Recognising, diagnosing and treating blood clots in the lungs
Pulmonary Embolism: Causes, Treatment and Answers to Common Questions
A pulmonary embolism occurs when a blood clot blocks one or more arteries in the lungs. It can range from a small, stable clot to a life-threatening obstruction that places severe strain on the heart. Rapid recognition and appropriate anticoagulant treatment can be lifesaving.
- PE symptoms
- Deep vein thrombosis
- Risk factors
- D-dimer
- CT pulmonary angiography
- Anticoagulants
- Recovery
- Air travel
Most pulmonary emboli begin as a DVT
A clot commonly forms in a deep vein of the leg or pelvis. Part of the clot may break away, pass through the right side of the heart and lodge in the pulmonary arteries.
Symptoms may be subtle
A normal oxygen saturation, normal chest examination or absence of leg swelling does not reliably exclude pulmonary embolism.
What is a pulmonary embolism?
A pulmonary embolism, commonly shortened to PE, is a blockage in one or more pulmonary arteries. In most cases, the blockage is caused by a blood clot that has travelled from a deep vein in the leg or pelvis.
The word pulmonary refers to the lungs, while an embolus is material that travels through the circulation and becomes lodged in a blood vessel.
A PE reduces blood flow through part of the lungs. This can interfere with oxygen exchange and increase the pressure against which the right side of the heart must pump.
The effects vary considerably. A small embolus may cause limited symptoms, whereas a large or strategically placed clot may cause shock, severe right-heart strain or cardiac arrest.
Deep vein thrombosis
A thrombus forms in a deep vein, usually in the leg or pelvis. The clot may remain in place or partially detach.
Embolisation
A detached fragment travels through the venous circulation and reaches the right side of the heart.
Pulmonary-artery obstruction
The embolus becomes lodged in a pulmonary artery and reduces blood flow through part of the lung.
Right-heart strain
A large obstruction can abruptly increase pulmonary pressure and impair the ability of the right ventricle to pump blood.
Deep vein thrombosis and pulmonary embolism are collectively called venous thromboembolism, or VTE.
Symptoms of pulmonary embolism
PE symptoms depend on the size and location of the clot, underlying heart and lung health and the body’s cardiovascular response. Symptoms may develop suddenly or more gradually.
Sudden breathlessness
Difficulty breathing may appear abruptly, worsen on exertion or occur without an obvious respiratory infection.
Pleuritic chest pain
Pain is often sharp and worse when breathing in, coughing or moving the chest.
Coughing up blood
Haemoptysis may occur when a peripheral embolus causes inflammation or infarction near the lining of the lung.
Fast heartbeat
Tachycardia may reflect pain, low oxygen, reduced cardiac output or the body’s response to circulatory strain.
Dizziness or fainting
Light-headedness, collapse or loss of consciousness can occur when a PE significantly reduces blood flow from the heart.
Unexplained low oxygen
Oxygen saturation may fall, although some people with PE retain a normal reading.
Upper-back or shoulder pain
Pleural irritation can occasionally cause pain outside the central chest.
Anxiety or a sense of danger
Acute breathlessness and cardiovascular stress may produce intense anxiety, but symptoms should not be dismissed as panic.
A pulmonary embolism can occur without classic symptoms
Some patients have only mild breathlessness, unexplained fatigue, a fast heartbeat or a decline in exercise tolerance. Others have no obvious symptoms of DVT in the legs.
Sudden pleuritic pain and breathlessness are also discussed in the guide to respiratory and pleuritic causes of chest pain .
Symptoms of deep vein thrombosis
A DVT commonly affects one leg, but symptoms may be mild or absent. Bilateral swelling is more often caused by another condition, although clinical assessment remains important.
One-sided swelling
The calf, ankle, thigh or whole leg may become noticeably more swollen than the other side.
Calf or thigh pain
Pain may feel like cramping, tenderness, heaviness or an ache that is not explained by an injury.
