17th January 2024

Clinical scoring tools

Wells’ score for PE 

A risk stratification tool that determines recommended further investigations when used in the presence of clinical suspicion of PE. A score of >4 indicates that PE is likely and the clinician should proceed directly to CT pulmonary angiogram (CTPA), whilst a score of 4 or less suggests PE is less likely and that a d-dimer blood test should first be performed. If the d-dimer result is then negative, PE can be ruled out, whilst a positive d-dimer result would indicate further investigation +/- treatment is required. 

Table 1 – Wells’ score for PE. 

Pulmonary Embolism rule-out criteria (PERC score)

The PERC score is strictly a rule-out criteria in patients who have a low pre-test probability of PE. When used in the correct patient group, a PERC score of 0 indicates the clinician can safely rule out a PE without the need for further investigations. Scoring even a single point means the PERC rule cannot be used to rule out PE, but importantly, it cannot be used to make a positive diagnosis in itself. 

Table 2 – PERC rules.

Table 1 Source: Wells’ Criteria for DVT – MDCalc [Internet]. Available from: https://www.mdcalc.com/wells-criteria-dvt

Table 2 Source: PERC Rule for Pulmonary Embolism – MDCalc [Internet]. Available from: https://www.mdcalc.com/perc-rule-pulmonary-embolism

Investigations

• Blood tests
  • Full blood count (FBC)
  • Clotting screen
  • Urea and electrolytes (U&Es) – important in particular when considering whether the patient is fit for a CTPA with contrast
  • D-dimer – only to be used in patients with a low pre-test probability
  • Troponin – to help risk stratify
• Arterial blood gas sampling – look for hypoxia and hypocapnia
• Electrocardiogram (ECG) – features include:
  • Sinus tachycardia
  • Right bundle branch block (RBBB)
  • S1Q3T3 – Deep S-waves in lead I, pathological Q-waves in lead III, inverted T-waves in lead III
  • T-wave inversion in V1-V3 (right ventricular strain pattern)
  • P pulmonale

Image Source: Wikimedia Commons (2010). Pulm_embolism, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Pulm_embolism.jpg (Accessed: 5 June 2022).

• Imaging 
  • Chest x-ray (CXR)– useful to exclude alternative diagnoses, and a normal CXR is also a prerequisite for interpreting a ventilation/perfusion (V/Q) scan.
  • CT pulmonary angiogram (CTPA) – the main imaging modality of choice to look for filling defects associated with large or subsegmental PEs.
  • Ultrasound doppler – not a direct diagnostic test for PE, but sometimes used to identify lower limb DVTs in patients where ionising radiation is contraindicated (i.e., in pregnancy). If a VTE elsewhere is identified, and the patient has the classical signs and symptoms, treatment can be started empirically.
  • Ventilation/perfusion (V/Q) scanning – imaging using radioisotopes to identify any areas of mismatch in ventilation and perfusion of the lungs.
  • Transthoracic echocardiogram – not part of the formal diagnostic pathway, but can be used as adjunctive imaging to identify features of right heart strain, such as right ventricular dilatation and a poorly compressible internal vena cava (IVC) (3).

A CTPA demonstrating a saddle pulmonary embolus with thrombus visualised below in pulmonary arteries bilaterally. Myat A, Ahsan A

Image Source: Wikimedia Commons (2007). Pulmonary embolism CTPA, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Pulmonary_embolism_CTPA.JPEG (Accessed: 5 June 2022).

• Imaging
  • Chest x-ray (CXR)– useful to exclude alternative diagnoses, and a normal CXR is also a prerequisite for interpreting a ventilation/perfusion (V/Q) scan.
  • CT pulmonary angiogram (CTPA) – the main imaging modality of choice to look for filling defects associated with large or subsegmental PEs.
  • Ultrasound doppler – not a direct diagnostic test for PE, but sometimes used to identify lower limb DVTs in patients where ionising radiation is contraindicated (i.e., in pregnancy). If a VTE elsewhere is identified, and the patient has the classical signs and symptoms, treatment can be started empirically.
  • Ventilation/perfusion (V/Q) scanning – imaging using radioisotopes to identify any areas of mismatch in ventilation and perfusion of the lungs.
  • Transthoracic echocardiogram – not part of the formal diagnostic pathway, but can be used as adjunctive imaging to identify features of right heart strain, such as right ventricular dilatation and a poorly compressible internal vena cava (IVC) (3).

Image Source: Wikimedia Commons (2007). Pulmonary embolism CTPA, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Pulmonary_embolism_CTPA.JPEG (Accessed: 5 June 2022).