Suspected pulmonary embolism assessment
The tests and scoring a doctor uses to find out whether sudden breathlessness, chest pain or a swollen leg is caused by a blood clot on the lung.
✓ Medically reviewed by a GMC-registered consultant · last reviewed September 2026 · next review September 2027 · how we review
In short
- It works out whether sudden breathlessness, chest pain or a swollen leg is caused by a clot on the lung, using a clot score, a blood test and usually a scan.
- Sudden breathlessness, chest pain or collapse needs 999 or A&E straight away — do not wait for a private booking and do not drive yourself.
- A normal D-dimer in a low-risk person can rule a clot out; a raised D-dimer does not prove a clot and usually leads to a scan.
- Treatment (a blood-thinning injection) is often started before the scan result if a clot is thought likely, because the danger of an untreated clot is high.
A plain-English summary. The detail — including risks and recovery — is below.
At a glance
A general guide. Your specialist will give you advice for your situation.
Quickly confirms or rules out a clot on the lung, which is a potentially life-threatening condition
A private outpatient assessment is the wrong setting for anyone with sudden severe breathlessness, chest pain, collapse or low oxygen — these need 999/A&E...
Blood tests, oxygen and heart checks, a clot score, and usually a scan. A blood-thinning injection may be given before the result if a clot is thought...
A named contact and clear instructions on when to return urgently or call 999.
Blood tests, oxygen and heart checks, a clot score, and usually a scan. A blood-thinning injection may be given...
The scan is usually reported within hours. You are told whether a clot was found, started or continued on...
If a clot is confirmed, blood-thinning treatment is established, often as tablets. You are told what to watch for...
A follow-up is arranged to confirm the treatment plan, look for an underlying cause, and decide how long...
What is an assessment for suspected pulmonary embolism?
A pulmonary embolism (PE) is a blood clot that has travelled to the lungs, usually from a vein in the leg. It can be life-threatening, so the assessment is about answering one urgent question quickly and safely: is a clot the cause of your symptoms, and do you need treatment now?
The assessment is not a single test. A doctor takes your history, examines you, works out how likely a clot is using a structured score (commonly the Wells score), and then chooses tests. These usually include a blood test called a D-dimer and, in many people, a CT pulmonary angiogram (CTPA) — a special CT scan of the lung blood vessels using contrast dye. Some people have a different scan (a V/Q scan) instead.
The point of the pathway is to confirm or rule out a clot without scanning everyone unnecessarily. A blood-thinning injection is often started before the scan result is back if the doctor thinks a clot is likely, because the risk of waiting can outweigh the risk of treating.
This is genuinely emergency medicine. If you have sudden breathlessness, chest pain that is worse when you breathe in, you are coughing up blood, or you have collapsed, this is a 999 or A&E situation now — not something to arrange through a routine private appointment.
Types, options & approaches
There may be different ways to do this. The right approach depends on the clinical question and your circumstances.
Options at a glance
These are the main approaches described in this guide. The right option depends on the diagnosis, your goals and what your clinician thinks is safe.
Clinical probability score (Wells score)
A structured set of questions and findings that sorts people into 'PE likely' or 'PE unlikely'. It decides who needs a scan and who can be safely checked with a blood test...
D-dimer blood test
Measures a breakdown product of blood clots. A normal result in a low-probability person makes a clot very unlikely and can avoid a scan. It is often raised for many reasons...
CT pulmonary angiogram (CTPA)
A CT scan of the lung arteries with contrast dye injected into a vein. It is the usual scan to look directly for a clot. It involves radiation and contrast, so it is used...
Ventilation/perfusion (V/Q) scan
An alternative lung scan used when contrast dye is unsuitable (for example a serious contrast allergy or poor kidney function), in pregnancy in some cases, or when CTPA is...
Preparing for your test
- If symptoms are sudden or severe, do not prepare or wait — call 999 or go to A&E, and say you may have a clot on the lung.
- Bring a list of your medicines, especially any blood thinners, the contraceptive pill or HRT, and recent hormone treatment.
