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Pulmonary embolism

Medical Professionals

Professional Reference articles are designed for health professionals to use. They are written by UK doctors and based on research evidence, UK and European Guidelines. You may find the Pulmonary embolism article more useful, or one of our other health articles.

Important information

Pulmonary embolism (PE) is a medical emergency. It may present with very few clinical signs and/or symptoms, making it easy to miss, and a high index of suspicion is warranted.

PE results from obstruction within the pulmonary arterial tree. The emboli can be caused by:

  • Thrombosis - accounts for the majority of cases and has usually arisen from a distant vein and travelled to the lungs via the venous system.

  • Fat - following long bone fracture or orthopaedic surgery.

  • Amniotic fluid1 .

  • Air - following neck vein cannulation or bronchial trauma.

The rest of this article deals with thrombotic PE.

Continue reading below


The incidence of pulmonary embolism in the UK varies from 7-8 per 10,000 people2 .

Risk factors3

Clots form when one or more of the following factors are present: increased blood coagulability, reduced mobility or blood vessel abnormalities. These correspond to some of the risk factors for VTE (see below). A number of patients may not have any risk factors, making the diagnosis difficult.

Major risk factors: relative risk of 5-20


  • Major abdominal/pelvic surgery or hip/knee replacement (risk lower if prophylaxis used).

  • Postoperative intensive care.


  • Late pregnancy.

  • Puerperium.

  • Caesarean section.

Lower-limb problems:

  • Fracture.

  • Varicose veins - previous varicose vein surgery; superficial thrombophlebitis; varicose veins per se are not a risk factor.


  • Abdominal/pelvic.

  • Advanced/metastatic.

Reduced mobility:

  • Hospitalisation.

  • Institutional care.

Previous proven VTE:

  • Intravenous (IV) drug use (could be major or minor risk factor: no data on relative risk).


  • Major trauma.

  • Spinal cord injury.

  • Central venous lines.

Minor risk factors: relative risk of 2-4


  • Congenital heart disease.

  • Congestive cardiac failure.

  • Hypertension.

  • Paralytic stroke.


  • Pregnancy (but see major risk factors for late pregnancy and puerperium).

  • Combined oral contraceptive.

  • Hormone replacement therapy.


  • Thrombotic disorders (a detailed list is available). Consider this in cases of PE aged <40 years, recurrent VTE or a positive family history.

  • Myeloproliferative disord


  • Nephrotic syndrome.

  • Chronic dialysis.

  • Paroxysmal nocturnal haemoglobinuria.


  • Chronic obstructive pulmonary disease (COPD).

  • Neurological disability.

  • Occult malignancy.

  • Long-distance sedentary travel.

  • Obesity.

  • Other chronic diseases: inflammatory bowel disease, Behçet's disease.

Continue reading below


The symptoms and signs of PE are not specific. Severe cases of PE can lead to collapse or sudden death. Some PEs are rapidly fatal. In the majority of the fatal cases the PE is not clinically diagnosed prior to death.

Symptoms include:

  • Dyspnoea.

  • Pleuritic chest pain, retrosternal chest pain.

  • Cough and haemoptysis.

  • Any chest symptoms in a patient with symptoms suggesting a deep vein thrombosis (DVT).

  • In severe cases, right heart failure causes dizziness or syncope.

Signs include:

  • Tachypnoea, tachycardia.

  • Hypoxia, which may cause anxiety, restlessness, agitation and impaired consciousness.

  • Pyrexia.

  • Elevated jugular venous pressure.

  • Gallop heart rhythm, a widely split second heart sound, tricuspid regurgitant murmur.

  • Pleural rub.

  • Systemic hypotension and cardiogenic shock.

Differential diagnosis

Other causes of collapse, chest pain or dyspnoea - importantly:

Continue reading below


NB: treatment may precede investigations if the patient is very ill (see 'Initial management' below).

National Institute for Health and Care Excellence (NICE) recommendations

  • If a patient presents with signs or symptoms of PE, carry out an assessment of their general medical history, a physical examination and CXR to exclude other causes.

  • If clinical suspicion for PE is low, use the pulmonary embolus rule-out criteria to determine if further investigation of PE is indicated5 .

  • If PE is suspected, use the two-level PE Wells' score to estimate the clinical probability of PE (see below).

  • Offer patients in whom PE is suspected and with a likely two-level PE Wells' score (more than 4 points) an immediate computerised tomography pulmonary angiogram (CTPA).

  • If a CTPA cannot be carried out immediately or is contra-indicated, offer immediate interim parenteral anticoagulant therapy followed by a CTPA,

  • Consider a proximal leg vein ultrasound scan if the CTPA is negative and DVT is suspected. If the scan is negative consider alternative diagnoses but ensure the person is aware of the signs and symptoms of PE and that they should seek immediate medical help if these develop.

