Unifying Concepts

Pulmonary Embolism Rule-out Criteria (PERC)

The pulmonary embolism rule-out criteria (PERC) was designed to identify patients in whom the risk of testing outweighs the benefits (the “test threshold”, which for pulmonary embolism (PE) was calculated as a 2% prevalence).

The PERC consists of eight objective variables that can be applied to patients with low clinical (pre-test) probability of PE. The sensitivity of the PERC rule is 96% to 100% and specificity is 15% to 27%.


  1. Age <50 yr
  2. Pulse <100 bpm
  3. SaO2 >94%
  4. No unilateral leg swelling
  5. No hemoptysis
  6. No recent trauma or surgery
  7. No prior pulmonary embolism/ deep venous thrombi
  8. No hormone use

The PERC rule has not been validated for people with:

  • Active cancer, thrombophilia or a strong family history of thrombophilia
  • Transient tachycardia or beta-blocker use that may mask tachycardia
  • Leg amputations
  • Morbid obesity (leg swelling not easily determined)
  • Baseline hypoxaemia when oximetry reading <95% is longstanding.

If the patient’s PERC score is >0, then an enzyme-linked immunosorbent assay (ELISA)-type D-dimer is recommended. If this is negative, pulmonary embolism is ruled out and no further investigation is required; if positive, then imaging is recommended.



  1. Corrigan D, Prucnal C, Kabrhel C. Pulmonary embolism: the diagnosis, risk-stratification, treatment and disposition of emergency department patients. Clin Exp Emerg Med. 2016 Sep 30;3(3):117-125. [Medline]
  2. Doherty S. Pulmonary embolism An update. Aust Fam Physician. 2017 Nov;46(11):816-820. [Medline]


Created Oct 25, 2019.

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