Warmth
Skin over the affected area may feel warmer than the corresponding area on the other leg.
Colour change
Redness, darker discolouration or a bluish appearance may occur, although colour may remain normal.
Do not use Homan’s sign to check for DVT
Flexing the foot to see whether it causes calf pain is unreliable and cannot confirm or exclude a blood clot. Suspected DVT requires a formal clinical assessment and, where indicated, ultrasound.
What causes pulmonary embolism?
Clots become more likely when one or more elements of Virchow’s triad are present: reduced blood flow, injury to the vessel wall and increased tendency of the blood to clot.
Reduced blood flow
Immobility
Bed rest, hospital admission, paralysis, a plaster cast or a long journey can reduce movement of blood through the legs.
Surgery
Major surgery, particularly involving the pelvis, abdomen, hip or knee, can combine immobility with tissue injury.
Serious illness
Infection, heart failure, stroke and critical illness can substantially limit mobility.
Vessel-wall injury
Trauma
Fractures and major soft-tissue injuries can damage blood vessels and activate clotting.
Operations
Surgical injury activates inflammatory and coagulation pathways during the recovery period.
Venous devices
Central venous catheters can increase the risk of upper-limb or central venous thrombosis.
Increased clotting tendency
Cancer
Active malignancy and some cancer treatments increase the activation of coagulation.
Hormonal factors
Combined hormonal contraception, hormone replacement therapy, pregnancy and the postnatal period can raise risk.
Inherited thrombophilia
Conditions such as factor V Leiden may increase clotting tendency, although testing is not required for every PE.
Important risk factors
Previous DVT or PE
A previous venous thromboembolism increases the risk of a future event, particularly after anticoagulation has stopped.
Recent surgery or admission
Risk may remain elevated after leaving hospital, especially after major orthopaedic or cancer surgery.
Active cancer
Cancer may activate coagulation, restrict mobility and require treatments that further increase thrombosis risk.
Pregnancy and postpartum period
Hormonal change, reduced venous flow and delivery-related factors increase risk during pregnancy and after childbirth.
Oestrogen-containing medicines
Combined contraception and some forms of hormone replacement therapy increase VTE risk.
Prolonged immobility
Reduced movement from illness, disability, a cast or a journey lasting several hours may contribute.
Obesity
Higher body weight is associated with venous stasis, inflammation and increased VTE risk.
Increasing age
VTE becomes more common with age, partly because of frailty, illness, cancer and reduced mobility.
Smoking
Smoking contributes to vascular inflammation and commonly clusters with other cardiovascular risks.
COVID-19 and severe infection
Acute inflammatory illness can activate coagulation and increase thrombosis risk, particularly during hospitalisation.
Provoked and unprovoked PE
A provoked PE follows a recognised temporary or persistent risk factor, such as surgery, immobility, pregnancy or cancer. An unprovoked PE occurs without a clear major trigger. This distinction influences recurrence assessment and the duration of anticoagulation.
How is pulmonary embolism diagnosed?
No single symptom, examination finding or routine blood test can diagnose PE. Clinicians combine the history, observations, clinical probability and appropriate imaging.
- Assess clinical stability Blood pressure, heart rate, respiratory rate, oxygen saturation, mental state and signs of shock are reviewed immediately.
- Estimate clinical probability A validated score such as the two-level PE Wells score may be used alongside clinical judgement.
- Consider PERC only in suitable low-risk patients The pulmonary embolism rule-out criteria may help avoid testing when overall clinical suspicion is already low.
- Use D-dimer when appropriate A negative D-dimer can help exclude PE in selected patients with low or unlikely clinical probability.
- Perform CT pulmonary angiography CTPA directly examines the pulmonary arteries and is the main diagnostic scan for many adults.
- Use alternative imaging when needed A ventilation-perfusion scan may be preferred when contrast, radiation distribution or another clinical consideration makes CTPA unsuitable.
- Assess the legs Compression ultrasound may identify a proximal DVT and can be particularly useful when leg symptoms are present.
