Investigations

The investigations required are outlined below.

Chest radiograph

A chest radiograph should be requested for all patients with a suspected PE. It is usually normal or may reveal non-specific changes such as small pleural effusion. Rarely, a wedge shaped pulmonary infarction or regional oligaemia (Westermark sign) may be seen.

Click on the x-ray to enlarge.

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The main purpose of the chest radiograph is to exclude alternative diagnosis, for example, pneumothorax or infection which may give rise to the same presenting symptoms.

12-lead ECG

An ECG should be obtained to look for signs supportive of right heart strain such as right axis deviation, and to rule out an acute coronary syndrome. The most common ECG finding is a sinus tachycardia. Atrial fibrillation is present in approximately 20% of cases.

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The classical S1 Q3 T3 pattern (right) is present in only ~10% of patients with PE.

Blood tests

• Arterial Blood Gas (ABG): ABG analysis may confirm hypoxia, evidence of hyperventilation and an increased Arterial-alveolar gradient. Whilst supportive of a pulmonary embolism these features are not exclusive to this condition and may be found in conditions such as pneumonia.

• Full blood count: A full blood count may reveal a marked neutrophilia which may suggest a diagnosis of infection rather than infarction.

• Cardiac troponin: Troponin levels may be elevated in acute PE, particularly massive PE. High levels suggest right ventricular strain or overload and can be helpful in prognosis and risk stratification (e.g. as an aid to decision making for thrombolysis in PE), but are not useful in the diagnosis of PE⁸.

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Neither a chest radiograph nor any of the tests listed above are sensitive or specific enough to rule in or exclude a diagnosis of PE.