Pulmonary Embolism (PE) is a potentially life-threatening condition caused by blood clots in the pulmonary arteries. The Wells Score for PE is a validated clinical prediction rule designed to assist clinicians in estimating the pre-test probability of a PE in symptomatic patients. This probability guides the appropriate use of further diagnostic modalities, such as D-dimer testing and computed tomography pulmonary angiography (CTPA).
Clinical Criteria and Scoring
The score evaluates seven key clinical features and historical factors:
- Clinical signs and symptoms of DVT: Objective leg swelling and pain with palpation in the deep vein system (+3.0 points)
- Alternative diagnosis is less likely than PE: Based on clinical judgment (+3.0 points)
- Heart rate > 100 beats per minute (+1.5 points)
- Immobilization for ≥ 3 days or surgery in the previous 4 weeks (+1.5 points)
- Previous, objectively diagnosed PE or DVT (+1.5 points)
- Hemoptysis (+1.0 point)
- Malignancy: On treatment, treated in the last 6 months, or receiving palliative care (+1.0 point)
Interpretation Models
The score interpretation typically employs either a traditional three-tier model or a simplified two-tier model. The two-tier model is widely recommended in current algorithms as it pairs seamlessly with D-dimer testing pathways.
Two-Tier Model (PE Likely / Unlikely)
This model creates a dichotomous clinical decision pathway:
- Score > 4 (PE Likely): The pre-test probability is high enough that D-dimer testing is not recommended. Diagnostic imaging (e.g., CTPA) should be performed directly.
- Score ≤ 4 (PE Unlikely): The pre-test probability is lower. Clinicians can proceed with a moderate or high-sensitivity D-dimer test (or employ the PERC rule). If the D-dimer is negative, PE is ruled out. If positive, imaging is required.
Three-Tier Model (High / Moderate / Low)
The original classification system stratifies patients into three probability groups:
- Score > 6 (High Risk): Probability of PE is approximately 59%.
- Score 2.0 - 6.0 (Moderate Risk): Probability of PE is approximately 16%.
- Score < 2.0 (Low Risk): Probability of PE is approximately 1.3%.
Clinical Considerations & Limitations
Like all clinical decision tools, the Wells Score for PE is not definitive. It relies heavily on the clinician's subjective assessment of the criteria "Alternative diagnosis is less likely than PE." If a patient clearly presents with symptoms of an alternative pathology (e.g., pneumonia with a clear consolidation on an X-ray), the score decreases significantly.
This score is intended only for patients in whom there is already a clinical suspicion of PE. Applying it to unselected patient populations leads to over-testing.
Clinical Examples
Scenario 1: High Probability
A 65-year-old female presents with sudden onset shortness of breath and pleuritic chest pain. She has a history of breast cancer currently undergoing chemotherapy. Her heart rate is 115 bpm. On exam, her left leg is swollen and tender.
Score Calculation:
- Clinical signs of DVT (+3.0)
- Alternative diagnosis less likely (+3.0)
- Heart rate > 100 bpm (+1.5)
- Active malignancy (+1.0)
Total Score: 8.5 (PE Likely / High Risk)
Action: Proceed directly to diagnostic imaging (CTPA) without D-dimer testing.
Scenario 2: Low Probability
A 32-year-old healthy male presents with mild chest pain after a coughing fit. He has no recent surgeries, no prolonged immobilization, and no history of clots. Heart rate is 88 bpm. Leg exam is normal. You suspect costochondritis or a mild viral illness.
Score Calculation:
- Alternative diagnosis is MORE likely than PE (0 points)
- All other criteria are negative (0 points)
Total Score: 0 (PE Unlikely / Low Risk)
Action: Consider PERC rule out. If PERC positive, perform a D-dimer test.
References
- Wells, P. S., Anderson, D. R., Rodger, M., et al. (2000). Derivation of a simple clinical model to categorize patients probability of pulmonary embolism: increasing the models utility with the SimpliRED D-dimer. Thrombosis and Haemostasis, 83(3), 416-420.
- Wells, P. S., Anderson, D. R., Rodger, M., et al. (2001). Excluding pulmonary embolism at the bedside without diagnostic imaging: management of patients with suspected pulmonary embolism presenting to the emergency department by using a simple clinical model and d-dimer. Annals of Internal Medicine, 135(2), 98-107.