- Evaluate cardiac strain ECG, cardiac troponin, BNP or NT-proBNP and echocardiography may help assess severity rather than confirm every PE.
| Test | What it contributes | Important limitation |
|---|---|---|
| D-dimer | Helps exclude PE in selected patients with low or unlikely clinical probability | Frequently raised by infection, surgery, pregnancy, cancer and increasing age |
| CT pulmonary angiography | Directly visualises emboli in the pulmonary arteries | Involves radiation and iodinated contrast |
| Ventilation-perfusion scan | Compares ventilation with pulmonary blood flow | May be non-diagnostic when substantial underlying lung disease is present |
| Leg-vein ultrasound | Detects proximal DVT | A negative leg scan does not independently exclude PE |
| Chest X-ray | Identifies pneumonia, pneumothorax and other alternative causes | Often normal or non-specific in PE |
| ECG | Assesses rhythm, cardiac strain and alternative cardiac diagnoses | May be normal and cannot exclude PE |
| Blood gas | Assesses oxygenation, ventilation and severity in selected patients | Normal results do not exclude PE |
| Echocardiography | Assesses right-heart strain in severe or unstable PE | A normal echocardiogram does not exclude a smaller PE |
D-dimer should not be used as a stand-alone screening test
A raised result is non-specific. It should be ordered and interpreted within a validated diagnostic pathway rather than used indiscriminately in every patient with chest symptoms.
How is the severity of a pulmonary embolism assessed?
The seriousness of a PE is not determined only by the clot’s size on a scan. Blood pressure, heart function, biomarkers, oxygen requirement, comorbidity and clinical stability are also critical.
Haemodynamically unstable PE
Clinical pattern
Shock, persistent low blood pressure, severe circulatory compromise or cardiac arrest.
Main concern
The right ventricle cannot maintain adequate blood flow through the obstructed pulmonary circulation.
Management
Emergency resuscitation and reperfusion treatment may be needed in addition to anticoagulation.
Intermediate-risk PE
Clinical pattern
Blood pressure remains stable, but right-heart strain or raised cardiac biomarkers may be present.
Main concern
Some patients may deteriorate and therefore require monitored hospital care.
Management
Anticoagulation is standard, with escalation if cardiovascular instability develops.
Low-risk PE
Clinical pattern
Stable observations, low predicted short-term risk and no major reason for inpatient treatment.
Assessment
Tools such as PESI, simplified PESI or Hestia criteria may support clinical judgement.
Management
Selected patients may receive outpatient treatment with reliable follow-up and clear safety-netting.
How is pulmonary embolism treated?
Anticoagulation is the main treatment for most pulmonary emboli. It prevents existing clots from enlarging and reduces the formation of new clots while the body gradually breaks down the embolus.
Direct oral anticoagulants
Apixaban or rivaroxaban can be started directly in many haemodynamically stable adults, subject to kidney function, interactions and individual suitability.
Low-molecular-weight heparin
LMWH may be used initially or longer term in pregnancy, selected cancer-associated thrombosis or when oral treatment is unsuitable.
Unfractionated heparin
Intravenous heparin may be preferred when rapid reversal, procedures, severe renal impairment or haemodynamic instability are relevant.
Warfarin
Warfarin remains appropriate in selected situations and requires regular INR monitoring and initial heparin overlap.
Systemic thrombolysis
Clot-dissolving treatment may be used for haemodynamically unstable PE when the expected benefit outweighs major bleeding risk.
Catheter-directed treatment
Specialist teams may use catheter-delivered thrombolysis, aspiration or mechanical thrombectomy in selected severe cases.
Surgical embolectomy
Emergency surgical removal may be considered when other reperfusion treatments are unsuitable or unsuccessful.
Inferior vena cava filter
An IVC filter is reserved for selected situations, particularly when anticoagulation is contraindicated. It is not routine treatment for most PE.
