Use the Wells score to guide investigation. It does not diagnose PE by itself. First confirm there is a clinical suspicion of PE and assess haemodynamic stability. If the patient is unstable or PE is strongly suspected, involve a senior clinician early and do not delay resuscitation, anticoagulation decisions or urgent imaging while completing decision rules.

For stable adults, use the Wells category with the local PE pathway:

Low probability / PE unlikely: if genuinely low risk, consider PERC. If PERC is not negative or the patient is not suitable for PERC, use a high-sensitivity D-dimer. Age-adjusted thresholds may be used where locally endorsed.
D-dimer negative: PE is usually ruled out and imaging is not required. Reassess for alternate diagnoses.
D-dimer positive or PE likely/high probability: proceed to diagnostic imaging, usually CTPA. Consider V/Q scanning when CTPA is contraindicated or less suitable, such as contrast allergy, significant renal impairment, pregnancy-specific pathways, or selected younger patients with a normal CXR depending on local availability.
Do not use D-dimer alone to exclude PE in high-probability or unstable patients.

This approach is consistent with Australian ED pathways such as the NSW Emergency Care Institute PE evaluation pathway and the Queensland Health ED suspected PE diagnostic pathway.

Wells Criteria for Pulmonary Embolism