Printed on 3/17/2026
For informational purposes only. This is not medical advice.
The Pulmonary Embolism Rule-out Criteria (PERC) is a clinical decision tool designed to identify patients in whom pulmonary embolism can be safely excluded without D-dimer testing. If a clinician's pre-test probability is low AND all eight PERC criteria are negative, PE can be ruled out without further testing. This reduces unnecessary D-dimers, CT scans, and radiation exposure.
Formula: All 8 criteria must be negative to rule out PE (binary yes/no)
Before applying PERC, you must determine that the patient's pre-test probability of PE is LOW (typically <15% by clinical gestalt or [Wells PE Score](/tools/wells-pe-score) <2). This is the most critical step. PERC should NEVER be applied to patients with moderate or high suspicion for PE. Ask yourself: 'Is PE unlikely in this patient?' If you're genuinely worried about PE, don't use PERC — proceed directly to Wells PE Score and D-dimer. PERC is designed to safely avoid testing in patients where PE is being considered but is not a leading diagnosis. Document your pre-test probability assessment in the medical record.
Evaluate each of the eight criteria carefully: age ≥50, heart rate ≥100 bpm, oxygen saturation <95% on room air (critical: must be room air, not on supplemental oxygen), hemoptysis (any amount, including blood-streaked sputum), estrogen use (oral contraceptives, hormone replacement, pregnancy, or other estrogen therapy), prior history of DVT or PE (any prior episode, even if provoked), unilateral leg swelling (objective finding on exam, not just patient-reported leg pain), and surgery or trauma requiring hospitalization within the past 4 weeks (major procedures only; outpatient procedures don't count). Each criterion is binary: yes or no.
If ALL eight criteria are negative (all answered 'No'), PERC is satisfied and PE is ruled out. No further testing (no D-dimer, no CT) is needed, and you can confidently explore alternative diagnoses. The false-negative rate is <2% in low-risk patients. If ANY single criterion is positive, PERC fails. This does NOT mean the patient has PE; it means PERC cannot rule it out. Proceed with standard workup: calculate [Wells PE Score](/tools/wells-pe-score), order D-dimer if Wells is low/moderate, and obtain CTPA if D-dimer is positive or Wells is high. For patients with leg swelling, also consider [Wells DVT Score](/tools/wells-dvt-score). Document your PERC assessment: 'PERC rule applied. All 8 criteria negative. PE ruled out. Exploring musculoskeletal/anxiety etiology.'
Emergency physicians
Apply PERC as the first step in chest pain or dyspnea evaluation when PE is in your differential but pre-test probability is low. PERC-negative patients (all 8 criteria negative) can be safely discharged without D-dimer or CT, avoiding the false-positive D-dimer cascade. This streamlines ED workflow, reduces radiation exposure, eliminates contrast risks, and prevents incidental findings that lead to unnecessary follow-up. In busy EDs, PERC can rule out PE in 20-30% of low-risk patients within minutes, freeing up CT resources for higher-risk cases and reducing observation time.
Urgent care providers, physician assistants
In urgent care settings where D-dimer or CT access may be limited or delayed, PERC provides a safe rule-out strategy for low-risk patients. A PERC-negative young patient with pleuritic chest pain after coughing can be diagnosed with musculoskeletal pain and discharged with NSAIDs, avoiding transfer to the ED. This is particularly valuable in rural or community settings where imaging resources are constrained. Always document pre-test probability and all eight PERC criteria clearly to support your decision if the patient re-presents.
Primary care physicians, family medicine
When a patient presents to your office with dyspnea and you're considering PE but think it's unlikely (more likely asthma exacerbation, anxiety, deconditioning), PERC helps you decide whether to send the patient to the ED for workup. A PERC-negative patient with a more plausible alternative diagnosis can be managed conservatively with close follow-up, avoiding unnecessary ED visits and costly testing. This is especially useful for anxious patients who have multiple ED visits for chest pain with negative workups — PERC provides objective reassurance.
