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Educational draft · awaiting clinical reviewUse Rapid for revision, not patient-care decisions. Check current national and local guidance and the BNF or BNFC before acting.

Suspected pulmonary embolism: probability and diagnosis

Respiratory · UK scope · Sources checked 27 Aug 2026 · Clinical review pending

RapidFull
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Escalate

Shock, persistent hypotension, peri-arrest physiology or cardiac arrest with suspected PE is a high-risk PE pathway: resuscitate, obtain immediate senior/critical-care input and assess for reperfusion. Do not send an unstable patient away for routine imaging if bedside evidence and physiology demand emergency treatment.

Synopsis

Move from a non-specific presentation to a defensible pulmonary embolism diagnosis using clinical probability, D-dimer and the right imaging test without delaying treatment in an unstable patient.

  • Think PE with otherwise unexplained acute dyspnoea, pleuritic chest pain, haemoptysis, syncope, tachycardia, hypoxaemia or signs of DVT; none is diagnostic in isolation.
  • First assess physiological stability and plausible alternatives. Obtain chest radiography to look for another cause, but a normal film neither proves nor excludes PE.
  • When overall clinical suspicion is low and another diagnosis is feasible, NICE says the 8-item PERC rule may be considered to decide whether further PE investigation is needed; do not use PERC in moderate or high suspicion.
  • If PE remains suspected, calculate the 2-level PE Wells score: more than 4 is PE likely; 4 or less is PE unlikely.
  • PE likely: arrange CTPA immediately, aiming for the result within 4 hours; give interim therapeutic anticoagulation if imaging cannot be completed within 4 hours and bleeding risk permits.
  • PE unlikely: obtain D-dimer within 4 hours; give interim therapeutic anticoagulation if the result will be delayed beyond 4 hours. A positive result leads to imaging.
  • Consider an age-adjusted D-dimer threshold for people over 50. Use the locally validated assay threshold rather than inventing a universal unit conversion.
  • Use V/Q SPECT, or planar V/Q if SPECT is unavailable, when contrast allergy, severe renal impairment or radiation considerations make CTPA unsuitable and the chest radiograph permits useful interpretation.
  • Obtain FBC, renal and liver function, PT and APTT before anticoagulation when possible, but NICE says not to wait for these results before starting indicated interim anticoagulation.
  • A negative CTPA ends the PE pathway in most patients, but assess for DVT if clinically suspected and actively pursue an alternative diagnosis rather than stopping at 'PE excluded'.

    • Key red flags

    High-risk physiology

    Cardiac arrest, obstructive shock, persistent systolic hypotension, rising lactate, altered consciousness or rapidly escalating oxygen need suggests high-risk PE or another immediately reversible cause.

    Important mimics

    ACS, aortic syndrome, pneumothorax, pneumonia, asthma/COPD, acute heart failure, pericarditis, sepsis and panic symptoms can look similar; assess them in parallel when clinically plausible.

    Investigation priorities

    01
    ABCDE observations and 12-lead ECGFirst step

    Identify instability and competing emergencies before probability scoring.

    Management branches

    Low initial suspicionUse PERC only in the correct population

    The clinician judges overall PE probability low and another diagnosis is feasible.

    1. Confirm the patient is stable and that PE is not moderate/high probability by gestalt.
    2. Consider all 8 PERC items. If every item is negative, further PE testing may be unnecessary under NICE NG158.
    3. If any PERC item is positive—or PERC is not appropriate—move to the 2-level Wells pathway rather than ordering an unstructured D-dimer.

    Key medicines

    Interim therapeutic enoxaparin (example parenteral option)1 mg/kg subcutaneously every 12 hours is a common treatment regimen for symptomatic PE; use actual product strength and adjust/choose an alternative for severe renal impairment.Check bleeding, platelet count, renal function, recent neuraxial procedure and heparin-induced thrombocytopenia history. Exact LMWH selection and renal adjustment must follow the current product information.
    Controlled oxygenTitrate to SpO2 94–98% for most acutely ill adults, or 88–92% if at risk of hypercapnic respiratory failure pending blood gases.Do not give routinely to a patient already within target. Severe hypoxaemia or shock warrants immediate senior airway/critical-care assessment.
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    Sources and review status5 sources · checked 27 Aug 2026 · clinical review pending+
    Sources

    Sources and review status

    National guidance is shown before implementation-dependent detail. Typical adult dose examples remain subject to patient factors, contraindications and the live BNF or specialist protocol. Source check completed 27 Aug 2026; clinical approval remains outstanding.

    • NICE NG158: Venous thromboembolic diseases—recommendationsNational PE probability, D-dimer, imaging and interim-anticoagulation pathway.
    • NICE NG158 visual summaryOfficial two-level Wells and PE diagnostic flowchart.
    • Resuscitation Council UK 2025: Special circumstancesRecognition and emergency assessment of high-risk PE.
    • BTS guideline for oxygen use in healthcare and emergency settingsTarget saturation ranges during acute assessment.
    • Clexane SmPCLicensed enoxaparin treatment regimens and safety information.

    Editorial contact: Doctor’s Passport editorial team. Source-check date is separate from clinical approval. Report a content problem · Content changes

    Authoring stateRapid draftClinical stateAwaiting reviewJurisdictionUnited Kingdom