  • Offer patients in whom PE is suspected and with a two-level PE Wells' score less than 4 points a D-dimer test with rhe result available within four hours if possible. If the result is not available within four hours, offer interim therapeutic anticoagulation.

  • If the result is positive, offer either an immediate CTPA or immediate interim parenteral anticoagulant therapy followed by a CTPA, if a CTPA cannot be carried out immediately.

  • If the result is negative, stop immediate interim anticoagulation, consider alternative diagnoses and warn patients to look out for the signs and symptoms of PE.

  • For patients who have an allergy to contrast media, or who have severe renal impairment (estimated creatinine clearance less than 30 ml/min), or whose risk from irradiation is high:

    • Assess the suitability of a ventilation/perfusion single-photon emission computerised tomography (V/Q SPECT) scan or, if a V/Q SPECT scan is not available, a V/Q planar scan, as an alternative to CTPA.

    • If offering a V/Q SPECT or planar scan that will not be available immediately, offer immediate interim parenteral anticoagulant therapy.

  • Diagnose PE and treat patients with a positive CTPA or in whom PE is identified with a V/Q SPECT or planar scan. Offer or continue anticoagulation treatment, or if anticoagulation treatment is contra-indicated, consider a mechanical intervention.

  • Consider alternative diagnoses in the following two groups of patients:

    • Patients with an unlikely two-level PE Wells' score and either a negative D-dimer test, or a positive D-dimer test and a negative CTPA.

    • Patients with a likely two-level PE Wells' score and both a negative CTPA and no suspected DVT.

  • Offer all patients diagnosed with unprovoked PE (defined as PE in a person with no recent major clinical risk factor for PE, who is not taking the combined oral contraceptive pill or hormone replacement therapy), who are not already known to have cancer the following investigations for cancer:

    • Physical examination guided by a full and thorough history.

    • CXR.

    • Blood tests (FBC, renal function, serum calcium, PT and APTT, and LFTs).

    • Urinalysis.

  • Consider further investigations for cancer with an abdomino-pelvic CT scan (and a mammogram for women) in all patients aged over 40 years with a first unprovoked PE who do not have signs or symptoms of cancer based on initial investigation.

  • Consider testing for antiphospholipid antibodies in patients who have had unprovoked PE if it is planned to stop anticoagulation treatment. Be aware that these tests can be affected by anticoagulants and be prepared to seek specialist advice if indicated.

  • Consider testing for hereditary thrombophilia in patients who have had unprovoked PE and who have a first-degree relative who has had DVT or PE, if it is planned to stop anticoagulation treatment.

Risk score

Assessment of the clinical probability of VTE is recommended, as it is relevant when interpreting clinical findings and deciding how to investigate. NICE recommends the Wells' score but other scoring systems have also been developed.

Wells' Two-level PE Score

Clinical feature


Clinically suspected DVT (minimum leg swelling and pain on palpation of deep veins).

Alternative diagnosis less likely than PE.

Tachycardia (heart rate above 100 beats per minute).

Immobilisation for more than three days or surgery in the previous four weeks.

History of DVT or PE.


Malignancy (on treatment in the preceding six months or palliative stage).








Clinical probability

  • 4 points or fewer = PE unlikely.

  • More than 4 points = PE likely.

For patients with a score of 4 points or fewer, use the PERC rule.


General investigations6

  • Baseline investigations - as for any ill patient: oxygen saturation, FBC, biochemistry, baseline clotting screen. Troponin and brain natriuretic peptide levels may also be elevated.

  • ECG - may be normal, or show any of these changes: sinus tachycardia, atrial fibrillation, nonspecific ST or T-wave abnormalities, right ventricular strain pattern V1-3, right axis deviation, right bundle branch block (RBBB), or deep S-waves in I with Q waves in III and inverted T waves in III ('S1,Q3,T3' pattern). A large PE can show ECG features of acute cardiac ischaemia (eg, ST depression)7 .

  • CXR - mainly useful to exclude other chest disease, and is needed for interpreting V/Q scans. It is usually normal, but may show: decreased vascular markings, atelectasis or a small pleural effusion. An occasional late sign may be an homogeneous wedge-shaped area of pulmonary infarction in the lung periphery (Hampton's hump) with its base contiguous to a visceral pleural surface and its rounded convex apex directed toward the hilum.

  • Arterial blood gases - may show reduced PaO2, reduced PaCO2 due to hyperventilation or acidosis.

  • Echocardiography - may show thrombus in proximal pulmonary arteries and, if normal, can exclude haemodynamically important PE. It cannot exclude smaller PEs. It may show signs of right ventricular strain or right ventricular hypokinesis.