Triage nurses, paramedics
Triage nurses can use PERC to identify very-low-risk patients early in the ED workflow. A young patient with chest pain, HR 85, SpO2 98%, no risk factors, and normal exam can be triaged as lower acuity, allowing focus on higher-risk patients. Some EDs incorporate PERC into triage protocols or electronic health record decision support to flag patients who may not need PE workup. This frontloads clinical decision-making and can reduce overall testing volumes.
Hospitalists, internal medicine
When consulted on a hospitalized patient with new dyspnea or chest pain, PERC helps decide whether PE workup is warranted. A post-operative patient (>4 weeks post-op) with pleuritic pain, low pre-test probability, and all PERC criteria negative can be evaluated for atelectasis, pneumonia, or musculoskeletal pain without reflexive D-dimer ordering. This reduces false-positive D-dimers in hospitalized patients (where D-dimer specificity is notoriously low) and prevents unnecessary anticoagulation exposure or CT utilization.
ED directors, quality officers
PERC is a high-value, low-cost intervention for reducing unnecessary diagnostic testing. Implementing PERC-based protocols can decrease D-dimer orders by 15-25% and CT utilization by 5-10% in ED chest pain populations without increasing missed PE rates. Track PERC utilization, test-ordering patterns, and PE miss rates as quality metrics. Educational interventions teaching appropriate PERC application (emphasizing the low pre-test probability requirement) improve adherence and safety. PERC aligns with Choosing Wisely recommendations to reduce low-value testing.
The single most common error with PERC is applying it to patients with moderate or high pre-test probability. PERC was validated ONLY in low-risk populations. If you're genuinely worried about PE, don't use PERC. Use clinical gestalt: 'Is PE my leading diagnosis or a close second?' If yes, skip PERC and go straight to Wells + D-dimer or imaging. If PE is far down your differential ('probably musculoskeletal but I should consider PE'), then PERC is appropriate. When in doubt, don't PERC.
If you're uncertain whether pre-test probability is low enough for PERC, calculate [Wells PE Score](/tools/wells-pe-score) first. Wells <2 corresponds to ~10% PE prevalence, which is appropriate for PERC. Some clinicians apply a two-step approach: Wells first, then PERC if Wells is low. This adds objectivity and defensibility to your assessment. However, PERC is fastest when applied immediately based on gestalt in obviously low-risk patients (young, no risk factors, clear alternative diagnosis).
The SpO2 criterion (<95%) ONLY applies to room air measurements. If the patient is on home oxygen or was placed on supplemental O2 in triage, you cannot use their current SpO2. Either check room air SpO2 (remove O2 briefly if safe) or count this criterion as positive (PERC fails). Many patients with COPD on home O2 will fail PERC on this criterion alone, and that's appropriate — chronic hypoxemia increases VTE risk.
The estrogen criterion captures oral contraceptive pills, hormone replacement therapy, pregnancy (physiologic estrogen elevation), and estrogen-containing transgender hormone therapy. Even low-dose OCPs count. If the patient took their last OCP dose <1 week ago (recently stopped), consider this positive. Don't forget to ask about estrogen use — patients may not volunteer it. Pregnancy is both a risk factor and complicates workup, so any pregnant patient fails PERC and warrants careful PE assessment.
The surgery criterion specifies procedures or trauma requiring hospitalization in the past 4 weeks. Outpatient procedures (colonoscopy, dental work, carpal tunnel release) do NOT count. The threshold is general anesthesia with admission or significant trauma with admission. This distinction matters: don't fail PERC for a patient who had outpatient knee arthroscopy 2 weeks ago. Document the type and timing of surgery if borderline.
Hemoptysis is defined broadly: any blood-streaked sputum, blood-tinged mucus, or frank blood. Even a single episode counts. It doesn't have to be massive. If the patient coughed up blood once this morning, the criterion is positive. Hemoptysis is rare in PE (~10% prevalence), but when present it raises concern significantly. Don't dismiss trace hemoptysis as 'just from coughing' — it fails PERC and warrants workup.
