The Wells score estimates how likely a person's symptoms are to be caused by a pulmonary embolism, based on clinical signs and risk factors, to help decide what testing is needed next.
Low probability (three-tier). PE unlikely by the two-tier model (≤4).
Moderate probability.
PE likely (two-tier) — proceed to imaging.
High probability.
No — it stratifies pretest probability and guides next steps (such as D-dimer testing) rather than excluding PE outright. A low score with a negative D-dimer is what makes PE very unlikely.
The two-tier model splits into PE unlikely (≤4) versus PE likely (>4). The three-tier model uses low (<2), moderate (2–6), and high (>6) probability bands.
Proceed directly to imaging, usually CT pulmonary angiography, rather than relying on a D-dimer, which is less useful once probability is high.
Wells estimates pretest probability; the PERC rule is applied only after a clinician has already judged a patient to be low-risk, to decide whether any testing is needed at all.