Thrombolysis is not routine treatment for every PE
Thrombolytic medicines can cause major or intracranial bleeding. Their strongest indication is PE causing haemodynamic instability, shock or cardiac arrest, with case-specific decisions in other deteriorating patients.
How long is anticoagulation continued?
Confirmed PE is generally treated for at least three months. Treatment duration after that point depends on why the clot occurred and the balance between recurrence and bleeding risk.
| Clinical situation | Possible approach | Key consideration |
|---|---|---|
| Major temporary provoking factor | Anticoagulation may stop after the initial treatment period when the provoking factor has resolved | Examples include major surgery or substantial temporary immobility |
| Unprovoked PE | Extended or indefinite anticoagulation may be considered | Recurrence risk is weighed against bleeding risk and patient preference |
| Persistent risk factor | Longer treatment is often required | Examples include active cancer or continuing major immobility |
| Recurrent VTE | Long-term anticoagulation is frequently recommended | The cause, treatment adherence and bleeding history are reviewed |
| High bleeding risk | Duration or drug choice may need modification | Decisions require individual specialist assessment |
Do not stop an anticoagulant without medical advice
Missing doses or stopping early can increase the risk of recurrent PE. This is particularly important with direct oral anticoagulants, which have a relatively short duration of action after a dose is missed.
Living safely with anticoagulant treatment
Take doses consistently
Follow the prescribed timing carefully and ask the anticoagulant service what to do after a missed dose.
Check interactions
Prescription drugs, over-the-counter medicines and herbal products can alter anticoagulant effect or bleeding risk.
Tell healthcare professionals
Dentists, surgeons, pharmacists and emergency clinicians need to know which anticoagulant you take.
Avoid unnecessary NSAIDs
Ibuprofen, naproxen and similar medicines can increase bleeding risk unless specifically approved.
Attend monitoring
Kidney function, liver function, blood count or INR monitoring may be required depending on the drug.
Carry treatment information
Keep an anticoagulant alert card or digital medication record available.
Seek urgent advice for possible serious bleeding
- vomiting blood or material resembling coffee grounds;
- black, tar-like stools or significant rectal bleeding;
- blood in the urine that persists or is substantial;
- a severe or unusual headache;
- head injury while taking anticoagulants;
- uncontrolled bleeding;
- sudden weakness, speech disturbance or confusion;
- significant unexplained bruising with illness or weakness.
Recovery after pulmonary embolism
Many people recover well after a PE, but improvement is not always immediate. Breathlessness, chest discomfort, fatigue and reduced confidence during activity may persist for weeks or months.
Gradual return to activity
Gentle walking and ordinary movement are generally encouraged once the patient is medically stable, with progression guided by symptoms and clinical advice.
Residual chest pain
Pleuritic inflammation or a small pulmonary infarction can cause pain after treatment has begun.
Fatigue
The acute illness, hospital admission, deconditioning, sleep disruption and anxiety can all contribute to prolonged fatigue.
Emotional recovery
Fear of recurrence is common. Clear follow-up advice and a graded return to normal activity can improve confidence.
Persistent breathlessness may require a structured specialist breathlessness assessment rather than being attributed automatically to the previous clot.
What if breathlessness persists?
Persistent symptoms have several possible explanations, including deconditioning, anxiety, unresolved pleural pain, underlying lung disease, heart disease or a less common pulmonary vascular complication.
Residual thrombus
Some clot material may remain visible after treatment without necessarily causing major physiological impairment.
Chronic thromboembolic pulmonary hypertension
CTEPH occurs when organised clot and vascular remodelling cause persistent pulmonary hypertension. It is uncommon but potentially treatable.
Post-PE syndrome
Some patients have continuing breathlessness or reduced exercise capacity despite no major pulmonary hypertension.
Another diagnosis
Asthma, COPD, anaemia, cardiac disease and breathing pattern dysfunction may coexist with or become apparent after PE.
