About the Wells PE Score
The Wells Score for Pulmonary Embolism is the most widely used clinical prediction rule for estimating pre-test probability of PE. Published by Wells et al. in 1998 and validated extensively, it stratifies patients into low, moderate, or high probability categories to guide the diagnostic workup.
3-Level Stratification
| Score | Category | PE Prevalence | Strategy |
|---|---|---|---|
| <2 | Low | ~2% | D-dimer; if negative, PE excluded |
| 2–6 | Moderate | ~17% | D-dimer; if positive, CTPA |
| >6 | High | ~40–66% | CTPA directly (skip D-dimer) |
2-Level (Dichotomized) Stratification
| Score | Category | Strategy |
|---|---|---|
| ≤4 | PE Unlikely | High-sensitivity D-dimer; if negative, PE excluded |
| >4 | PE Likely | CTPA (do not rely on D-dimer) |
CTPA vs D-Dimer Decision
The key clinical choice is whether to order a D-dimer or go straight to CT pulmonary angiography (CTPA). D-dimer is highly sensitive (~97%) but not specific — it is elevated in many non-PE conditions (infection, cancer, surgery, pregnancy). Its utility lies in its negative predictive value: a negative D-dimer in a low/moderate probability patient effectively excludes PE.
In high probability patients (Wells >6 or 2-level "PE Likely"), CTPA should be performed without waiting for D-dimer, as a negative D-dimer does not reliably exclude PE in this population.
References
Wells PS, et al. Derivation of a simple clinical model to categorize patients probability of pulmonary embolism. Thromb Haemost. 1998;83:416–420.
van Belle A, et al. (Christopher Study Investigators). Effectiveness of managing suspected pulmonary embolism using an algorithm combining clinical probability, D-dimer testing, and computed tomography. JAMA. 2006;295:172–179.