The Pulmonary Embolism Rule-out Criteria (PERC) score
The Setup:
You are working a busy ED shift that has provided you with a variety of chest pain complaints. Your last patient chart is handed to you and the chief complaint is…chest pain. You interview a pleasant 30 year old female who complains of an episode of acute pleuritic chest pain while picking up her 4 year old son two hours ago. She had some mild dyspnea at that time which has since resolved. She is otherwise healthy and takes no medications. Her vital signs and physical exam findings are unremarkable. You think that her symptoms are most likely attributable to musculoskeletal strain and that this is a very low risk presentation for pulmonary embolus (PE).
Despite your risk stratification, you wonder if you should order a d-dimer to rule out PE?
The Study:
Kline JA, Courtney DM, Kabrhel C, Moore CL, Smithline HA, Plewa MC, Richman PB, O’Neil BJ, Nordenholz K. Prospective multicenter evaluation of the pulmonary embolism rule-out criteria. Journal of Thrombosis and Haemostasis. 2008 May;6(5):772-80.
The Big Idea:
PE is the second leading cause of unexplained death in the US (acute coronary syndrome is first). Because of its vague presenting symptoms and potential for significant morbidity and mortality, over-testing to exclude this disorder is commonplace in the ED. Aside from resource overutilization and cost, diagnostic testing for PE is not without complications. Most significantly, chest CTs expose patients to harmful radiation as well as places them at risk for contrast induced nephropathy. D-dimer testing in low-risk individuals has received Level B recommendations from the American College of Emergency Physicians. Unfortunately, the d-dimer is frequently false-positive with multiple confounding variables including advancing age. Furthermore, EP’s rarely compute pre-test probabilities prior to d-dimer ordering despite the availability of validated risk stratification tools. Application of clinical gestalt and the PERC rule offer the potential to minimize diagnostic testing for PE in low risk ED populations. If your clinical suspicion is low and the eight PERC characteristics (Table 1) are absent, you can forgo testing for PE (d-dimer or chest CT).
Table 1
The 8 Components of the PERC Rule
1. Age ≥ 50
2. Pulse ≥ 100
3. RA pulse Ox ≤ 94%
4. Current history of hemoptysis
5. Estrogen use
6. Prior diagnosis of venous thromboembolism
7. Recent surgery or trauma in the last 4 weeks
8. Unilateral leg swelling
The Evidence:
A large randomized controlled trial recently validated the PERC rule which was derived in 2004. This trial enrolled over 8000 patients from 12 EDs in the US and 1 in New Zealand including both urban and community based centers. Patients were eligible if the ED MD ordered a diagnostic test to exclude PE. Physicians were also asked to fill out a standardized data collection form to include their clinical probability for PE (low, moderate, or high risk) before test results were obtained. All patients were followed up at 45 days to determine if they had suffered a PE. In patients that were considered low risk for PE by clinician gestalt (1666 patients), application of the PERC rule would have safely eliminated diagnostic testing in 99%. In other words, applying the PERC criteria to a low risk population of ED patients in whom PE is suspected would result in missing the diagnosis only 1% of the time.
The diagnostic characteristics of the PERC rule are summarized in Table 2 (below).
TABLE 2 Result 95% Confidence
Interval
Sensitivity 97.4% 95.8% to 98.5%
Specificity 21.9% 21.0% to 22.9%
Likelihood Ratio 0.12 0.07 to 0.19
Negative
The Caveats:
Deciding your comfort level with missing a particular disease is important in how decision aids such as the PERC rule are interpreted and implemented. Most would argue that a miss rate of 0% is neither attainable nor reasonable. For disorders that carry significant morbidity and mortality, many physicians would consider a miss rate of 2% or less to be acceptable. While the PERC rule meets this cut off, be sure that your definition of low risk mirrors that of the practicing MDs in this trial.The Outcome: After reviewing the evidence, you are relieved to note that your patient is entirely PERC negative. Combined with your initial clinical gestalt the PERC rule supports your decision to not pursue an evaluation for PE. Two months later, your decision is validated when the patient returns for an unrelated minor injury and has remained healthy.
You are working a busy ED shift that has provided you with a variety of chest pain complaints. Your last patient chart is handed to you and the chief complaint is…chest pain. You interview a pleasant 30 year old female who complains of an episode of acute pleuritic chest pain while picking up her 4 year old son two hours ago. She had some mild dyspnea at that time which has since resolved. She is otherwise healthy and takes no medications. Her vital signs and physical exam findings are unremarkable. You think that her symptoms are most likely attributable to musculoskeletal strain and that this is a very low risk presentation for pulmonary embolus (PE).
Despite your risk stratification, you wonder if you should order a d-dimer to rule out PE?
The Study:
Kline JA, Courtney DM, Kabrhel C, Moore CL, Smithline HA, Plewa MC, Richman PB, O’Neil BJ, Nordenholz K. Prospective multicenter evaluation of the pulmonary embolism rule-out criteria. Journal of Thrombosis and Haemostasis. 2008 May;6(5):772-80.
