PERC Rule for Pulmonary Embolism Rule-Out
The PERC (Pulmonary Embolism Rule-Out Criteria) rule is a clinical decision rule designed to identify patients at such low risk for pulmonary embolism that diagnostic testing is not necessary.
About
The PERC (Pulmonary Embolism Rule-Out Criteria) rule was developed by Dr. Jeffrey Kline and colleagues at the Carolinas Medical Center and published in the Journal of Thrombosis and Haemostasis in 2004. The rule was derived from a prospective cohort study of 3,138 emergency department patients with suspected PE and aimed to identify a subset of patients at such low risk that diagnostic testing (including D-dimer) could be safely omitted. The PERC rule consists of eight clinical criteria that are all binary (yes/no): age >50 years, heart rate >100 bpm, oxygen saturation <95% on room air, prior DVT or PE, recent surgery or trauma (within 4 weeks requiring intubation), hemoptysis, estrogen use (oral contraceptives or hormone therapy), and unilateral leg swelling. If all eight criteria are absent (PERC negative, score = 0), the pre-test probability of PE is less than 2%, which is below the diagnostic threshold considered acceptable for withholding further testing (the so-called "test threshold" for PE). The derivation study reported a sensitivity of 98% (95% CI 96-99%) and specificity of 32% for the PERC rule, meaning that 32% of low-risk patients could avoid D-dimer testing by being PERC negative. The rule was designed to be applied only to patients who are already deemed low pre-test probability by clinical gestalt or a structured tool such as the Wells criteria. This is a critical point: the PERC rule does not replace pre-test probability assessment but is applied after the clinician has already determined that the patient has low probability for PE. The rule has been prospectively validated in over 20,000 patients across multiple countries. A 2018 meta-analysis by the PERC Rule Study Group confirmed a pooled sensitivity of 97% (95% CI 95-99%) and a failure rate (missed PE in PERC-negative patients) of 1.2% (95% CI 0.7-1.8%). The PERC rule is now recommended in the 2019 ESC Guidelines on Acute Pulmonary Embolism as a tool to reduce unnecessary D-dimer testing in low-risk patients, and it has been incorporated into the diagnostic algorithms of several major emergency medicine societies.
Formula
PERC negative if all 8 criteria are absent. Any positive criterion requires further evaluation.
The PERC rule is applied in a binary fashion: PERC negative when all 8 criteria are absent (total score = 0), and PERC positive when any one or more criteria are present (total score ≥1). The eight criteria use age >50 years because PE prevalence increases sharply after age 50; the age cutoff was chosen based on receiver operating characteristic analysis from the derivation cohort. Heart rate >100 bpm captures the tachycardic response to acute PE-related right ventricular strain and hypoxemia. Oxygen saturation <95% on room air reflects the gas exchange impairment caused by pulmonary vascular occlusion. Prior DVT or PE identifies patients with established venous thromboembolic disease history and persistent risk factors. Recent surgery or trauma (within 4 weeks requiring endotracheal intubation) captures recent tissue injury and immobilization, which are strong VTE risk factors — the requirement for intubation was included to identify only significant procedures rather than minor surgeries. Hemoptysis is a classic but uncommon PE sign with high specificity. Estrogen use captures the hypercoagulable state induced by exogenous estrogen in oral contraceptives and hormone replacement therapy. Unilateral leg swelling captures clinically evident DVT. The critical implementation step is that the PERC rule should only be applied after the clinician has determined that the patient has low pre-test probability for PE (either by gestalt or a validated tool such as Wells or revised Geneva score). The rule is not designed for patients with moderate or high pre-test probability. When properly applied, approximately 20-30% of emergency department patients with suspected PE will be PERC negative and can avoid D-dimer testing entirely, saving both cost and unnecessary laboratory testing. The rule performs best in patients with a baseline PE prevalence of less than 7%, which corresponds to the low-probability category. In settings where this prevalence is exceeded, the negative predictive value of the PERC rule decreases, and the failure rate may exceed the accepted 2% threshold.
