Wells Score for Pulmonary Embolism
The Wells score is a validated clinical prediction rule that stratifies patients with suspected PE into risk categories to guide D-dimer testing and imaging decisions, with low-risk patients (score ≤4) safely managed with D-dimer testing alone, while high-risk patients (score >4) require direct imaging with CT pulmonary angiography. 1, 2
Components and Scoring System
The Wells score consists of 7 clinical variables, each assigned specific point values 3:
- Clinical signs of DVT (leg swelling, pain on palpation): 3 points
- PE as likely or more likely than alternative diagnosis: 3 points
- Heart rate >100 bpm: 1.5 points
- Immobilization ≥3 days or surgery within 4 weeks: 1.5 points
- Previous PE or DVT: 1.5 points
- Hemoptysis: 1 point
- Active malignancy: 1 point
A simplified version assigns 1 point to each variable, which has been validated with similar diagnostic performance 4.
Risk Stratification and PE Probability
The Wells score categorizes patients into three probability groups 3, 5:
- Low risk (0-1 points): 3.6% PE probability
- Intermediate risk (2-6 points): 20.5% PE probability
- High risk (>6 points): 66.7% PE probability
An alternative dichotomous interpretation classifies patients as 3, 1:
- PE unlikely (0-4 points): 7.8% PE probability
- PE likely (>4 points): 40.7% PE probability
Clinical Application Algorithm
For Low-Risk Patients (Score ≤4)
Apply PERC criteria first if clinical probability is very low 2. All 8 PERC criteria must be met (age <50, pulse <100, SaO₂ >94%, no hemoptysis, no estrogen use, no prior VTE, no unilateral leg swelling, no surgery/trauma within 4 weeks) to exclude PE without further testing 2.
If PERC criteria not met, obtain high-sensitivity D-dimer 2. A negative D-dimer (<500 ng/mL, or age-adjusted cutoff of age × 10 ng/mL for patients >50 years) safely excludes PE with a failure rate of 1.5% 3, 2, 6.
For Intermediate-Risk Patients (Score 2-6)
Obtain D-dimer testing 2. If negative, PE is excluded 1. If positive, proceed to CT pulmonary angiography 2.
For High-Risk Patients (Score >6)
Proceed directly to CT pulmonary angiography without D-dimer testing, as a negative D-dimer will not obviate the need for imaging 2. In hemodynamically unstable patients, initiate IV unfractionated heparin immediately and perform bedside echocardiography if CTPA unavailable 2.
Comparative 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 3, 5. The Wells score identified 73% of patients as low risk with a PE rate of 3.0% in this group 3.
When compared to clinical gestalt, the Wells rule shows similar discriminative ability (c statistic 0.80 vs 0.77) but superior efficiency, allowing PE exclusion in 45% of patients versus 25% with gestalt alone 6.
Critical Pitfalls and Limitations
The subjective component "PE as likely as alternative diagnosis" introduces interobserver variability 7, 6. This element requires clinical judgment and may reduce reproducibility between providers.
The Wells score may perform poorly in specific subpopulations, particularly DVT patients with suspected coexisting PE, where it failed to predict PE occurrence 8. In these patients, tachycardia and hemoptysis were the only predictive variables 8.
D-dimer has extremely limited utility in hospitalized patients due to frequent elevation from comorbid conditions, surgery, infection, and inflammation—fewer than 10% of hospitalized patients have negative D-dimer 2. In these patients, proceed directly to imaging based on clinical probability.
Age-adjusted D-dimer cutoffs should be used in patients >50 years (age × 10 ng/mL) rather than the standard 500 ng/mL threshold, which increases the proportion of patients in whom PE can be excluded from 6.4% to 30% without additional false-negative findings 2.
Efficiency and Safety
Combining the Wells score with D-dimer testing safely reduces the need for CT pulmonary angiography in approximately 30% of patients with suspected PE 1. The failure rate when using Wells score ≤4 plus negative D-dimer is 1.5% (95% CI 0.4%-3.7%), which is considered acceptably safe for clinical practice 6.