It is important to diagnose pulmonary embolism in a timely manner to prevent death and long-term disability. More than half a million people (4-5% of emergency department patients) are tested for pulmonary embolism, although the positive rate is low. Imaging for PE testing exposes patients to radiation, is expensive, adds time to the emergency visit, and can lead to a false positive diagnoses. Existing protocols aimed at reducing unnecessary pulmonary embolism imaging are complex and seldom used by emergency physicians. Too many patients undergo unnecessary pulmonary embolism imaging.

A new tool (called Adjust-Unlikely) could safely reduce pulmonary embolism imaging in Canada. A research group composed of researchers, emergency physicians, and patients developed the Adjust-Unlikely clinical decision rule: a rule which has been customized for emergency physicians and emergency patients. Adjust-Unlikely is highly sensitive at the bedside, meaning there are very few false negative results.

The study aim is to prospectively validate Adjust-Unlikely pulmonary embolism testing in emergency patients with suspected pulmonary embolism.

Inclusion Criteria:

• Emergency department patient who is tested by an emergency physician for PE

Exclusion Criteria:

• Patient is < 18 years of age
• No documentation of whether PE is the most likely diagnosis
• D-dimer is not tested or else not resulted during the emergency visit
• The D-dimer level is known before documentation of whether PE is the most likely diagnosis
• The D-dimer is ordered prior to the physician assessing the patient
• The patient has previously registered that they opt out of all research at the participating site
• The patient leaves against medical advice
• The patient has had PE or deep vein thrombosis imaging (CT pulmonary angiogram, ventilation-perfusion scan or lower limb ultrasound) within prior 30 days
• There is a new (non-PE) indication for anticoagulation
• The patient was initiated on treatment for presumed PE prior to PE testing
• The patient has previously been enrolled into the study
• The patient has a prior history of lower extremity deep vein thrombosis without availability of a baseline ultrasound scan
• The patient was transferred from another hospital organization
• The patient does not reside in Ontario
• The patient has no valid Ontario Health Insurance Plan card

Emergency department patient who is tested by an emergency physician for PE.