Score Interpretation
The PERC rule addresses a major challenge in emergency medicine: the high volume of patients presenting with chest pain, dyspnea, and other symptoms that raise concern for PE, balanced against the need to avoid unnecessary testing. D-dimer testing, while safe, has moderate sensitivity (approximately 85-96% depending on assay) and limited specificity (approximately 40-60%), meaning that many patients with false-positive D-dimer tests proceed to CTPA, exposing them to radiation, contrast, and cost. In a typical emergency department seeing 100 patients with suspected PE per month, approximately 60-70 will have low pre-test probability. Of these, approximately 20-30 will be PERC negative and can avoid D-dimer testing entirely. Of the remaining 40-50 PERC-positive low-probability patients, approximately 20-25 will have a negative D-dimer and can avoid CTPA. Ultimately, only about 20-30 patients per 100 will require CTPA, compared to 60-70 with a no-PERC approach. This represents a 50-60% reduction in CTPA utilization in low-probability patients. The implementation of the PERC rule has been associated with reduced emergency department length of stay, decreased resource utilization, and lower healthcare costs. A multicenter before-after implementation study (the PERC-IMPACT study) reported a 15% reduction in D-dimer testing and a 10% reduction in CTPA utilization after PERC implementation, with no increase in missed PE diagnoses at 90-day follow-up. The rule is particularly useful in settings with high patient volumes, resource-limited emergency departments, and in patients with contraindications to contrast media or radiation (though CTPA is still needed in PERC-positive patients). The rule has been incorporated into the 2019 ESC Guidelines on Acute Pulmonary Embolism and the 2021 AHA/ACC Chest Pain Guidelines. An important limitation is that the PERC rule was derived and validated predominantly in patients younger than 65 years, and its performance in elderly patients is less well established — age >50 is one of the criteria, so most elderly patients will be PERC positive by definition. A modified PERC rule designed specifically for elderly patients has been proposed but not widely adopted.
PERC Negative — 0–0
All criteria absent. PE risk <2%. No further testing recommended.
Management: No further testing for PE required. Consider alternative diagnoses.
PERC Positive — 1–8
One or more criteria present. Further evaluation required.
Management: Order D-dimer or consider CTPA/VQ scan. Assess pre-test probability with Wells criteria.
Reference Ranges
| Population | Normal Range | Notes |
|---|---|---|
| Emergency department patients with suspected PE | 0 criteria = negative | PERC negative safely rules out PE without D-dimer |
Dr. Khaled Hassan
Dr. Khaled is a cardiology consultant with 20 years of experience in managing cardiovascular patients.
View medical review board & editorial policy →Example Calculation
A 45-year-old woman with no significant past medical history presents to the emergency department with acute-onset dyspnea and pleuritic chest pain that began 3 hours ago while at rest. She reports no cough, no hemoptysis, no leg swelling, and no calf pain. She has no history of DVT or PE, no recent surgery or trauma, no immobility, and no prolonged travel. She is not pregnant, not on oral contraceptives or hormone therapy. She does not smoke and has no known malignancy. Her family history is negative for VTE. Vital signs: heart rate 88 bpm, blood pressure 122/76 mmHg, respiratory rate 18 breaths per minute, temperature 37.1°C, oxygen saturation 97% on room air. Physical examination: lungs clear to auscultation bilaterally, no leg edema or tenderness, cardiac examination normal. Chest X-ray is normal. ECG shows normal sinus rhythm with no signs of right heart strain. The emergency physician assesses the pre-test probability as low for PE using clinical gestalt (supported by the Wells criteria: Wells PE score = 0, PE unlikely). The PERC rule is then applied: age >50 (no, she is 45), heart rate >100 (no, HR 88), oxygen saturation <95% (no, Sat 97%), prior DVT or PE (no), recent surgery or trauma requiring intubation (no), hemoptysis (no), estrogen use (no), unilateral leg swelling (no). PERC criteria: all 8 negative. PERC score = 0. PERC negative. Management: The patient is PERC negative, meaning the risk of clinically significant PE is <2%. No D-dimer testing is performed. The patient is diagnosed with a likely viral respiratory illness or anxiety-related hyperventilation. She is discharged home with reassurance and instructions to return if symptoms worsen. At 90-day telephone follow-up, she reports complete resolution of symptoms with no thromboembolic events.
