What is the Wells score for pulmonary embolism and how is it calculated and interpreted?

Wells Score for Pulmonary Embolism

What is the Wells Score?

The Wells score is a validated clinical prediction rule that stratifies patients with suspected pulmonary embolism into probability categories to guide D-dimer testing and imaging decisions, with scores interpreted either as a three-tier system (low/intermediate/high risk) or a simplified two-tier system (PE unlikely/PE likely). 1

Components and Point Values

The Wells score consists of 7 clinical variables, each assigned specific point values 2:

• Clinical signs of deep vein thrombosis (leg swelling and pain on palpation): 3 points 2
• PE as likely as or more likely than alternative diagnosis: 3 points 1
• Heart rate >100 beats/min (tachycardia): 1.5 points 1
• Immobilization ≥3 days or surgery in previous 4 weeks: 1.5 points 1
• Previous PE or DVT: 1.5 points 1
• Hemoptysis: 1 point 1
• Active malignancy (treatment within 6 months or palliative): 1 point 1

Interpretation Systems

Three-Tier Interpretation (Traditional)

Low risk (Wells score <2): PE prevalence 3.0-3.6% 1, 3

Intermediate risk (Wells score 2-6): PE prevalence 13-20.5% 1, 3

High risk (Wells score >6): PE prevalence 36-66.7% 1, 3

Two-Tier Interpretation (Simplified/Dichotomized)

PE unlikely (Wells score 0-4): PE prevalence 3-7.8% 1, 2, 3

PE likely (Wells score >4): PE prevalence 28-40.7% 1, 2, 3

Clinical Application Algorithm

For Low-Risk Patients (Wells <2 or "PE Unlikely" with score 0-4):

• First, apply PERC criteria if clinical suspicion is truly low (<15% pretest probability) 2
• If all 8 PERC criteria are met, no further testing is needed 2
• If PERC criteria are not met, obtain high-sensitivity D-dimer 2
• If D-dimer is negative (using age-adjusted cutoff: age × 10 ng/mL for patients >50 years), PE is excluded 2, 4
• If D-dimer is positive, proceed to CTPA 2

For Intermediate-Risk Patients (Wells 2-6):

• Obtain high-sensitivity D-dimer with age-adjusted cutoffs 2, 4
• If negative, PE is excluded 2
• If positive, proceed to CTPA 2

For High-Risk Patients (Wells >6 or "PE Likely" with score >4):

• Proceed directly to CTPA without D-dimer testing, as a negative D-dimer cannot safely exclude PE in this population 2, 1
• In hemodynamically unstable patients, perform bedside echocardiography if CTPA is not immediately available 2

Performance Characteristics

The Wells score demonstrates superior discriminative ability compared to the Geneva score, with an area under the ROC curve of 0.73-0.75 2, 5. When combined with age-adjusted D-dimer testing, the Wells rule achieves an efficiency of 30% (proportion of patients in whom PE can be excluded) with a failure rate of 0.8-0.9% (3-month venous thromboembolism rate) 1, 4.

Simplified Wells Score

A simplified version assigns 1 point to each variable (except the subjective "alternative diagnosis" criterion remains 3 points), making it easier to use in clinical practice 4. The simplified Wells rule combined with age-adjusted D-dimer testing has comparable performance to the original Wells score, with similar efficiency (30%) and failure rates (0.8%) 4.

Critical Limitations and Pitfalls

Interrater Reliability Issues

Moderate interrater agreement exists for several Wells components, including DVT symptoms (κ=0.54), immobilization (κ=0.41), and the subjective "PE more likely than alternative diagnosis" criterion (κ=0.5) 1. The dichotomized Wells score shows only moderate agreement (κ=0.47-0.72) between providers 1, 3.

The Subjective Component Problem

A major criticism is that the Wells score contains the subjective variable "alternative diagnosis less likely than PE," worth 3 points, which essentially represents physician judgment override of the objective components 1. This variable alone can move a patient from low-risk to intermediate-risk category 1.

Population-Specific Limitations

The Wells score may not perform reliably in DVT patients suspected of having coexisting PE, as one study found no association between Wells PE score and occurrence of PE in this specific subgroup 6. Caution against overreliance on Wells criteria as the sole decision-making tool is warranted in this population 6.

D-dimer Limitations in Hospitalized Patients

D-dimer has extremely limited utility in hospitalized patients due to frequent elevation from comorbid conditions, recent surgery, infection, cancer, and inflammation—fewer than 10% of hospitalized patients will have a negative D-dimer 2. In these patients, proceed directly to imaging rather than relying on D-dimer testing 2.

Comparison with Clinical Gestalt

Gestalt clinical assessment performs comparably to the Wells score when used by experienced clinicians, with both methods achieving similar PE rates in low-risk groups (2.6% for gestalt vs 3.0% for Wells) 1. However, formal prediction rules like Wells improve diagnostic safety and reproducibility, particularly for less experienced clinicians 1.