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

From the Guidelines

The PERC score should be used to rule out pulmonary embolism in low-risk patients, as it has been shown to decrease the use of d-dimer testing by 22% while missing only 0.3% of PEs, according to a recent large meta-analysis of 12 studies 1.

Key Points to Consider

• The PERC score is a clinical decision tool used to safely rule out pulmonary embolism (PE) in low-risk patients without requiring further diagnostic testing.
• To use the PERC rule, the patient must first be deemed low-risk for PE based on clinical judgment.
• If the patient meets all eight PERC criteria (age <50, heart rate <100, oxygen saturation ≥95%, no unilateral leg swelling, no hemoptysis, no recent trauma or surgery, no history of PE or DVT, and no hormone use), PE can be safely ruled out without additional testing like D-dimer or imaging.
• The PERC rule has a high negative predictive value, meaning when all criteria are met, the risk of PE is less than 2%, which is lower than the test threshold for pursuing further workup.

Benefits of Using PERC Score

• Reduces unnecessary testing, radiation exposure, and healthcare costs while maintaining patient safety.
• Decreases the use of d-dimer testing by 22% while missing only 0.3% of PEs, as shown in a recent large meta-analysis of 12 studies 1.

Important Considerations

• PERC should only be applied to patients already considered low-risk based on clinical assessment.
• It cannot be used to rule out PE in moderate or high-risk patients.
• The low specificity of d-dimer testing has also resulted in changes to the acceptable normal ranges of the plasma test, with some studies using age-adjusted d-dimer cutoffs to increase specificity while maintaining sensitivity above 97% 1.

From the Research

PERC Score Overview

• The Pulmonary Embolism Rule-out Criteria (PERC) score is a clinical diagnostic rule designed to exclude pulmonary embolism (PE) without further testing 2.
• The PERC rule consists of eight criteria, and patients who meet all eight criteria are considered to be at a very low risk for PE 3.

Diagnostic Performance of PERC

• The diagnostic performance of the PERC rule has been evaluated in several studies, with varying results 2, 3, 4, 5, 6.
• A systematic review and meta-analysis found that the PERC rule had a high sensitivity (0.97) and low specificity (0.23) for ruling out PE 4.
• Another study found that the PERC rule had a negative likelihood ratio of 0.21 for predicting PE overall, and 0.63 in low-risk patients 2.

Comparison with D-Dimer Testing

• The PERC score has been compared to D-dimer testing in low-risk patients for PE, with some studies suggesting that the PERC score may be more effective in ruling out PE 5, 6.
• A retrospective study found that D-dimer testing in PERC-negative patients led to a diagnosis of PE in 0.5% of cases, with 15% of patients undergoing unnecessary irradiative imaging studies 5.
• Another study found that combining positive D-dimer and PERC results resulted in a sensitivity of 100% and a specificity of 23% for ruling out PE 6.

Clinical Implications

• The PERC rule may be useful in identifying low-risk patients who do not require further testing for PE 3, 6.
• However, the rule should be used in conjunction with clinical judgment and other diagnostic tools to ensure accurate diagnosis and treatment of PE 2, 4.
• Proper use of the PERC rule may significantly reduce patients' waiting time in the emergency department 6.