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Results from the PROPER Trial: What are the Pulmonary Embolism Rule-Out Criteria (PERC) and Do They Really Work?


  • The Pulmonary Embolism Rule-Out Criteria (PERC), an 8-item set of clinical criteria that serves as a predictive tool, has not been evaluated using a randomized trial (RCT)  
  • Each PERC criteria is scores as ‘0’ (no) or ‘+1’ (yes) and a 0 score indicates no further work-up is needed, with a <2% chance of PE  
  • Arterial oxygen saturation (Sp02) of ≤94% 
  • Pulse rate of at least 100/min 
  • Patient age of 50 years or older 
  • Unilateral leg swelling 
  • Hemoptysis 
  • Recent trauma or surgery 
  • Prior PE or deep venous thrombosis (DVT) 
  • Exogenous estrogen use 
  • Freund et al. (JAMA, 2018) aimed to validate the safety of the PERC-based strategy to exclude PE 


  • noninferiority, crossover cluster randomized controlled trial  
  • 14 EDs in France were involved for two 6-month periods separated by a 2-month washout period 
  • Patients who came to the ED with a suspicion of PE were eligible  
  • Inclusion criteria included  
    • new-onset presence or worsening of shortness of breath or chest pain  
    • Low probability of PE (clinician’s pre-test probability is <15%), based on physicians unstructured impression of risk (low, moderate, or high) 
      • Evidence that unstructured ‘gestalt’ performs as well as structured assessment 
  • Each center was randomized to determine sequence of intervention periods 
  • During the PERC period, the diagnosis of PE was excluded with a PERC score of 0, with no further follow up  
  • During the non-PERC period, usual diagnostic strategy was followed for low level of suspicion for PE 
    • D-dimer testing 
    • If D-dimer testing is positive, computed tomographic pulmonary angiography (CTPA) was performed 
    • If both negative, PE was ruled out and no further follow-up  
  • Primary outcome 
    •  Percentage of failure of the diagnostic strategy 
  • Secondary outcomes  
    • Rate of CTPA use  
    • Median length of stay in the emergency department 
    • Rate of hospital admission 


  • 1916 patients were cluster-randomized (mean age 44 years, 980 [51%] women) 
    • 962 were assigned to the PERC group 
    • 954 were assigned to the control group 
    • A total of 1,749 patients completed the trial 
  • A PE was diagnosed at initial presentation in  
    • 26 (2.7%) of patients in the control group vs 14 (1.5%) in the PERC group 
      • Mean difference, 1.3% (95% CI, −0.1% to 2.7%; P = .052) 
  • Primary outcome: One symptomatic PE (0.1%) at 3 months was diagnosed during follow-up in the PERC group vs none in the control group 
  • The proportion of patients undergoing CTPA in the PERC group vs control group was 13% vs 23%  
    • Mean difference, 9.7% (95% CI, 6.1% to 13.2% P < .001) 
  • In the PERC group 
    • Median length of emergency department stay rates were significantly reduced  
      • Mean reduction, 36 minutes (95% CI, 4 – 68)  
    • Hospital admission rates were significantly reduced (13% vs 16%)  
      • Mean difference, 3.3% (95% CI, 0.1% to 6.6%) 


  • Among low-risk patients for PE, using the PERC strategy did not result in an inferior rate of thromboembolic events over 3 months 
  • Authors point out limitations of this study, including low initial prevalence of PE at 2.7% and may be explained by low average age  
  • This study supports the use of PERC for very low-risk patients presenting at the emergency department 

Learn More – Primary Sources: 

Effect of the Pulmonary Embolism Rule-Out Criteria on Subsequent Thromboembolic Events Among Low-Risk Emergency Department Patients The PROPER Randomized Clinical Trial