PERC

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Kline JA, et al. "Prospective multicenter evaluation of the pulmonary embolism rule-out criteria". J Thromb Haemost. 2008. 6(5):772-780.
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Clinical Question

In low-risk outpatients with suspected pulmonary embolism (PE), can the application of the pulmonary embolism rule-out criteria (PERC) predict venous thromboembolism (VTE) and all-cause mortality rates at 45 days of less than 2%?

Bottom Line

In outpatients presenting with a symptom for which PE is a consideration, a low pretest probability of PE as judged by clinical gestalt and a reassuring PERC score is associated with a very low probability (<2%) of VTE or all-cause mortality at 45 days.

Major Points

Excessive investigation for pulmonary embolism (PE) in low-risk patients has resulted in increased radiation exposure from CT angiography. The Pulmonary Embolism Rule-Out Criteria (PERC) study was a large prospective multicenter validation study evaluating the whether a low clinical suspicion and reassuring PERC score[1] could predict a low rate of VTE or all-cause mortality at 45 days among patients who did not undergo CT angiography. In patients presenting with symptoms concerning for PE, PE or death within 45 days of enrollment occurred in only 1% of patients deemed low risk by clinical gestalt and a negative PERC score. This was beneath the 2% threshold chosen by the investigators — this was selected as the point of equipoise, the point at which the risk/benefit of investigating for PE is balanced with the risk/benefit of not investigating.

Design

  • Multicenter, prospective, cohort study
  • N=8,138 patients with possible PE
  • Setting: 12 emergency departments in the US, and one in New Zealand
  • Enrollment: 2003-2006
  • Follow-up: 45 days
  • Primary outcome: VTE or all-cause mortality at 45 days

Population

Inclusion Criteria

  • Initiation of diagnostic testing for suspected PE (CTA, VQ lung scanning or a D-dimer assay); DVT ultrasound did not trigger enrollment

Exclusion Criteria

  • Recent imaging diagnosis of PE within last 7 days
  • Patient preferred to follow-up at another hospital
  • High risk circumstances in which patient may be lost to follow-up (eg, lack of housing, severe mental illness)

Original PERC Study Exclusion Criteria

For comparison, the original PERC study excluded patients with the following characteristics:

  • Shortness of breath is not the most important or equal most important presenting complaint
  • Active malignancy
  • Known thrombophilia
  • Strong family history of thrombosis
  • Concurrent beta-blocker use (that could blunt reflex tachycardia)
  • Transient tachycardia
  • Patients with amputations
  • Massively obese patients in which unilateral leg swelling cannot be assessed
  • Patients with baseline SpO2 <95%

Baseline Characteristics

  • Mean age: 49 years
  • Gender: 67% female
  • Race: Black (32%), Caucasian (59%), Latino or Hispanic descent (6%)
  • Symptoms
    • Pleuritic chest pain: 44%
    • Substernal chest pain: 34%
    • Dyspnea: 51%
    • Cough: 29%
    • Syncope: 6%
    • Hemoptysis: 3%
  • Comorbidities
    • Current smoker: 35%
    • Active malignancy: 15%
    • Immobility: 25%
    • Recent surgery: 7%
    • Pregnant or post-partum (<4 weeks): 10%
    • Prior PE or DVT: 11%
    • Congestive heart failure: 10%
    • Chronic obstructive pulmonary disease: 6%
    • Coronary artery disease: 13%
    • Taking warfarin: 7%
    • Hematologic thrombophilia: 5%
    • Connective tissue disease: 7%
    • Exogenous estrogen: 11%
  • Physical Findings
    • Highest pulse rate (beats per minute): 92
    • Highest respiratory rate (breaths/min): 21
    • Lowest SBP (mmHg): 131
    • Lowest pulse oximetry at room air (%): 96
    • Mean temperature (degrees celsius): 37
    • Wheezing: 10%
    • Unilateral leg swelling: 9%

Interventions

  • This was a prospective non-interventional trial.
  • Patients presented to the ED and were managed accordingly by clinicians.
  • Patients who met eligibility criteria were followed by the study team, who collected data regarding their course, and obtained 45-day follow-up information.
  • Treating clinicians provided their pretest probability of PE based on clinical gestalt, and PERC criteria were recorded as well.

PERC criteria

PERC-negativity requires the clinician to answer No for all eight of the following criteria:[2]

  • Age >49 years?
  • Heart rate >99 beats per minute?
  • SpO2 <95% on room air?
  • Active hemoptysis?
  • Taking estrogen?
  • Prior VTE?
  • Recent surgery/trauma requiring hospitalization within prior 4 weeks?
  • Unilateral leg swelling?

Outcomes

Primary Outcomes

VTE or death from any cause in low-risk patients (by clinical gestalt and PERC-negative) at 45 days
1,666 out of 8,138 patients were considered low risk for PE and were PERC-negative.
  • 15 had VTE and 1 died out of the 1,666.
  • False negative rate of 16/1,666 = 1.0%

Secondary Outcomes

VTE at 45 days
6.9%
Death from PE at 45 days
1 of 561

Criticisms

  • Clinical gestalt was required to determine pretest probability. (This might decrease generalizability, but it's also a strength of the study since clinical gestalt is a critical part of day-to-day practice.)
  • Prevalence of PE in the study population was relatively low, at 5.9% within 45 days. The <2% rate of VTE or all-cause mortality observed in this study may not be generalizable to centers with higher rates of PE.

Funding

  • The study received government funding through the Grants from the National Institutes of Health. Additional funding included a Medical Student Award from the Emergency Medicine Foundation.
  • J. A. Kline owns stock in CP Diagnostics LLC and Studymaker LLC. C. L. Johnson owns stock in CPDiagnostics LLC and Studymaker LLC.

Further Reading