What is the Pulmonary Embolism (PE) score using the Pulmonary Embolism Rule-out Criteria (PERC)?

From the Guidelines

The PERC score is a validated clinical decision tool used to safely exclude pulmonary embolism (PE) in low-risk patients without requiring further testing, and it consists of eight clinical variables that must all be met to rule out PE, as outlined in the 2020 European Society of Cardiology guidelines 1. To use the PERC rule, the patient must first be deemed low-risk for PE based on clinical judgment (typically less than 15% pre-test probability).

• The eight PERC criteria are:
  • age less than 50 years
  • heart rate less than 100 beats per minute
  • oxygen saturation greater than 94%
  • no unilateral leg swelling
  • no hemoptysis
  • no recent trauma or surgery
  • no history of venous thromboembolism
  • no hormone use If any single criterion is not met, the PERC rule cannot be used to exclude PE, and further diagnostic testing (typically D-dimer testing) should be pursued, as suggested by the American College of Physicians guidelines 1. The PERC rule works because these eight factors are independently associated with PE, and their absence collectively identifies patients with an extremely low risk (less than 2%) of PE, making further testing unnecessary and potentially harmful due to false positives and unnecessary radiation exposure, as supported by a prospective validation study 1 and a randomized non-inferiority management study 1.
• The use of the PERC rule can decrease the use of D-dimer testing in patients who would have otherwise been tested, rather than increasing d-dimer testing in patients in whom PE is not reasonably suspected, as reported in a large meta-analysis of 12 studies 1. The PERC rule is a useful tool for safely excluding PE in low-risk patients, and its use can help reduce unnecessary testing and potential harm to patients, as recommended by the European Heart Journal 1.

From the Research

PERC Score for Pulmonary Embolism (PE)

The Pulmonary Embolism Rule-out Criteria (PERC) score is a decision aid used to distinguish low-risk from very low-risk PE patients. The key components of the PERC score include:

• Age ≥ 50 years
• Heart rate ≥ 100 beats per minute
• SaO2 < 95% on room air
• Temperature > 38°C
• Immobilization or surgery in the previous four weeks
• Previous deep vein thrombosis or PE
• Hemoptysis
• Malignancy

Application of the PERC Score

Studies have shown that the PERC score can be used to identify patients with a low risk of PE, in whom diagnostic testing may be deferred 2, 3. For example, a study published in the Journal of Emergency Medicine found that the PERC score identified a very low-risk subset of patients with a negative likelihood ratio of 0.17 (95% CI 0.11-0.25) 2. Another study published in the Annals of Emergency Medicine found that the PERC score could be used to determine the testing threshold for PE, and that the average testing threshold was 1.4% across all age and sex cohorts 3.

European Patients with Low Implicit Clinical Probability

A multicentre, prospective, observational study published in The Lancet Haematology found that the PERC rule can exclude PE with a low percentage of false-negative results in European patients with low implicit clinical probability 4. The study found that in patients with a low implicit clinical probability, 337 (32%) patients had negative PERC, of whom four (1.2%; 95% CI 0.4-2.9) went on to have a pulmonary embolism.

Diagnosis of Pulmonary Embolism with d-Dimer Adjusted to Clinical Probability

A prospective study published in The New England Journal of Medicine found that a combination of a low clinical pretest probability and a d-dimer level of less than 1000 ng per milliliter identified a group of patients at low risk for PE during follow-up 5. The study found that none of the 1325 patients who had a low clinical pretest probability and a negative d-dimer test had venous thromboembolism during follow-up (95% CI 0.00 to 0.29%).

Current Evidence and Guideline Recommendations

A review published in Innere Medizin (Heidelberg, Germany) summarizes current evidence and guideline recommendations concerning diagnosis and treatment of deep vein thrombosis and PE 6. The review recommends the use of evidence-based algorithms for the diagnostic pathway, and notes that d-dimer tests may reduce the need for subsequent diagnostic procedures. The review also discusses the importance of risk stratification according to early mortality, and the use of lactate levels for further risk stratification.