Wells Criteria - Derivation of a simple clinical model to categorize patientsŐ probability of pulmonary embolism. 

Rules
1. IF [Wells score >4] THEN [CTPE]
2. IF [Wells Score <=4] AND [D-dimer normal] THEN NOT [CTPE]
3. IF [Wells score <=4] AND [D-Dimer elevated] THEN [CTPE]

Additional Values (Wells score)
- Clinical signs and symptoms of DVT (minimum leg swelling and pain with palpation of the deep veins) (3 points)
- An alternative diagnosis is less likely than PE (3 points)
- Heart rate >100 (1.5 points)
- Immobilization or surgery in the previous 4 weeks (1.5 points)
- Previous DVT/PE (1.5 points)
- Hemoptysis (1 point)
- Malignancy (on treatment, treated in the last 6 months or palliative) (1 point)

Reference:
1. Wells PS, Anderson DR, Rodger M, Ginsberg JS, Kearon C, Gent M, et al. Derivation of a simple clinical model to categorize patients probability of pulmonary embolism: increasing the models utility with the SimpliRED D-dimer. Thromb Haemost. 2000;83(3):416-20.