Suspected pulmonary embolism (adult)
Adults, including pregnancy and up to 6 weeks post-partum. Not for children.
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Pulmonary Embolism Imaging Protocol Selection
Pulmonary Embolism Imaging Protocol Selection: Suspected pulmonary embolism (adult) → Haemodynamically unstable? → Unstable: suspected high-risk PE → Un...
Pathway Overview
18 steps
Algorithm Steps
18 total
01Start 02Decision Haemodynamically unstable?
Cardiac arrest; or SBP <90 mmHg (or vasopressors needed) with end-organ hypoperfusion; or SBP <90 mmHg or a fall of 40 mmHg or more for >15 min, not due to arrhythmia, hypovolaemia or sepsis.
- If Yes
03Warning Unstable: suspected high-risk PE
Do not use scores or D-dimer. Start IV unfractionated heparin with a weight-adjusted bolus now, unless contraindicated (e.g. active bleeding).
- Bedside echo now: RV dysfunction?
- CTPA only if immediately available and the patient is safe to move
- Too unstable for CTPA and RV dysfunction on echo: treat as high-risk PE
04End Unstable: confirm high-risk PE or find other cause
CTPA positive, or RV dysfunction when CTPA is not feasible: treat as high-risk PE (emergency reperfusion; senior team). No RV dysfunction or CTPA negative: look for other causes of shock. Once stabilised, confirm with CTPA.
If No05Action Stable adult: assess clinical probability
Use a validated rule: Wells, revised Geneva, or YEARS items (DVT signs, haemoptysis, PE most likely diagnosis).
- ED, low clinical probability and all 8 PERC criteria met: further testing may not be needed (evidence from low-prevalence settings; not for pregnancy)
- Pregnant or up to 6 weeks post-partum: use the pregnancy-adapted YEARS algorithm. DVT signs: leg ultrasound (CUS) first; proximal DVT confirms VTE
06Decision High clinical probability (or PE likely)?
High probability: go straight to anticoagulation and imaging. Do not test D-dimer; a normal result does not exclude PE.
- If Yes
07Action PE not excluded: image; anticoagulate if high or intermediate probability
High or intermediate probability: start anticoagulation without delay unless contraindicated (e.g. active bleeding). Low probability with positive D-dimer: anticoagulate if imaging will be delayed. Pregnancy with high probability or positive D-dimer: start therapeutic LMWH now, unless contraindicated. Do not delay imaging.
- Pregnancy: therapeutic LMWH only; do not use DOACs
- CrCl 30 mL/min or less: IV UFH preferred; no DOAC. LMWH only if CrCl 15-30 mL/min, with an adjusted dose
- Breastfeeding or antiphospholipid syndrome: no DOAC; use LMWH or UFH
- Leg symptoms: proximal DVT on leg ultrasound (CUS) confirms VTE; CTPA can be avoided
08Decision Pregnant or up to 6 weeks post-partum?
- If Yes
09Decision Pregnancy: proximal DVT on leg ultrasound (CUS)?
Do CUS if there are DVT symptoms or signs. No leg symptoms: answer No. CUS can miss pelvic vein DVT: whole-leg swelling or buttock pain, consider MR venography.
- If Yes
10End Pregnancy, proximal DVT: treat as PE
Continue therapeutic LMWH. No chest imaging needed. Assess PE severity. Refer to a multidisciplinary team experienced in PE in pregnancy.
If No11Decision Pregnancy: chest X-ray normal?
- If Yes
- Yes, normal
12End Pregnancy, normal chest X-ray: low-dose CTPA or perfusion scan
Choose by local expertise (2026 AHA/ACC favours low-dose CTPA). Use a low-radiation protocol. Previous contrast anaphylaxis, or AKI or eGFR <30 mL/min/1.73 m2 (not on dialysis): use a perfusion scan. Negative: PE excluded. Positive or indeterminate: review by a radiologist or nuclear medicine physician experienced in pregnancy. Confirmed PE: continue therapeutic LMWH, assess severity, and refer to a multidisciplinary team experienced in PE in pregnancy.
If No- No, abnormal
13End Pregnancy, abnormal chest X-ray: low-dose CTPA
Previous contrast anaphylaxis, or AKI or eGFR <30 mL/min/1.73 m2 (not on dialysis): discuss with radiology (perfusion scan, or CTPA with local contrast precautions); keep LMWH going. Negative: PE excluded. Positive or indeterminate: review by a radiologist experienced in PE in pregnancy. Confirmed PE: continue therapeutic LMWH, assess severity, and refer to a multidisciplinary team experienced in PE in pregnancy.