- Tell the team about recent surgery, long flights, immobility, cancer, pregnancy or a previous clot, as these raise the risk.
- Mention any contrast-dye allergy and any kidney problems, as these affect whether a CTPA or a V/Q scan is used.
- Tell the team if you are or might be pregnant, as this changes which scan and which scoring approach is safest.
- You do not usually need to fast for these tests, but follow whatever the assessing unit tells you on the day.
What happens
A doctor or acute physician asks about your symptoms and risk factors, examines you, and checks your oxygen levels, pulse, blood pressure and an ECG. They calculate your clot probability score.
If a clot is judged unlikely, you usually have a D-dimer blood test. If that is normal, a clot is very unlikely and you may avoid a scan. If the D-dimer is raised, or if a clot is judged likely from the start, you are offered a scan — most often a CTPA, sometimes a V/Q scan.
If the doctor thinks a clot is likely, they often start a blood-thinning injection before the scan result comes back, because treating early is usually safer than waiting. The scan is normally reported within a few hours. You may be kept in, sent to a same-day emergency care unit, or discharged with a clear plan, depending on what is found and how well you are.
Is this test 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…
- A private outpatient assessment is the wrong setting for anyone with sudden severe breathlessness, chest pain, collapse or low oxygen — these need 999/A&E and emergency-level monitoring.
- Routine D-dimer testing is the wrong test in someone already judged high-probability, who should go straight to imaging.
- CTPA may be unsuitable in serious contrast allergy or significant kidney impairment, where a V/Q scan is considered instead.
- The pathway is not a screening test for clots in people without symptoms or risk factors.
Delay or rearrange if…
- There is any sign of an emergency — do not delay assessment, escalate to 999/A&E immediately.
- Pregnancy is possible, until the team has chosen the safest scan and scoring approach.
- Kidney function or contrast allergy status is unknown and a contrast scan is being considered.
- Recent results or imaging that would change the plan are not yet available.
Alternatives to discuss
- A structured clot score plus a normal D-dimer to safely avoid imaging in lower-risk people.
- A V/Q scan instead of CTPA when contrast is unsuitable.
- Leg vein ultrasound when a DVT is the more likely problem.
- Looking for and treating an alternative cause (such as chest infection or anxiety) when a clot is excluded.
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
- Quickly confirms or rules out a clot on the lung, which is a potentially life-threatening condition
- Lets safe, effective blood-thinning treatment start early when a clot is likely
- A structured score plus a normal D-dimer can safely avoid an unnecessary scan in lower-risk people
- Can pick up other causes of your symptoms, such as pneumonia or fluid on the lung
- Gives you and your doctor a clear plan, including how long any treatment should continue
Risks & complications
- Bruising or discomfort where blood is taken or the drip is placed
- A raised D-dimer that does not mean a clot, leading to a scan you might not have needed
- Waiting and uncertainty while results come back
- A warm flushing feeling as contrast dye is injected for a CTPA
- Incidental findings on the CT scan (something unrelated that then needs further tests)
- A contrast reaction (itching, rash, rarely something more serious)
- A worsening of kidney function after contrast dye in people already at risk
- Finding a very small (subsegmental) clot whose treatment is genuinely uncertain
- A serious allergic reaction to contrast dye
- A missed clot if the scan is taken too early, technically limited, or the wrong test is chosen
- Bleeding from blood-thinning treatment started before the diagnosis is confirmed
The two biggest pitfalls are at opposite ends. Missing a clot can be fatal, so genuine emergency symptoms must go through 999/A&E. But over-testing has its own harms: a raised D-dimer is common and non-specific, CTPA involves radiation and contrast, and very small clots can be over-diagnosed and over-treated. Ask why a particular test is being done, what the result will change, and whether a clot score and D-dimer can safely avoid a scan in your case.
