The diagnostic workup for pulmonary embolism is one of the most confusing clinical pathways for trainees. Not because the individual tools are complicated — each score is straightforward to calculate. The confusion arises because there are multiple overlapping algorithms with different entry points, different thresholds, and different next steps, and nobody clearly explains when to use which one.
Wells PE. Revised Geneva. PERC Rule. YEARS Algorithm. Age-adjusted D-dimer. sPESI. They all exist for good reasons — but using the wrong tool at the wrong point in the pathway leads to missed PEs or unnecessary CTPAs.
This guide maps the pathway clearly, with links to every PE-related calculator on iatroX.
The NICE NG128 Pathway — The UK Standard
For UK practice, NICE NG128 provides the definitive PE diagnostic algorithm. The pathway is:
Step 1 — Clinical suspicion. Pleuritic chest pain, unexplained dyspnoea, tachycardia, hypoxia, risk factors (immobilisation, surgery, malignancy, oestrogen, previous VTE).
Step 2 — Calculate Wells PE score. Wells PE on iatroX. Seven criteria, maximum 12.5 points. Threshold: ≤4 = PE unlikely; >4 = PE likely.
Step 3a — If PE unlikely (Wells ≤4): D-dimer. If D-dimer negative → PE excluded. If D-dimer positive → CTPA.
Step 3b — If PE likely (Wells >4): Proceed directly to CTPA. Do not delay for D-dimer.
This is the pathway you need for the AKT, the UKMLA, and daily UK clinical practice.
Where the Other Tools Fit
PERC Rule — When to Skip D-dimer Entirely
The PERC (Pulmonary Embolism Rule-out Criteria) identifies patients at such low risk that even a D-dimer is unnecessary. If all 8 criteria are met (age <50, HR <100, SpO₂ >94%, no haemoptysis, no oestrogen use, no surgery/trauma in last 4 weeks, no prior PE/DVT, no unilateral leg swelling), PE can be excluded clinically without any investigation.
When to use it: Before calculating Wells, in patients where your clinical gestalt says PE is very unlikely but you want to formalise the decision not to investigate. PERC is a rule-out tool — it tells you when NOT to test.
Important caveat: PERC was validated in US emergency departments with low prevalence populations. It is not formally part of the NICE NG128 pathway. UK trusts vary in whether they endorse its use. Check your local protocol.
YEARS Algorithm — A Streamlined Alternative
The YEARS algorithm simplifies the pathway by combining three clinical criteria (clinical signs of DVT, haemoptysis, PE as the most likely diagnosis) with D-dimer — but uses different D-dimer thresholds depending on how many YEARS criteria are positive.
No YEARS criteria positive → D-dimer threshold of 1000 ng/mL (higher than standard). 1+ YEARS criteria positive → D-dimer threshold of 500 ng/mL (standard).
This reduces the number of CTPAs performed by raising the D-dimer threshold in very low-risk patients while maintaining sensitivity. It is increasingly used in European emergency departments and is validated in large multicentre trials.
When to use it: When your trust protocol endorses YEARS as an alternative to Wells + standard D-dimer. Not yet formally adopted in NICE NG128 but gaining traction.
Age-Adjusted D-dimer
D-dimer normally rises with age. In patients over 50, using the standard 500 ng/mL threshold produces a high false-positive rate — leading to unnecessary CTPAs. Age-adjusted D-dimer uses the threshold: age × 10 ng/mL for patients over 50 (e.g., for a 72-year-old, the threshold is 720 ng/mL).
When to use it: After a Wells score of ≤4 (PE unlikely) in patients over 50, to reduce false-positive D-dimers and avoid unnecessary imaging. Validated in the ADJUST-PE trial and endorsed by multiple European guidelines.
Calculate age-adjusted D-dimer threshold on iatroX.
Revised Geneva Score
An alternative to Wells PE for estimating pre-test probability. Uses objective criteria only (no subjective "alternative diagnosis" element). Useful when you want to avoid the subjectivity in the Wells score.
When to use it: As an alternative to Wells when your trust protocol specifies Geneva, or for academic comparison. The clinical pathway after scoring (D-dimer vs CTPA) is the same.
sPESI — After Diagnosis, Not Before
The simplified Pulmonary Embolism Severity Index is a risk stratification tool used after PE has been diagnosed — it does not help with diagnosis. It determines whether the patient can be managed as an outpatient (score 0) or requires inpatient monitoring (score ≥1).
When to use it: After CTPA confirms PE. Score 0 = low risk, consider outpatient management with DOAC. Score ≥1 = higher risk, consider inpatient monitoring and assess for right heart strain.
The Flowchart
- Clinical suspicion of PE → PERC: all 8 criteria met? → Yes → PE excluded clinically. No investigation needed.
- PERC not met or not used → Wells PE score.
- Wells ≤4 (PE unlikely) → D-dimer (consider age-adjusted threshold if age >50).
- D-dimer negative → PE excluded.
- D-dimer positive → CTPA.
- Wells >4 (PE likely) → CTPA directly.
- CTPA confirms PE → sPESI for risk stratification → determine inpatient vs outpatient management.
All calculators available at iatrox.com/calculators.
Clinical Pearls
The Wells PE "alternative diagnosis less likely" criterion (3 points) is the most subjective element and the most commonly misapplied. If you are uncertain, score conservatively.
D-dimer is physiologically elevated in pregnancy, post-operatively, in active malignancy, and post-partum. A positive D-dimer in these populations does not reliably indicate PE — consider a lower threshold for proceeding directly to imaging.
Never use D-dimer to "rule out" PE when clinical probability is high (Wells >4). D-dimer has insufficient negative predictive value in high-probability patients.