Worsening symptoms require reassessment
New or worsening breathlessness, chest pain, haemoptysis, leg swelling or collapse should not be assumed to be part of normal recovery. Recurrent PE and other complications must be considered.
Can you fly after a pulmonary embolism?
Current British Thoracic Society guidance advises delaying air travel, where possible, for at least two weeks after an acute PE. The patient should be clinically stable and should receive individual advice from the treating team before flying.
The appropriate interval may be longer after a severe PE, persistent low oxygen, right-heart strain, recent surgery, ongoing bleeding or another complication.
- Obtain medical clearance Confirm that symptoms, oxygen levels, cardiovascular status and anticoagulant treatment are stable.
- Carry anticoagulants in hand luggage Keep enough medicine for the journey and additional doses in case of delay.
- Maintain the dosing schedule Plan around time-zone changes and obtain advice when the interval between doses may be affected.
- Move regularly Walk when safe and flex the ankles, feet and calves while seated, particularly on journeys lasting more than four hours.
- Drink water regularly Avoid dehydration and limit excessive alcohol and caffeine.
- Wear loose clothing Avoid restrictive clothing around the waist or legs.
- Use compression stockings only when advised Correctly fitted below-knee graduated stockings may be appropriate for selected travellers.
- Carry clinical information Bring a medication list, anticoagulant alert card and relevant medical letter.
Do not add extra anticoagulant doses before flying
A person already taking therapeutic anticoagulation should not take additional LMWH or extra oral anticoagulant unless this has been specifically prescribed. Extra dosing can cause serious bleeding.
Reducing the risk of another pulmonary embolism
Complete anticoagulant treatment
Take the prescribed course and attend the planned review before any decision to stop or reduce treatment.
Stay mobile
Avoid unnecessary prolonged immobility and follow mobilisation advice after illness or surgery.
Use hospital prophylaxis
Preventive anticoagulation may be offered during hospital admission or after selected operations.
Review hormonal medicines
Discuss contraception or hormone therapy after VTE because some oestrogen-containing products may no longer be appropriate.
Stop smoking
Smoking cessation improves vascular, cardiac and respiratory health and reduces several overlapping risks.
Address persistent risk factors
Cancer, inflammatory illness, reduced mobility and body weight may require longer-term risk-management plans.
People who smoke can read answers to common questions about stopping smoking .
Do you need cancer or thrombophilia testing?
Extensive testing is not automatically required after every PE. Investigations depend on age, history, examination, whether the clot was provoked and whether the result would change management.
Cancer assessment
Clinical history, examination and routine age-appropriate screening are important. Additional investigation is guided by symptoms or abnormal findings.
Thrombophilia testing
Testing may be considered in selected unprovoked or familial cases but is not useful routinely while anticoagulation is continuing.
Antiphospholipid syndrome
Testing may matter when an unprovoked clot, recurrent thrombosis, pregnancy morbidity or another compatible feature is present.
Family testing
Relatives are not routinely screened unless a specific clinically important inherited condition has been identified.
When should medical help be sought?
Call 999 immediately for:
- severe or rapidly worsening breathlessness;
- chest or upper-back pain with significant breathing difficulty;
- a very fast heartbeat with weakness or chest pain;
- collapse, fainting or inability to respond normally;
- blue or grey lips or skin;
- new confusion or extreme drowsiness;
- coughing up a substantial amount of blood;
- suspected cardiac arrest.
Do not drive yourself to hospital. Call an ambulance.
Seek urgent same-day advice for:
- new sudden breathlessness;
- new pleuritic chest pain;
- coughing up any unexplained blood;
- new one-sided leg swelling or pain;
- worsening symptoms while taking anticoagulants;
- signs of clinically important bleeding;
- persistent symptoms after recent surgery, hospitalisation or travel.
Conclusion
Pulmonary embolism occurs when a clot, usually originating in a deep vein of the leg or pelvis, travels to and obstructs the pulmonary circulation.
