What is the Wells Score?
The Wells Score is a clinical prediction rule that estimates how likely a patient's presentation is to represent a pulmonary embolism, based on history and examination findings alone — before any blood test or imaging. It was developed by Philip Wells and colleagues in the late 1990s and has been validated in multiple subsequent studies, including the Christopher study, which confirmed that combining a low Wells Score with a negative D-dimer safely rules out PE without imaging in most patients.
How to calculate the Wells Score
Seven criteria are scored, each adding points toward the total:
- Clinical signs/symptoms of DVT — +3.0
- PE is the #1 diagnosis, or equally likely — +3.0
- Heart rate >100/min — +1.5
- Immobilization ≥3 days, or surgery in the past 4 weeks — +1.5
- Previous, objectively diagnosed DVT or PE — +1.5
- Hemoptysis — +1.0
- Malignancy treated within 6 months, or palliative — +1.0
Interpretation
| Score | Probability | Suggested next step |
|---|---|---|
| ≤4 | PE unlikely | D-dimer testing to further rule out PE |
| >4 | PE likely | Proceed to imaging (CT pulmonary angiography) |
This is the simplified two-tier model. A three-tier version (low / moderate / high probability, using cutoffs of roughly 0–1, 2–6, and ≥7) is also used in some settings, particularly outside North America.
Wells Score vs. other PE tools
For patients who score very low risk on Wells, the PERC rule (Pulmonary Embolism Rule-out Criteria) can sometimes avoid D-dimer testing altogether in low-probability patients. The Geneva Score is a comparable alternative prediction rule used in some institutions, with similar performance to Wells.
Limitations
The Wells Score relies partly on clinical gestalt ("PE is #1 diagnosis, or equally likely"), which introduces some inter-observer variability. It should be used as decision support alongside — not instead of — careful clinical assessment, and local protocols may specify a preferred PE risk tool.
References
Wells PS, Anderson DR, Rodger M, et al. Derivation of a simple clinical model to categorize patients' probability of pulmonary embolism. Thromb Haemost. 2000. van Belle A, Büller HR, Huisman MV, et al. (Christopher Study Investigators). Effectiveness of managing suspected pulmonary embolism using an algorithm combining clinical probability, D-dimer testing, and CT. JAMA. 2006.