Published figures to discuss
Reliable single percentages are hard to quote because they depend heavily on how likely a clot was before testing, the population studied and the technology used. The figures below are illustrative ranges from published series and should be treated cautiously, not as your personal risk.
| Figure | Reported range | How to interpret it | Source / confidence |
|---|---|---|---|
| Worsening kidney function after contrast for CTPA | Reported up to around 12% in some series, with higher figures where pre-existing risk is high | Estimates vary widely with definition and patient mix; people with normal kidneys and good hydration are at much lower risk. | Diagnostic yield and renal complications after CTPA (PMC)pmc.ncbi.nlm.nih.govPublished figure |
| False-positive isolated subsegmental (very small) PE | Reported up to around 40% in some studies of small clots | This is why treatment of tiny clots is debated and decided case by case, not automatically. | Diagnostic yield and renal complications after CTPA (PMC)pmc.ncbi.nlm.nih.govPublished figure |
| Incidental findings on CTPA | Common; one series reported around 3 incidental findings per patient | Many are harmless but can trigger further tests and anxiety. | 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 the assessment itself. What matters afterwards is the result, any treatment that follows, and a clear plan for how long it continues and how you are monitored.
- Mild bruising where blood was taken or a drip was placed
- Tiredness and anxiety after an emergency assessment
- A short period of uncertainty while waiting for the scan report
- If treated, getting used to a blood thinner and the monitoring around it
Aftercare
- If a clot is confirmed, take blood-thinning medicine exactly as directed and do not stop it without advice.
- Learn the warning signs of bleeding (such as black stools, blood in urine, or a bad headache) and who to contact.
- Keep all follow-up appointments, as the plan for how long to treat is reviewed deliberately over time.
- Tell any other clinician, dentist or pharmacist that you are on a blood thinner before procedures or new medicines.
- Ask whether you need tests for an underlying cause, especially if the clot had no obvious trigger.
- Seek emergency help again for sudden breathlessness, chest pain or collapse — these can mean a further clot.
- Ask about safe activity, travel and, for women, whether hormone treatments need changing.
- Up-to-date list of all your medicines, including the pill or HRT
- Note of recent flights, surgery, immobility or previous clots
- Any record of a contrast-dye allergy or kidney problems
- Someone to be with you and help you get home safely
- A written copy of your result and treatment plan
- The unit's contact number for questions or worsening symptoms
- Clear instructions on warning signs that mean returning urgently
Scars and how they heal
There are no surgical wounds. You may have a small bruise or puncture mark where blood is taken or a drip (cannula) is placed in the back of the hand or arm. These settle within days.
⚠ Get urgent help if…
- Sudden breathlessness or breathlessness that is getting worse — call 999
- Chest pain, especially pain that is worse when you breathe in — call 999
- Coughing up blood — call 999
- Feeling faint, collapsing, or a racing or irregular heartbeat — call 999
- A painful, swollen, hot leg (possible DVT) — seek urgent medical advice
- If you are on a blood thinner: heavy or unusual bleeding, black stools, or a sudden severe headache — seek urgent help
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 specialist gives you.
Results & realistic expectations
A clear result either confirms a clot (so treatment continues) or makes one very unlikely (so the team looks for another cause of your symptoms). A normal D-dimer in a low-probability person is reassuring and can avoid a scan. A normal scan in someone who was higher risk is also reassuring but should come with an explanation of what else might be going on.
No single test is perfect. Scans can occasionally miss clots or find very small ones whose importance is uncertain, and a raised D-dimer has many causes. A good assessment treats the result alongside your story and risk factors, not in isolation.
The result tells you about this episode only. It does not stop a future clot. If you have a clot confirmed, the plan for how long to take blood thinners is reviewed over months, weighing the chance of another clot against bleeding risk. If you develop new symptoms later, you may need to be assessed again from scratch.
Related tests, treatments or support
The assessment is often combined with a leg vein ultrasound if a DVT is suspected, an ECG and chest X-ray to look at other causes, and blood tests for infection or strain on the heart. If a clot is found without an obvious cause, your team may discuss whether further investigations are appropriate.
Follow-up & long-term care
If a clot is confirmed, you should have clear follow-up to establish treatment, look for a cause and review the duration of anticoagulation, commonly around three months. If a clot is ruled out, you should still leave with an explanation for your symptoms and advice on when to seek help again.
