What is the Wells Score?
The Wells score is a validated clinical prediction rule that assigns points to seven clinical variables to stratify patients with suspected pulmonary embolism into probability categories (low, intermediate, or high risk), guiding decisions about D-dimer testing and imaging. 1, 2
Components and Point Values
The Wells score consists of seven variables, each assigned specific point values 1, 3:
- Clinical signs/symptoms of deep vein thrombosis (leg swelling and pain on palpation): 3 points 1, 3
- Pulmonary embolism is the number one diagnosis or equally likely as an alternative diagnosis: 3 points 3
- Heart rate greater than 100 bpm (tachycardia): 1.5 points 3
- Immobilization for ≥3 days or surgery in the previous 4 weeks: 1.5 points 3
- Previous deep vein thrombosis or pulmonary embolism: 1.5 points 3
- Hemoptysis: 1 point 3
- Active malignancy (treatment within 6 months or palliative): 1 point 3
Risk Stratification Categories
The Wells score categorizes patients into three probability groups 1, 2:
- Low probability (0-1 points): 3.6% PE prevalence 1, 2
- Intermediate/moderate probability (2-6 points): 20.5% PE prevalence 1, 2
- High probability (>6 points): 66.7% PE prevalence 1, 2
Alternative Dichotomous Interpretation
The Wells score can also be dichotomized into two categories 1, 4:
Clinical Application Algorithm
For low or intermediate probability patients (Wells score ≤6), obtain high-sensitivity D-dimer testing; if negative, PE is safely excluded without imaging 3. When combined with a negative D-dimer, the negative predictive value is 99.5% 2, 3.
For high probability patients (Wells score >6), proceed directly to CT pulmonary angiography without D-dimer testing, as a negative D-dimer will not obviate the need for imaging 1, 3. In these patients, initiate anticoagulation immediately while awaiting imaging 3.
Diagnostic Performance
The Wells score demonstrates superior discriminative ability compared to the Geneva score, with an area under the ROC curve of 0.75-0.85 versus 0.54-0.76 1, 5. The Wells score identifies approximately 73% of patients as low risk, with a PE rate of only 3.0% in this group 1.
The Wells score shows moderate to substantial interrater agreement, with kappa values of 0.54 for trichotomized scoring and 0.72 for dichotomized scoring 4.
Simplified Version
A simplified Wells score assigns only 1 point to each of the seven variables (rather than the weighted scoring above), which has been validated and shows similar safety and clinical utility 6, 7. The simplified version uses a cut-off of ≤1 point for "PE unlikely" and maintains a three-month VTE incidence of 0.5% when combined with normal D-dimer 6, 7.
Critical Pitfalls
Do not use D-dimer testing in high-probability patients (Wells score >6), as it has low negative predictive value in this population and will not change management 1. Do not apply the Wells score in isolation—it must be combined with D-dimer testing (for low/intermediate probability) or imaging (for high probability) to safely exclude or diagnose PE 2, 3.