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Diagnostic algorithm for suspected pulmonary embolism

Suspected pulmonary embolism is a common diagnostic conundrum in the ED and MAU. This algorithm provides a simple logical approach which should improve diagnostic efficiency and effectiveness. It is based on more extensive guidelines published by the British Thoracic Society in 2003. It should only be used when there is a reasonable possibility that pulmonary embolism could explain the patient's presenting symptoms and signs, and there is no other likely possibility.

In brief, patients should first have:

1. a good quality departmental PA chest radiograph
2. a full evaluation by an experienced middle grade doctor or consultant, so that alternative diagnoses have been carefully considered, and
3. a formal clinical probability calculated and recorded

Only if the pre-test probability is low or intermediate should a D-dimer test then be performed. The result of this will determine if lung scanning should be undertaken, as indicated by the flow chart. In Oxford, isotopic lung perfusion (Q) scanning is used unless the chest radiograph is abnormal or there is a history of COPD or asthma, when CTPA is more appropriate.

Calculating clinical probability

(After Wells: Thrombosis & Haemostasis 2000 83:416-20)

Active cancer (treatment within 6mo or palliative)	1
Surgery or bedridden for >=3d in past 4 weeks	1.5
History of DVT or PE	1.5
Haemoptysis	1
Heart rate >100 bpm	1.5
PE judged the most likely diagnosis	3

Probability from total score is: ≤4 = PE unlikely, >4 PE likely