How is the Well's score (Wells' score for pulmonary embolism) calculated?

Calculating the Wells Score for Pulmonary Embolism

The Wells score for pulmonary embolism consists of 7 clinical variables that classify patients into risk categories to determine the likelihood of PE and guide further diagnostic testing. 1

Wells Score Components and Point Values

Each of the following criteria contributes points to the total Wells score:

• Clinical signs and symptoms of DVT (swelling, pain with palpation): 3 points 1, 2
• Alternative diagnosis less likely than PE: 3 points 1
• Heart rate > 100 beats/min: 1.5 points 1
• Immobilization (≥3 days) or surgery in previous 4 weeks: 1.5 points 1
• Previous DVT/PE: 1.5 points 1
• Hemoptysis: 1 point 1
• Malignancy (treatment ongoing, treated in the last 6 months, or palliative): 1 point 1

Risk Stratification

The total score is used to classify patients into risk categories:

Traditional Three-Tier Interpretation:

• Low risk: 0-1 points (PE prevalence ~3.6%) 1
• Moderate risk: 2-6 points (PE prevalence ~20.5%) 1
• High risk: >6 points (PE prevalence ~66.7%) 1

Alternative Two-Tier Interpretation:

• PE unlikely: 0-4 points (PE prevalence ~7.8%) 1
• PE likely: >4 points (PE prevalence ~40.7%) 1

Clinical Application

• For patients with low probability/PE unlikely classification and negative D-dimer, further imaging can be safely avoided 1, 2
• For patients with moderate to high probability or positive D-dimer, CT pulmonary angiography is typically recommended 1
• The Wells score has moderate to substantial interrater agreement (kappa values of 0.54 for the three-tier system and 0.72 for the two-tier system) 3

Performance Characteristics

• When combined with D-dimer testing, the Wells score can safely reduce the need for CT pulmonary angiography in approximately 30% of patients with suspected PE 2, 4
• The Wells score has a sensitivity of 69.6% and specificity of 88.2% when combined with point-of-care ultrasound 4
• In validation studies, the Wells score performed better than other scoring systems like the simplified revised Geneva score, with an area under the ROC curve of 0.85 compared to 0.76 5

Important Considerations

• The "alternative diagnosis less likely than PE" criterion is somewhat subjective and may affect interobserver reliability 4
• The Wells score may have limitations in specific populations, such as COVID-19 patients, where only 33% of patients with confirmed PE had a Wells score ≥4 6
• While originally validated in emergency department settings, the Wells score has also shown reliability in trauma patients 7

Pitfalls to Avoid

• Do not rely solely on the Wells score without considering D-dimer testing in low-risk patients 1, 2
• Avoid overestimating the "alternative diagnosis less likely than PE" criterion, as this can artificially lower the score 1
• Remember that a negative Wells score (low probability) combined with a negative D-dimer has a high negative predictive value, but does not completely exclude PE in all cases 2, 3