Wells' Criteria for Pulmonary Embolism (PE) is a widely used clinical prediction rule that helps estimate the probability of pulmonary embolism in patients presenting with symptoms such as dyspnea, chest pain, or unexplained tachycardia. Developed by Dr. Philip Wells and colleagues in the 1990s, the score is designed to guide decision-making about diagnostic testing, particularly whether a D-dimer test or imaging studies (such as CT pulmonary angiography) are warranted.
Pulmonary embolism is a potentially life-threatening condition caused by obstruction of pulmonary arteries by thrombi, most often originating from deep veins of the legs. Accurate and timely diagnosis is critical. However, because the symptoms of PE overlap with other conditions, Wells' Criteria provides an evidence-based framework to estimate pre-test probability and optimize resource use.
Scoring Components
Wells' Criteria consists of several clinical variables, each assigned a point value. The original and simplified versions are both used in practice.
| Clinical Feature | Points |
|---|---|
| Clinical signs and symptoms of deep vein thrombosis (DVT) | 3.0 |
| An alternative diagnosis is less likely than PE | 3.0 |
| Heart rate > 100 beats/min | 1.5 |
| Immobilization > 3 days or surgery in the previous 4 weeks | 1.5 |
| Previous DVT or PE | 1.5 |
| Hemoptysis | 1.0 |
| Malignancy (treated within 6 months or palliative care) | 1.0 |
Interpretation
The Wells' score can be interpreted in two ways: the original three-tier model or the simplified two-tier model.
Three-Tier Model
- > 6 points: High probability of PE (≈ 60% risk)
- 2–6 points: Moderate probability of PE (≈ 20–30% risk)
- < 2 points: Low probability of PE (≈ 5% risk)
Two-Tier Model (Simplified)
- > 4 points: PE likely
- ≤ 4 points: PE unlikely
These probability categories are used in conjunction with D-dimer testing. For patients with “PE unlikely” and a negative D-dimer, PE can be safely excluded without imaging.
Clinical Significance
Wells' Criteria has become a cornerstone of PE diagnosis due to its simplicity and effectiveness:
- Reduces unnecessary imaging: By stratifying patients, many avoid unnecessary CT scans, lowering radiation exposure and healthcare costs.
- Facilitates rapid triage: Helps emergency physicians prioritize patients for immediate imaging or anticoagulation.
- Improves patient safety: Early identification of high-risk patients reduces morbidity and mortality from untreated PE.
- Guides use of D-dimer: Ensures that D-dimer testing is applied in the correct patient populations.
The combination of Wells' score, D-dimer testing, and imaging forms the backbone of modern diagnostic algorithms for PE.
Indications for Use
Wells' Criteria should be applied in:
- Patients presenting with unexplained shortness of breath, pleuritic chest pain, or tachycardia.
- Patients with risk factors for venous thromboembolism, such as immobilization, recent surgery, or malignancy.
- Emergency department or inpatient settings where rapid evaluation of PE risk is required.
- Clinical decision-making about ordering D-dimer assays and CT pulmonary angiography.
Limitations
Although highly useful, Wells' Criteria is not perfect and should not be used in isolation:
- Subjective components: The criterion “alternative diagnosis less likely than PE” can vary between clinicians, introducing bias.
- Variable predictive values: Performance may differ in diverse populations and care settings.
- Not a standalone diagnostic tool: Must be used alongside D-dimer testing and imaging for definitive diagnosis.
- May underestimate risk: In certain subgroups, such as pregnant women or postoperative patients, PE may still occur despite low scores.