Wells' Criteria for PE
Clinical prediction rule for pulmonary embolism probability
Calculator
Why use it
Guides evidence-based diagnostic strategy for suspected PE. Avoids unnecessary CTPA in low-risk patients. Combined with D-dimer, can safely exclude PE without imaging in low-risk patients.
About
The Wells score for pulmonary embolism stratifies patients into risk categories to guide diagnostic workup. It uses clinical criteria to estimate pre-test probability of PE, determining whether D-dimer testing or CT pulmonary angiography (CTPA) is the appropriate next step.
When to use
- Clinical suspicion of pulmonary embolism
- Acute dyspnea or chest pain workup
- Risk stratification before ordering CTPA
- Decision on D-dimer utility
Formula
Pearls & pitfalls
- Most commonly used as dichotomized: PE unlikely (≤ 4) vs PE likely (> 4).
- D-dimer is only useful in low-probability patients — not recommended if Wells > 4.
- The "alternative diagnosis less likely" criterion is subjective but the most heavily weighted (+3).
- Modified Wells (simplified) gives +1 per criterion instead of the original weighting.
- PERC rule can be applied if Wells ≤ 4 to potentially avoid D-dimer testing.
- Remember: Wells is a pre-test probability tool, not a diagnostic test.
Next steps
Score ≤ 4: D-dimer; if negative, PE excluded. Score > 4: Proceed directly to CTPA. If CTPA positive, initiate anticoagulation. Consider PERC rule for very low-risk patients.
Evidence
Validated in the Christopher Study (JAMA 2006): Wells + D-dimer safely excluded PE with 3-month VTE rate < 1%. The YEARS algorithm (Lancet 2017) provides an alternative approach.
References
- Wells PS et al. Derivation of a simple clinical model to categorize patients probability of pulmonary embolism. Thromb Haemost. 2000;83(3):416-420. — link
- van Belle A et al. Effectiveness of managing suspected pulmonary embolism using an algorithm combining clinical probability, D-dimer testing, and computed tomography. JAMA. 2006;295(2):172-179. — link