If No14Decision Not pregnant: contrast contraindicated?
Previous anaphylaxis to iodinated contrast, or AKI or eGFR <30 mL/min/1.73 m2 (not on dialysis).
- If Yes
15End Contrast anaphylaxis or severe renal impairment: V/Q scan
Use V/Q SPECT if available. Normal perfusion: PE excluded. High-probability scan: PE confirmed. Non-diagnostic scan: add proximal leg CUS; a negative CUS excludes PE only if clinical probability is low. Otherwise seek senior and radiology advice. V/Q not available promptly: continue anticoagulation and discuss with radiology; CTPA with local contrast precautions may still be needed. PE confirmed: continue anticoagulation; assess severity (sPESI, RV size on CT or echo, troponin). PE excluded: stop anticoagulation started for suspected PE, unless there is another indication; look for another diagnosis.
If No16End No contrast contraindication: CTPA
Segmental or more proximal filling defect: PE confirmed. Normal CTPA: PE excluded (high probability: consider further tests if doubt remains). Isolated subsegmental defect: consider further imaging. V/Q is an alternative in young women with a normal chest X-ray. PE confirmed: continue anticoagulation; assess severity (sPESI, RV size on CT or echo, troponin). PE excluded: stop anticoagulation started for suspected PE, unless there is another indication; look for another diagnosis.
If No17Decision Low or intermediate probability: D-dimer negative?
Use a highly sensitive assay. Negative: below 500 µg/L FEU (0.5 mg/L). Age over 50 years: below age x 10 µg/L FEU. YEARS: no items and below 1000 µg/L, or 1 or more items and below 500 µg/L. Positive: go to the step 'PE not excluded: image; anticoagulate if high or intermediate probability'.
- If Yes
- Yes, negative
18End Low or intermediate probability, D-dimer negative: PE excluded
No imaging needed. Not valid if clinical probability is high or the patient already takes an anticoagulant. Look for another diagnosis.
If No- No, positive
- Path rejoins step 07Shared downstream outcome
Guideline Source
ACR Appropriateness Criteria: Suspected Pulmonary Embolism (2022 update)
Clinical Safety Information
Clinical Decision Support — Not a Substitute for Clinical Judgment
Individual patient factors may require deviation from these recommendations.
Known Limitations
- Adults only. Clinical probability scores and D-dimer cut-offs are not validated in children.
- D-dimer cut-offs depend on the assay and its units; use the local laboratory cut-off.
- CTPA sensitivity is lower for subsegmental PE.
- V/Q is often non-diagnostic with an abnormal chest X-ray or lung disease.
Contraindicated Populations
Children and adolescents under 18 years
Applicable Regions
USAUUKEU
AU: Australian labs report D-dimer in mg/L FEU or µg/L FEU (0.5 mg/L = 500 µg/L). V/Q availability out of hours varies by site.
EU: ESC 2019 acute PE guideline: age-adjusted and YEARS D-dimer cut-offs accepted.
US: 2026 AHA/ACC/ACCP/ACEP/CHEST multisociety acute PE guideline (doi 10.1016/j.jacc.2025.11.005) and ACR 2022 (Suspected PE). CTPA preferred; V/Q SPECT if CTPA not possible; low-dose CTPA favoured in pregnancy with a normal chest X-ray. Empirical anticoagulation while imaging is awaited: mainly high probability with low bleeding risk.
Version 2Next review: 2027-09-30
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Frequently Asked Questions
What is the Pulmonary Embolism Imaging Protocol Selection?
The Pulmonary Embolism Imaging Protocol Selection is a diagnostic clinical algorithm for Radiology. It provides a structured decision tree to guide clinical decision-making, based on ACR Appropriateness Criteria: Suspected Pulmonary Embolism (2022 update).
What guideline is the Pulmonary Embolism Imaging Protocol Selection based on?
This algorithm is based on ACR Appropriateness Criteria: Suspected Pulmonary Embolism (2022 update) (DOI: 10.1016/j.jacr.2022.09.014).
What are the limitations of the Pulmonary Embolism Imaging Protocol Selection?
Known limitations include: Adults only. Clinical probability scores and D-dimer cut-offs are not validated in children.; D-dimer cut-offs depend on the assay and its units; use the local laboratory cut-off.; CTPA sensitivity is lower for subsegmental PE.; V/Q is often non-diagnostic with an abnormal chest X-ray or lung disease.. Individual patient factors may require deviation from these recommendations.
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