What is Pulmonary Embolism?
Pulmonary embolism (PE) is a potentially life-threatening condition in which a blood clot (thrombus) travels through the bloodstream and lodges in the pulmonary arteries, blocking blood flow to the lungs. Most PEs originate as deep vein thromboses (DVTs) in the legs or pelvis. PE is the third most common cause of cardiovascular death after heart attack and stroke.
The clinical presentation of PE varies widely, from asymptomatic to sudden death. Common symptoms include acute onset of dyspnea (shortness of breath), pleuritic chest pain (worse with breathing), tachycardia (rapid heart rate), hemoptysis (coughing blood), and syncope (fainting). Because these symptoms overlap with many other conditions, clinical decision tools like the Wells score are essential for risk stratification.
Wells Criteria Explained
The Wells criteria were developed by Dr. Philip S. Wells and colleagues, first published in 1998 and subsequently validated in multiple studies. The criteria assign points to seven clinical features that have been shown to be independent predictors of PE:
| Criterion | Points | Clinical Significance |
|---|---|---|
| Clinical signs/symptoms of DVT | 3.0 | Leg swelling (>3 cm compared to other leg), pain, tenderness along deep veins, pitting edema |
| PE is #1 diagnosis or equally likely | 3.0 | Based on clinical judgment; this is the most subjective criterion but one of the most important |
| Heart rate > 100 bpm | 1.5 | Tachycardia reflects cardiovascular stress from reduced pulmonary blood flow |
| Immobilization or recent surgery | 1.5 | Venous stasis from immobility is a major risk factor for VTE (Virchow's triad) |
| Previous DVT/PE | 1.5 | History of venous thromboembolism significantly increases recurrence risk |
| Hemoptysis | 1.0 | Coughing blood suggests pulmonary infarction from the embolism |
| Malignancy | 1.0 | Cancer increases thrombotic risk through multiple mechanisms (procoagulant factors, venous compression, chemotherapy effects) |
Scoring and Interpretation
The Wells score can be interpreted using either a three-tier model or a simplified two-tier model:
Three-Tier Model
| Score | Risk Category | PE Incidence | Action |
|---|---|---|---|
| 0 – 1 | Low probability | 1.3% | D-dimer testing; if negative, PE effectively excluded |
| 2 – 6 | Moderate probability | 16.2% | D-dimer testing; if positive, proceed to CTPA |
| > 6 | High probability | 37.5% | Proceed directly to CTPA (do not rely on D-dimer alone) |
Two-Tier (Simplified) Model
| Score | Classification | Recommended Action |
|---|---|---|
| ≤ 4 | PE Unlikely | Perform D-dimer; if negative, PE is excluded. If positive, proceed to CTPA. |
| > 4 | PE Likely | Proceed directly to CT pulmonary angiography (CTPA). D-dimer is insufficient to rule out PE. |
Clinical Decision Algorithm
D-Dimer Testing
D-dimer is a fibrin degradation product present in the blood after a blood clot is degraded by fibrinolysis. It is a highly sensitive but non-specific test for venous thromboembolism (VTE).
- High sensitivity (~95%): A negative D-dimer effectively rules out PE in low-to-moderate risk patients
- Low specificity (~50%): D-dimer can be elevated in many conditions including infection, inflammation, surgery, trauma, pregnancy, cancer, and advanced age
- Age-adjusted cutoff: For patients over 50, using an age-adjusted cutoff (age × 10 μg/L instead of the standard 500 μg/L) improves specificity without sacrificing sensitivity
- Not useful alone in high-risk patients: A negative D-dimer does NOT reliably exclude PE when the Wells score is > 6 (high probability)
CT Pulmonary Angiography
CT pulmonary angiography (CTPA) is the gold standard imaging modality for diagnosing PE. It provides direct visualization of thrombus within the pulmonary arteries with high sensitivity (83-100%) and specificity (89-97%).
- Rapid acquisition (seconds), widely available in emergency departments
- Can identify alternative diagnoses (pneumonia, aortic dissection, pneumothorax)
- Can assess right heart strain, indicating massive PE
- Limitations: radiation exposure, contrast allergy risk, limited in renal insufficiency, may miss subsegmental PE
- Alternative: V/Q (ventilation-perfusion) scan for patients who cannot receive contrast
Treatment Overview
Treatment of PE depends on the severity and hemodynamic stability of the patient:
| PE Severity | Characteristics | Treatment |
|---|---|---|
| Low-risk (submassive) | Hemodynamically stable, no RV dysfunction | Anticoagulation alone (heparin bridge to warfarin or DOAC) |
| Submassive | Stable but RV dysfunction/elevated troponin | Anticoagulation; consider thrombolysis if deterioration |
| Massive | Hemodynamically unstable (hypotension, shock) | Systemic thrombolysis, catheter-directed therapy, or surgical embolectomy |
DVT and PE Relationship
Deep vein thrombosis (DVT) and pulmonary embolism are two manifestations of the same disease process: venous thromboembolism (VTE). Understanding this relationship is critical:
- Approximately 50% of patients with proximal DVT have asymptomatic PE on imaging
- About 70% of patients diagnosed with PE have identifiable DVT on ultrasound
- The pathophysiology involves Virchow's triad: venous stasis, endothelial injury, and hypercoagulability
- Risk factors for both include surgery, immobilization, cancer, pregnancy, oral contraceptives, obesity, and inherited thrombophilias
- Treatment is the same for both conditions: anticoagulation for at least 3 months
Limitations
- Subjective criterion: "PE is #1 diagnosis or equally likely" (3 points) relies on clinical gestalt and varies between clinicians
- Not validated in all populations: Originally studied in emergency department settings; may not perform identically in outpatient or inpatient settings
- Pregnancy: The Wells score has not been well-validated in pregnant patients, who have physiologically elevated D-dimer levels
- Age: D-dimer specificity decreases with age, potentially leading to more false-positive results and unnecessary CTPA scans
- Cannot replace clinical judgment: The score is a decision aid, not a replacement for thorough clinical evaluation
Frequently Asked Questions
What is the maximum Wells score?
The maximum Wells score for PE is 12.5 points, achieved when all seven criteria are positive. In practice, scores above 6 are uncommon and indicate high clinical probability of PE.
Can the Wells score be used to diagnose PE?
No. The Wells score is a pre-test probability tool that helps determine which diagnostic tests to order. It cannot confirm or exclude PE on its own. Definitive diagnosis requires imaging (CTPA or V/Q scan) or, in low-risk patients, a negative D-dimer test.
Is there a Wells score for DVT as well?
Yes. There is a separate Wells score for DVT that uses a different set of criteria specific to lower extremity deep vein thrombosis. The criteria and point values are different from the PE version.
What if my patient has a low Wells score but I still suspect PE?
Clinical judgment should always take precedence. If you have a strong clinical suspicion despite a low Wells score, it is appropriate to pursue further workup. The Wells score is an aid, not a rigid protocol. Document your clinical reasoning for proceeding with testing.
How does the Wells score compare to the Geneva score?
The revised Geneva score is an alternative clinical decision rule for PE that uses only objective criteria (no subjective "PE is likely" criterion). Both scores have similar diagnostic accuracy. The Geneva score may be preferred in settings where inter-rater reliability is a concern, while the Wells score is more widely used and validated.