normal scan now does not guarantee things will stay the same, and new symptoms may warrant a fresh look. Your doctor will advise whether and when a repeat scan is needed.
Related tests, treatments or support
A kidney ultrasound is usually interpreted alongside kidney function blood tests and urine tests, because the scan shows structure while the blood tests show function. If the scan raises questions, a CT or MRI scan may give more detail, and a kidney biopsy may be used to find the cause of a problem the scan cannot explain.
Follow-up & long-term care
Follow-up depends on what the scan shows. A normal scan with ongoing symptoms may lead to other tests; an abnormal scan may lead to a CT or MRI, a specialist referral, or treatment of a blockage or infection. Make sure you know who will explain the report, when, and what the plan is for any finding.
- Repeat ultrasound to monitor a cyst, a blocked kidney or kidney size over time
- Regular scans for some long-term kidney conditions, as advised
- Surveillance of a transplanted kidney where recommended
- Combining future scans with blood and urine tests to track both structure and function
Repeat, follow-on and what comes next
- A scan may be repeated to monitor a cyst, a blockage or kidney size over time.
- An unclear finding often needs a further test (CT, MRI or biopsy) to clarify it.
- Views can be limited in some people, occasionally needing a repeat or different scan.
- Ultrasound is frequently a first step, with other tests added to complete the picture.
Ask what happens if the result is unclear or needs repeating, and what is included if further tests or follow-up are needed.
What good aftercare looks like
- A clear route to receive the written report and a clinician to explain it.
- An explicit plan for normal, abnormal and incidental findings.
- Combining the scan with blood and urine tests to assess both structure and function.
- Timely onward referral or further imaging when a finding needs it.
- Sensible advice on when a repeat scan would be useful.
What affects the cost
Costs vary a great deal between people and providers, and we don't publish prices. What matters is understanding what drives the cost and making sure your quote is complete. The main things that affect it:
- Whether the scan is of the kidneys alone or kidneys and bladder
- Whether a Doppler (blood-flow) study is included
- Who performs and reports the scan, and how quickly the report is turned around
- Whether a consultation to explain the result is included
- Whether follow-up or repeat scans are part of the package
- Any further imaging (CT or MRI) needed to clarify a finding
- Exactly what the scan covers (kidneys only, or kidneys and bladder)
- Who reports the scan and how quickly you receive the written report
- Whether a clinician explains the result to you
- What happens, and what it costs, if a further scan is needed to clarify a finding
- Whether follow-up or repeat scans are included
- How incidental findings would be handled
- What happens if you need referral into NHS care
On the NHS? Kidney ultrasound is routinely available on the NHS when clinically indicated and is also widely available privately; people sometimes go private for speed, but the scan and its limits are the same.
You're entitled to your total cost in writing — including reports, follow-up and what happens if the result is inconclusive — before you decide.
Consent traps and marketing red flags
These are not small details. They are often where patients lose choice, time to reflect, or realistic expectations.
Consent traps
- Believing a normal ultrasound rules out all kidney disease, including stones and early tumours.
- Thinking the scan measures kidney function when it shows structure only.
- No plan for what an incidental finding means or whether it needs action.
- No clear route for receiving and understanding the report.
- Not being told another test may be needed if the scan is inconclusive.
Marketing red flags
- Promoting a kidney ultrasound as a complete 'kidney health check' on its own.
- Implying a normal scan guarantees healthy kidneys or rules out cancer.
- Not mentioning that ultrasound can miss small stones and early tumours.
- Bundling unnecessary scans without a clear clinical question.
- Offering supplements or 'detox' products alongside the scan.
Choosing a specialist safely
- Check the radiologist is on the GMC Specialist Register for this area.
- Make sure they work at a CQC-registered service, and look for membership of the relevant Royal College or professional body.
- You're entitled to time to consider and to have your questions answered before you agree — the radiologist who looks after you should explain it, not a salesperson.
- Be wary of pressure: time-limited offers or deposits taken before you've had time to think are red flags, not bargains.
- You're entitled to your total cost in writing — including any follow-up — before you decide.
Questions to ask your medical professional
Take this to your consultation. A good radiologist will welcome every one of these.
- What is this scan meant to look for in my case?
- Will it check my bladder as well, and do I need a full bladder?
- What happens if the scan is normal but my symptoms continue?
- If something is found, what would the next step be?
- Do I also need blood or urine tests, since the scan does not measure function?
- Who will explain the report to me, and when?
- If an incidental finding is reported, how will we decide whether it matters?
- Are you on the GMC Specialist Register for this area, and which Royal College or professional body are you a member of?
- Will you be the radiologist who carries out my scan, and who looks after me afterwards?
- What are the risks for someone like me, and how often do your own patients have a problem or need it repeated or redone?
- What does a realistic result look like — and what can this scan not achieve?
- What are my options, including waiting, doing nothing for now, or choosing a different approach?
- Can I have written information, results and aftercare instructions in a format I can use, including any accessibility or communication support I need?
- What is the total cost in writing, including any follow-ups, and how much time do I have to decide?
Frequently asked questions
Does a kidney ultrasound hurt?
Do I need a full bladder?
Will the scan tell me how well my kidneys are working?
Can an ultrasound miss things?
How soon will I get the result?
Is a kidney ultrasound available on the NHS?
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How we made this page
Medically reviewed by a GMC-registered consultant. Written in plain English, checked against NHS, NICE, GMC and relevant Royal College / specialist-society guidance, and kept under review. No clinic paid to appear on this page, and we publish no pricing. This is general information to help you prepare — it is not a substitute for advice from your own clinician. How we review our guides →
Source hierarchy: UK regulator and NHS/NICE guidance first, then relevant Royal College or specialist-society guidance, then peer-reviewed evidence for procedure-specific figures where available.
Sources & standards: Kidney Care UK — Renal (kidney) ultrasound Guy's and St Thomas' NHS FT — Kidney and bladder ultrasound scan NHS — Ultrasound scan Royal Berkshire NHS FT — Having a urinary/renal tract ultrasound UK Kidney Association — information resources
Reviews reflect patients' experience of care, not clinical outcomes. For procedure volumes and outcome data see PHIN.
Last medically reviewed 2026-09-21. Spotted something wrong or out of date? Report an error in this guide.
Related guides: Kidney function blood tests (eGFR) · Kidney biopsy · Investigating jaundice · Acute kidney injury treatment · Anaemia of kidney disease management