- If on a blood thinner, attend any monitoring blood tests advised for your medicine
- Keep a current medicines list and share it before any procedure
- Discuss travel, immobility and hormone treatments that may raise future clot risk
- Know your personal warning signs and the plan if symptoms return
Repeat, follow-on and what comes next
- A normal scan does not always end the matter; if symptoms persist or worsen, re-assessment may be needed.
- A raised D-dimer commonly leads on to imaging that turns out normal.
- Very small clots may be found whose treatment is genuinely uncertain and needs a senior decision.
- If a clot is confirmed, the duration of treatment is itself reviewed and may be extended or stopped over time.
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 named contact and clear instructions on when to return urgently or call 999.
- A written copy of the result and, if treated, the anticoagulation plan and its planned review.
- A deliberate plan to look for an underlying cause when a clot has no obvious trigger.
- Clear safety-netting if a clot was excluded but symptoms continue.
- Joined-up handover to your GP and any specialist managing ongoing treatment.
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 a clot score and D-dimer can settle the question or a scan is needed
- The type of scan used (CTPA versus V/Q) and whether contrast is required
- The reporting radiologist and how quickly the report is needed
- Additional tests such as leg ultrasound, ECG or blood tests for an underlying cause
- Whether treatment, monitoring and follow-up are included in any package
- Whether admission or same-day emergency care is needed while results are awaited
- The assessing clinician's (acute physician's) fee
- Blood tests, including D-dimer, and any drip or cannula
- The scan fee and the radiologist's reporting fee
- What happens, and what it costs, if a clot is confirmed and treatment is needed
- What happens if the result is inconclusive and a further test is required
- Follow-up appointments and review of how long treatment continues
- A clear statement that genuine emergencies will be redirected to NHS emergency care
On the NHS? Assessment for suspected PE is emergency NHS care delivered through A&E, acute medicine and same-day emergency care. Private same-day medicine may help investigate stable, lower-risk problems quickly, but it is never a substitute for emergency care when a clot is suspected.
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
- Not explaining that genuine emergencies must go to 999/A&E rather than a private booking.
- Ordering a D-dimer or CTPA without explaining what the result will actually change.
- Not discussing radiation, contrast and incidental findings before a CTPA.
- Starting a blood thinner without explaining bleeding risk and how the decision will be reviewed.
- Implying a normal result guarantees nothing is wrong, without explaining other possible causes.
Marketing red flags
- Any private service offering to assess sudden chest pain or breathlessness instead of directing you to emergency care.
- Routine D-dimer or CT 'clot checks' marketed to people without symptoms.
- Promising a scan will 'definitely rule out' a clot, ignoring false negatives and timing.
- Downplaying radiation, contrast risk or incidental findings to sell a scan.
Choosing a specialist safely
- Check the specialist 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 specialist 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 specialist will welcome every one of these.
- Based on my clot score, do I actually need a scan, or can a D-dimer rule this out safely?
- Which scan are you choosing for me (CTPA or V/Q), and why?
- What will this result change about my treatment?
- If you are starting a blood thinner before the result, when and how will that be reviewed?
- If a clot is confirmed, how long will I need treatment and why?
- If a clot is ruled out, what else might be causing my symptoms and when should I come back?
- 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 specialist who carries out my test, 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 test 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
Should I book a private appointment if I think I have a clot on the lung?
What is a D-dimer test and why isn't it enough on its own?
Is the CT scan safe? It uses radiation and dye.
Why might I be given a blood thinner before the scan result?
Can a scan miss a clot or find one that doesn't matter?
I'm pregnant — is the assessment different?
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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: NHS — Pulmonary embolism NICE NG158 — Venous thromboembolic diseases: diagnosis and management NICE NG158 — full guideline (PDF) Overdiagnosis of pulmonary embolism: definition, causes and implications (PMC) Diagnostic yield and renal complications after CTPA (PMC) RESPECT-ED: rates of PE and subsegmental PE on modern CTPA (PMC)
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.
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