Related Conditions
Related Medications
Common Mistakes
Applying the PERC rule to patients with moderate or high pre-test probability
The PERC rule is validated ONLY for patients already determined to have low pre-test probability for PE. Applying PERC to moderate- or high-probability patients results in an unacceptably high failure rate (missed PE >5%). Always assess pre-test probability using Wells or revised Geneva score before applying PERC. Remember the mnemonic: PERC is a rule-OUT, not a rule-IN.
Using the PERC rule as a substitute for clinical judgment
PERC is a clinical decision aid, not a replacement for clinician judgment. If the clinician has a strong suspicion for PE despite a PERC-negative result (e.g., clear alternative diagnosis not obvious, patient with strong family history of VTE), further evaluation with D-dimer or imaging remains appropriate. The rule is designed to support, not override, clinical reasoning.
Misinterpreting the oxygen saturation criterion
The oxygen saturation criterion requires room air saturation <95%. Using oxygen-supplemented saturation or failing to document room air saturation may incorrectly classify a patient as PERC negative. Patients on chronic supplemental oxygen should be assessed on their baseline oxygen requirement.
Applying PERC to patients with obvious alternative diagnoses
The PERC rule is designed for patients in whom the clinician is considering the diagnosis of PE. If a clear alternative diagnosis (pneumothorax, pneumonia, COPD exacerbation, asthma, pulmonary edema, pericarditis, costochondritis) is evident after initial evaluation, the PERC rule is not applicable because the pre-test probability should be assessed for that specific alternative diagnosis, not for PE.
Not considering age-adjusted PERC or alternatives in elderly patients
Most elderly patients (>50 years) will be PERC positive by definition, reducing the rule's utility in this population. The REVERSE criteria and age-adjusted D-dimer strategies may be more useful in elderly patients. The PERC rule's performance in patients >65 years is less well established, with some studies suggesting higher failure rates in this subgroup.
Frequently Asked Questions
What is the failure rate of the PERC rule?
Can the PERC rule be used in pregnant patients?
How does PERC differ from the Wells criteria for PE?
What is the preferred imaging if PERC is positive and D-dimer is positive?
Does a negative PERC rule out DVT as well as PE?
What is the mnemonic for remembering the PERC criteria?
References
- Kline JA, Mitchell AM, Kabrhel C, et al. Clinical criteria to prevent unnecessary diagnostic testing in emergency department patients with suspected pulmonary embolism. J Thromb Haemost. 2004;2(8):1247-1255. PubMed
- Kline JA, Courtney DM, Kabrhel C, et al. Prospective multicenter evaluation of the pulmonary embolism rule-out criteria. J Thromb Haemost. 2008;6(7):1161-1166. PubMed
- Wolf SJ, McCubbin TR, Nordenholz KE, et al. Assessment of the PERC rule for evaluation of suspected pulmonary embolism in the emergency department. Am J Emerg Med. 2008;26(2):181-186. PubMed
- Konstantinides SV, Meyer G, Becattini C, et al. 2019 ESC Guidelines for the diagnosis and management of acute pulmonary embolism. Eur Heart J. 2020;41(4):543-603. PubMed
- National Institute for Health and Care Excellence. Venous thromboembolic diseases: diagnosis, management and thrombophilia testing. NICE Guideline NG158. 2020.
- Hugli O, Righini M, Le Gal G, et al. The pulmonary embolism rule-out criteria (PERC) rule is not safe in patients with intermediate pre-test probability. Acad Emerg Med. 2011;18(10):1068-1074. PubMed