Medicolegal safety requires clear documentation. Write: 'Pre-test probability for PE is low based on [age, lack of risk factors, alternative diagnosis]. PERC rule applied. All 8 criteria negative. PE ruled out per PERC. No further testing indicated. Diagnosis: [musculoskeletal chest pain / anxiety / viral pleurisy].' This demonstrates systematic evaluation and provides a defensible rationale if the patient re-presents. If PERC fails, document which criterion was positive and your next step (Wells, D-dimer, etc.).
Studies show that PERC safely reduces D-dimer ordering by 20-30% in low-risk ED chest pain populations without increasing PE miss rates. The benefit is greatest in young, healthy patients with musculoskeletal or anxiety-related chest pain. In older populations with more comorbidities, PERC fails more often (due to age ≥50, tachycardia, etc.), so the impact is smaller. Target PERC use in low-risk demographics where it will have the most impact.
Unlike [Wells PE Score](/tools/wells-pe-score) (which is a score), PERC is binary: pass or fail. You don't 'score' how many PERC criteria are positive. One positive criterion has the same meaning as five positive criteria: PERC cannot rule out PE. Don't try to risk-stratify based on the number of PERC positives. If PERC fails, proceed to Wells Score for formal risk stratification, then D-dimer or imaging based on Wells category.
PERC does not explicitly include active malignancy, recent long-distance travel, obesity, thrombophilia, or smoking. A patient with metastatic cancer and dyspnea may technically be PERC-negative but still warrants PE workup due to high cancer-associated VTE risk. Use clinical judgment: if the patient has major risk factors not captured by PERC, don't rely on PERC alone — proceed with Wells Score and further testing. PERC is a tool to support clinical judgment, not replace it.
The PERC rule is a binary pass/fail assessment. If all eight criteria are negative (answered 'No'), the PERC rule is satisfied, and pulmonary embolism can be considered ruled out without further testing in the appropriate clinical context. The false-negative rate in this scenario is less than 2%, which falls below the accepted testing threshold for PE.
If any single criterion is positive (answered 'Yes'), the PERC rule fails, and PE cannot be excluded by clinical assessment alone. This does not mean the patient has PE; it means further workup is needed, typically starting with a D-dimer test. If the D-dimer is also elevated, CT pulmonary angiography is generally indicated.
It is critical to understand that PERC is only valid when the clinician's pre-test probability is already low (less than 15% by clinical gestalt or Wells Score). Applying PERC to moderate- or high-risk patients will lead to missed diagnoses.
Apply the PERC rule in the emergency department when evaluating a patient with chest pain, dyspnea, or other symptoms that raise the question of pulmonary embolism, but your clinical assessment (gestalt or Wells Score) suggests the pre-test probability is low. The purpose is to determine whether you can safely avoid ordering a D-dimer, thereby preventing the cascade of false-positive D-dimers leading to unnecessary CT pulmonary angiography.
PERC is specifically designed for the low-risk population where the clinician has already considered PE in the differential but believes it is unlikely. It should not be used as a first-line screening tool or applied to patients in whom PE is a serious concern.
The most important limitation of the PERC rule is that it must only be applied to patients with a low pre-test probability of PE. Using it in moderate- or high-risk patients will result in missed diagnoses. The clinician must first establish that pre-test probability is low before applying the eight criteria.
The PERC rule was validated primarily in US emergency department populations and may not perform identically in other healthcare settings or populations with different PE prevalence. Some studies have shown slightly higher false-negative rates in certain subgroups, including hospitalized patients and those with active malignancy.
PERC does not replace clinical judgment. Even if all criteria are negative, a clinician with strong suspicion for PE based on the overall clinical picture should proceed with further testing. The rule is a decision support tool, not an absolute directive.
For related assessments, see Wells Score (PE) and Wells Score (DVT).
Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.
Calculate the Wells Score to estimate the clinical probability of pulmonary embolism (PE). Guide decisions on CTPA and D-dimer testing.
EmergencyCalculate the Wells Score to assess the clinical probability of deep vein thrombosis (DVT). Guide diagnostic workup and D-dimer testing.
Only apply PERC when clinical pre-test probability is LOW (<15%).