  • Cardiac troponins - can be indicative of right heart strain.

  • D-dimers - fibrin D-dimer is a degradation product of cross-linked fibrin. The concentration increases in patients with acute VTE and provides a very sensitive test to exclude acute DVT or PE. D-dimer tests have less specificity and are less useful in some groups of patients - eg, those with high clinical probability; those admitted to hospital for another reason, in whom the suspicion of PE is raised during their hospital stay; individuals older than 65 years; pregnant women8 .

Specific investigations for VTE4 6

The choice and order of investigations will depend on the clinical likelihood of PE, how ill the patient is and availability of the test. The 'gold standard' test is CTPA. An explanation of the scope of each test helps in understanding these strategies:

  • Leg ultrasound: in patients with co-existing clinical DVT, lower-limb ultrasound as the initial imaging test is often sufficient to confirm VTE - and hence to start anticoagulation. However, a singe normal leg ultrasound cannot exclude DVT.

  • CTPA has become the method of choice for imaging the pulmonary vasculature in patients with suspected PE.

  • Isotope lung scanning (V/Q scan): although there have been controversies about the accuracy of isotope scans, they are reliable enough to exclude or confirm PE, if performed according to UK protocols. However, if the result is 'indeterminate', further imaging is needed. For this reason, V/Q scanning is reserved for patients in whom CTPA is contra-indicated.

It is important to appreciate that, although there are risk scores and various D-dimer assays available, clinical suspicion of VTE may still need to be followed up when these results are negative. The PERC rule is useful in this situation, but even then the safest course is to adopt a low threshold to discuss the case further with respiratory physicians and radiologists.


Initial resuscitation

  • Oxygen 100%.

  • Obtain IV access, monitor closely, start baseline investigations.

  • Give analgesia if necessary (eg, morphine).

  • Assess circulation: suspect massive PE if systolic BP is <90 mm Hg or there is a fall of 40 mm Hg, for 15 minutes, not due to other causes.

Anticoagulation therapy4

  • Outpatient anticoagulation may be considered for patients with low-risk PE, providing they are supplied with all the necessary information.

  • Offer anticoagulation to patients with confirmed PE for at least three months.

  • If not already available, arrange baseline investigations (see above).

  • Offer apixaban or rivaroxaban to patients with confirmed PE2 .

    • If neither of these is suitable offer a choice of low molecular weight heparin (LMWH) for five days followed by dabigatran or edoxaban; or

    • LMWH concurrently with a vitamin K antagonist (VKA) for at least five days, or until the INR is at least 2.0 in two consecutive readings, followed by a VKA on its own.

  • Offer people with confirmed PE and renal impairment (estimated creatinine clearance between 15 ml/min and 50 ml/min) one of:

    • Apixaban.

    • Rivaroxaban.

    • LMWH for at least five days followed by edoxaban or dabigatran if estimated creatinine clearance is 30 ml/min or above.

    • LMWH or UFH, given concurrently with a VKA for at least five days or until the INR is at least 2.0 in two consecutive readings, followed by a VKA on its own.

  • Offer people with confirmed PE and renal failure (estimated creatinine clearance less than 15 ml/min) one of:

    • LMWH.

    • UFH.

    • LMWH or UFH concurrently with a VKA for at least five days or until the INR is at least 2.0 in two consecutive readings, followed by a VKA on its own.

  • Consider anticoagulation for people with PE who have extreme body weight (less than 50 kg or more than 120 kg) but ensure regular monitoring and dosage adjustment as per manufacturer's instructions and local protocols. Offer people with confirmed PE and an established diagnosis of triple positive antiphospholipid syndrome LMWH concurrently with a VKA for at least five days, or until the INR is at least 2.0 in two consecutive readings, followed by a VKA on its own.

  • People with confirmed PE and an established diagnosis of triple positive antiphospholipid syndrome should be offered LMWH concurrently with a VKA for at least five days, or until the INR is at least 2.0 in two consecutive readings, followed by a VKA on its own.

  • Offer a direct-acting oral anticoagulant (DOAC) to patients with active cancer (receiving active antimitotic treatment; or diagnosed within the previous six months; or recurrent or metastatic; or inoperable) and confirmed PE, and continue for six months. At six months, assess the risks and benefits of continuing anticoagulation. Take into account the tumour site, interactions with other drugs, including those used to treat cancer, and the person's bleeding. If a DOAC is unsuitable, consider LMWH alone or LMWH concurrently with a VKA[5] for at least five days, or until the INR is at least 2.0 in two consecutive readings, followed by a VKA on its own.