Symptoms may include sudden breathlessness, pleuritic chest pain, coughing up blood, a fast heartbeat, dizziness or collapse. However, symptoms can be subtle and a normal oxygen saturation does not exclude PE.
Diagnosis combines clinical probability, D-dimer testing where appropriate and imaging such as CT pulmonary angiography.
Anticoagulation is the main treatment and is generally continued for at least three months. Thrombolysis, catheter-directed treatment or surgery is reserved mainly for severe or deteriorating cases.
Air travel should usually be postponed for at least two weeks after an acute PE and resumed only when the patient is clinically stable and has obtained individual medical advice.
Persistent breathlessness, chest pain or reduced exercise tolerance after treatment may justify a specialist respiratory and pulmonary vascular assessment .
Frequently asked questions
What are the most common symptoms of pulmonary embolism?
Common symptoms include sudden breathlessness, sharp chest pain that worsens during inspiration, a fast heartbeat and coughing up blood. Some people have milder or less typical symptoms.
Can pulmonary embolism be fatal?
Yes. A large PE can cause severe right-heart failure, shock or cardiac arrest. Prompt diagnosis and treatment substantially improve the likelihood of recovery.
Can I have a PE with normal oxygen levels?
Yes. Oxygen saturation may remain normal, particularly with smaller emboli or good underlying cardiopulmonary reserve.
Can I have a pulmonary embolism without leg swelling?
Yes. Many patients with PE have no obvious leg symptoms, and the original DVT may no longer be detectable.
Does a high D-dimer confirm PE?
No. D-dimer rises in many conditions. It is mainly useful for excluding PE in selected patients with low or unlikely clinical probability.
Does a normal chest X-ray exclude pulmonary embolism?
No. The chest X-ray may be normal. It is mainly useful for identifying alternative explanations such as pneumonia or pneumothorax.
How quickly do blood thinners dissolve the clot?
Anticoagulants do not directly dissolve the clot. They prevent enlargement and new clot formation while the body gradually breaks down the embolus over time.
How long must I take anticoagulants?
Treatment usually lasts at least three months. Longer or indefinite treatment may be recommended after an unprovoked, recurrent or persistently provoked PE.
Can I exercise after pulmonary embolism?
Gentle movement is generally encouraged once medically stable. Exercise should be increased gradually and adapted after a severe PE, ongoing symptoms or right-heart strain.
Can I fly after a PE?
BTS guidance advises delaying flying for at least two weeks where possible. Travel should resume only after individual medical review confirms clinical stability.
Should I take an extra blood thinner before a flight?
No, not unless specifically prescribed. Additional anticoagulation can cause serious bleeding.
Can pulmonary embolism come back?
Yes. Recurrence risk depends on whether the original clot was provoked, whether risk factors persist and whether anticoagulation is continued.
What is chronic thromboembolic pulmonary hypertension?
CTEPH is persistent pulmonary hypertension caused by organised clot and pulmonary-artery obstruction after PE. It is uncommon but should be considered when breathlessness does not improve.
Does everyone need thrombophilia testing?
No. Testing is reserved for selected cases where the result could change treatment or advice to the patient or family.
References and further information
- National Institute for Health and Care Excellence. Venous thromboembolic diseases: diagnosis, management and thrombophilia testing. NICE guideline NG158. View the NICE VTE guideline
- NHS. Pulmonary embolism. View NHS pulmonary-embolism information
- British Thoracic Society. BTS Clinical Statement on air travel for passengers with respiratory disease. View the BTS air-travel statement
- London Chest Specialist. Chest-pain diagnosis and treatment. Read about specialist chest-pain assessment
- London Chest Specialist. Breathlessness diagnosis and treatment. Read about specialist breathlessness assessment
- London Chest Specialist. Lung-function tests. Read about respiratory diagnostic testing
- London Chest Specialist. Smoking cessation: questions answered. Read the smoking-cessation guide
- London Chest Specialist. Causes of chest pain: respiratory, cardiac, gastroenterological or musculoskeletal? Read the chest-pain causes guide
