Pulmonary Embolism

Wells’ Criteria for Pulmonary Embolism⁴

Score <2: 1.3% incidence of PE. You can consider using a rule-out strategy such as the PERC score. If a D-Dimer is negative consider stopping workup. If positive, consider moving to imaging such as V/Q scanning or CTPA.
Score 2–6: 16.2% incidence of PE. Consider D-dimer testing or CTPA. If D-dimer is negative consider stopping workup, if the D-dimer is positive consider CTPA
Score >6: 37.5% of PE. D-dimer is not recommended; consider CTPA.

Some have argued for the use of a simplified two-tier scoring model⁵. If a patient scores <4, you would consider D-dimer, and if negative, consider stopping work-up. If a patient scores >4, a D-dimer is not recommended and V/Q scanning or CTPA should be considered.

PERC Score⁶

The rule comprises eight components which must all be negative in order to exclude PE in a patient with a low (<15%) pre-test probability. The PERC rule is useful when PE is considered as a cause for patients’ presentation, but felt by the clinician to be unlikely either through gestalt or through use of risk assessment tools such as the Wells’ criteria.

The authors of the PERC rule classified patients into “low risk” patients, with a clinical suspicion of PE meeting PERC criteria and ‘very low risk’ patients where PE was not suspected and in whom PERC criteria were met. Using PERC, PE cannot be ruled out if any of the following are present:

• Age ≥ 50
• HR ≥100
• O2 sats ≤95% on room air
• Unilateral leg swelling
• Haemoptysis
• Recent trauma or surgery
• Prior PE or DVT
• Exogenous hormone use

Revised Geneva Score⁷

Score <3: <10% incidence of PE.
Score 4-10: If D-dimer is positive, consider imaging.
Score >11: >60% incidence of PE – consider imaging.

The Wells’ Score has a sensitivity of 63.8%–79.3% and specificity of 48.8%–90%. The revised Geneva has a Sensitivity of 55.3%–73.6%7. This reduced sensitivity may result from the Revised Geneva Score not involving gestalt, which some argue is better than use of a CDR.

The Pulmonary Embolism Rule-out Criteria (PERC) Clinical Decision Rule is for use in patients deemed to be at low risk of Pulmonary Embolism. With this tool, low risk patients can have PE ruled out using clinical history and examination findings alone, thus minimising need for blood testing and imaging. As a rule-out test, PERC is highly sensitive (96%–100%) but poorly specific (27%) for PE, and the authors describe it as a tool to ‘complement clinical judgement’ rather than replace it⁶.

It should be noted that immobility, a recognised risk factor for VTE, is not included in the PERC score, nor is symptom onset, whether that be gradual or sudden. The authors of the rule noted a low inter-observer agreement regarding to immobility leading to it being excluded from the rule. Interestingly, in the original derivation group for the PERC score, sudden onset of symptoms was noted to be a negative predictor of VTE, in contrast to previously published evidence identifying sudden onset of dyspnoea as a positive predictor for PE⁸.