  • Offer a vitamin K antagonist (VKA) to patients with confirmed PE within 24 hours of diagnosis and continue the VKA for three months. At three months, assess the risks and benefits of continuing VKA treatment.

  • Offer a VKA beyond three months to patients with an unprovoked PE, taking into account the patient's risk of VTE recurrence and whether they are at increased risk of bleeding.

Provide patients who are having anticoagulation treatment with an anticoagulant information booklet and an anticoagulant alert card and advise them to carry the anticoagulant alert card at all times.

Editor's note

Dr Sarah Jarvis, 17th September 2021

NICE quality standard on VTE in adults
NICE has issued a new quality standard9 - elements relevant to PE include:

Over-16s in hospital who are assessed as needing VTE prophylaxis should have it started as soon as possible and not longer than 14 hours after admission.

Over-16s discharged with lower-limb immobilisation should be assessed to identify their risk of VTE.

Over-18s taking anticoagulation treatment after a VTE should have a review at three months and then at least once a year if they continue to take it long term.

Over-18s having outpatient treatment for suspected or confirmed low-risk PE should have an agreed plan for monitoring and follow-up.

Other treatments4

  • For people with confirmed PE and haemodynamic instability, offer continuous UFH infusion and consider thrombolytic therapy.

  • Inferior vena caval filters should be offered to patients with PE:

    • Only as part of a clinical study or when anticoagulation is contra-indicated.

    • When arrangements can be made to remove the filter as soon as clinically appropriate.

Surgical embolectomy has been performed for high-risk PE, and also for selected patients with intermediate- or high-risk PE, particularly if thrombolysis is contra-indicated or has failed. Surgical embolectomy has also been successfully performed in patients with right heart thrombi straddling the interatrial septum through a patent foramen ovale6 .


PE is the leading cause of pregnancy-related maternal death in developed countries. The risk of PE is higher in the postpartum period, particularly after a caesarean section. Pregnancy does not alter the clinical features of PE but, as pregnant women often complain of breathlessness, this symptom should be interpreted with caution.

See the separate Venous Thromboembolism in Pregnancy article.

Complications and prognosis

  • If left untreated, the prognosis for PE is poor. Even when treated, some patients develop chronic thromboembolic pulmonary hypertension, which is caused by obstruction of the pulmonary arteries due to PE. This puts excessive pressure on the heart, which can cause heart failure4 .

  • In the International Cooperative Pulmonary Embolism Registry, the all-cause mortality rate at three months associated with acute PE was 17%. PE was considered to be the cause of death in 45% of patients8 .

  • Important prognostic factors associated with death from PE were age older than 70 years, cancer, congestive heart failure, COPD, systolic arterial hypotension, tachypnoea, and right ventricular hypokinesis on echocardiography8 .

  • The mortality rate is lower in those who are haemodynamically stable and higher in those who present in cardiorespiratory arrest4 .

  • Some patients with dyspnoea or right heart failure have severe pulmonary hypertension due to silent recurrent PE (chronic thromboembolic pulmonary hypertension). This condition is probably a distinct disease entity, different from acute PE.


See the separate Prevention of Venous Thromboembolism article.

Further reading and references

  1. Wu HD, Song ZK, Cao HY, et al; Successful treatment of amniotic fluid embolism complicated by disseminated intravascular coagulation with rivaroxaban: A case report. Medicine (Baltimore). 2020 Jan;99(4):e18951. doi: 10.1097/MD.0000000000018951.
  2. Rivaroxaban for treating pulmonary embolism and preventing recurrent venous thromboembolism; NICE Technology Appraisal Guidance, June 2013
  3. 2014 ESC Guidelines on the diagnosis and management of acute pulmonary embolism; European Heart Journal
  4. Venous thromboembolic diseases: diagnosis, management and thrombophilia testing; NICE Guidance (March 2020 - last updated August 2023)
  5. PERC Rule for Pulmonary Embolism; MD CALC, 2020
  6. Guidelines for the diagnosis and management of acute pulmonary embolism developed in collaboration with the European Respiratory Society (ERS): The Task Force for the diagnosis and management of acute pulmonary embolism of the European Society of Cardiology, 2019
  7. Ambesh P, Kapoor A, Kumar S, et al; The dilemma of the "ischemic-looking" electrocardiogram: Pulmonary embolism or acute coronary syndrome? Ann Card Anaesth. 2019 Jan-Mar;22(1):89-91. doi: 10.4103/aca.ACA_40_18.
  8. Goldhaber SZ, Bounameaux H; Pulmonary embolism and deep vein thrombosis. Lancet. 2012 May 12;379(9828):1835-46. Epub 2012 Apr 10.
  9. Venous thromboembolism in adults; NICE Quality standard, August 2021

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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