The Big Idea:
PE is the second leading cause of unexplained death in the US (acute coronary syndrome is first). Because of its vague presenting symptoms and potential for significant morbidity and mortality, over-testing to exclude this disorder is commonplace in the ED. Aside from resource overutilization and cost, diagnostic testing for PE is not without complications. Most significantly, chest CTs expose patients to harmful radiation as well as places them at risk for contrast induced nephropathy. D-dimer testing in low-risk individuals has received Level B recommendations from the American College of Emergency Physicians. Unfortunately, the d-dimer is frequently false-positive with multiple confounding variables including advancing age. Furthermore, EP’s rarely compute pre-test probabilities prior to d-dimer ordering despite the availability of validated risk stratification tools. Application of clinical gestalt and the PERC rule offer the potential to minimize diagnostic testing for PE in low risk ED populations. If your clinical suspicion is low and the eight PERC characteristics (Table 1) are absent, you can forgo testing for PE (d-dimer or chest CT).
Table 1
The 8 Components of the PERC Rule
1. Age ≥ 50
2. Pulse ≥ 100
3. RA pulse Ox ≤ 94%
4. Current history of hemoptysis
5. Estrogen use
6. Prior diagnosis of venous thromboembolism
7. Recent surgery or trauma in the last 4 weeks
8. Unilateral leg swelling
The Evidence:
A large randomized controlled trial recently validated the PERC rule which was derived in 2004. This trial enrolled over 8000 patients from 12 EDs in the US and 1 in New Zealand including both urban and community based centers. Patients were eligible if the ED MD ordered a diagnostic test to exclude PE. Physicians were also asked to fill out a standardized data collection form to include their clinical probability for PE (low, moderate, or high risk) before test results were obtained. All patients were followed up at 45 days to determine if they had suffered a PE. In patients that were considered low risk for PE by clinician gestalt (1666 patients), application of the PERC rule would have safely eliminated diagnostic testing in 99%. In other words, applying the PERC criteria to a low risk population of ED patients in whom PE is suspected would result in missing the diagnosis only 1% of the time.
The diagnostic characteristics of the PERC rule are summarized in Table 2 (below).
TABLE 2 Result 95% Confidence
Interval
Sensitivity 97.4% 95.8% to 98.5%
Specificity 21.9% 21.0% to 22.9%
Likelihood Ratio 0.12 0.07 to 0.19
Negative
The Caveats:
Deciding your comfort level with missing a particular disease is important in how decision aids such as the PERC rule are interpreted and implemented. Most would argue that a miss rate of 0% is neither attainable nor reasonable. For disorders that carry significant morbidity and mortality, many physicians would consider a miss rate of 2% or less to be acceptable. While the PERC rule meets this cut off, be sure that your definition of low risk mirrors that of the practicing MDs in this trial.The Outcome: After reviewing the evidence, you are relieved to note that your patient is entirely PERC negative. Combined with your initial clinical gestalt the PERC rule supports your decision to not pursue an evaluation for PE. Two months later, your decision is validated when the patient returns for an unrelated minor injury and has remained healthy.
Comments
ACADEMIC EMERGENCY MEDICINE 2012; 19:11–17 © 2012 by the Society for Academic Emergency Medicine
Abstract
Objectives: In a patient with symptoms of pulmonary embolism (PE), the presence of an elevated pulse, respiratory rate, shock index, or decreased pulse oximetry increases pretest probability of PE. The objective of this study was to evaluate if normalization of an initially abnormal vital sign can be used as evidence to lower the suspicion for PE.
Methods: This was a prospective, noninterventional, single-center study of diagnostic accuracy conducted on adults presenting to an academic emergency department (ED), with at least one predefined symptom or sign of PE and one risk factor for PE. Clinical data, including the first four sets of vital signs, were recorded while the patient was in the ED. All patients underwent computed tomography pulmonary angiography (CTPA) and had 45-day follow-up as criterion standards. Diagnostic accuracy of each vital sign (pulse rate, respiratory rate, shock index, pulse oximetry) at each time was examined by the area under the receiver operating characteristic curve (AUC).
Results: A total of 192 were enrolled, including 35 (18%) with PE. All patients had vital signs at triage, and 174 (91%), 135 (70%), and 106 (55%) had second to fourth sets of vital signs obtained, respectively. The initial pulse oximetry reading had the highest AUC (0.63, 95% confidence interval [CI] = 0.50 to 0.76) for predicting PE, and no other vital sign at any point had an AUC over 0.60. Among patients with an abnormal pulse rate, respiratory rate, shock index, or pulse oximetry at triage that subsequently normalized, the prevalences of PE were 18, 14, 19, and 33%, respectively.
Conclusions: Clinicians should not use the observation of normalized vital signs as a reason to forego objective testing for symptomatic patients with a risk factor for PE.
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