When should the PERC rule be applied?

PERC should ONLY be applied when the clinician's pretest probability for PE is already low (< 15%) based on gestalt. It is NOT a screening tool for all patients with chest pain or dyspnea. If pretest probability is moderate or high, skip PERC and proceed directly to D-dimer or CT angiography.

What happens if a patient fails the PERC rule?

If any one PERC criterion is positive, the patient "fails" PERC and should undergo D-dimer testing. An elevated D-dimer (≥ 500 ng/mL, or age-adjusted: age × 10 ng/mL for patients > 50) warrants CT pulmonary angiography. A negative D-dimer in a low-risk patient effectively rules out PE.

How does PERC fit into the PE diagnostic algorithm?

Step 1: Assess clinical probability (gestalt or Wells score). Step 2: If low probability, apply PERC — if all 8 criteria negative, PE is ruled out. Step 3: If PERC fails, check D-dimer. Step 4: If D-dimer positive, obtain CTPA. This approach safely reduces unnecessary imaging.

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PERC Rule

Rule out pulmonary embolism without D-dimer testing in low pretest probability patients. All 8 criteria must be negative (answered "No").

PERC Criteria

Answer "Yes" if the criterion is present. All must be "No" to PERC-out PE.

Age ≥ 50 HR ≥ 100 bpm SpO₂ < 95% on room air Unilateral leg swelling Hemoptysis Recent surgery or trauma (≤ 4 weeks) Prior PE or DVT Oral hormone use (estrogen/OCP)

PERC Negative

No criteria present — PE can be ruled out if pretest probability is low (< 15%).

PE Ruled Out (if low pretest)

⚠️ Important: The PERC rule should ONLY be applied when the clinician's gestalt pretest probability for PE is already low (< 15%). It is NOT a standalone screening tool and should not replace clinical assessment.

Disclaimer: For educational purposes only. Not a substitute for clinical judgment.

When to use

Apply PERC when your clinical gestalt suggests low pretest probability for PE (< 15%) and you want to avoid unnecessary D-dimer testing. If all 8 criteria are absent, PE probability falls below the test threshold (~1.8%), and further workup is unnecessary.

Clinical pearls

PERC is a rule-OUT tool only — it cannot rule IN PE.
Do NOT apply PERC to moderate or high pretest probability patients — proceed directly to D-dimer or imaging.
If any single PERC criterion is positive, proceed to D-dimer testing.
The PERC rule reduces unnecessary D-dimer testing, CT pulmonary angiography, radiation exposure, and incidental findings in low-risk patients.

References

Kline JA, 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.
Freund Y, et al. Effect of the Pulmonary Embolism Rule-Out Criteria on subsequent thromboembolic events (PROPER). JAMA. 2018;319(6):559-566.

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About This Tool

What Is the PERC Rule?

The Pulmonary Embolism Rule-out Criteria (PERC) is an 8-item clinical decision rule designed to identify patients in whom pulmonary embolism can be safely excluded without any further testing — including D-dimer. Developed by Kline et al. in 2004 and validated in the landmark PROPER trial (JAMA, 2018), PERC is based on the principle that in patients with already-low clinical suspicion for PE, the risks of further testing (false positives leading to unnecessary CT angiography, anticoagulation, radiation, and contrast exposure) may exceed the risk of a missed PE.

How It Works

The PERC rule assesses eight binary criteria: age ≥ 50, heart rate ≥ 100, SpO₂ < 95%, unilateral leg swelling, hemoptysis, recent surgery or trauma within 4 weeks, prior PE or DVT, and oral hormone use. If ALL eight criteria are absent in a patient with low clinical pretest probability (< 15%), PE is effectively ruled out with a miss rate below the testing threshold (~1.8%). Even a single positive criterion means the patient is NOT PERC-negative and should proceed to D-dimer or further workup.

Evidence and Integration into Practice

The PROPER trial (Freund et al., JAMA 2018) was a multicenter, randomized noninferiority study that validated the PERC strategy in European emergency departments. It showed that applying PERC in low-risk patients reduced diagnostic testing without increasing the rate of thromboembolic events at 3-month follow-up. PERC is now incorporated into major emergency medicine guidelines, including ACEP's Clinical Policy on PE (2018), as the first step in the PE diagnostic algorithm for low-risk patients. It significantly reduces healthcare resource utilization when applied correctly.

🔑 Clinical Pearls

PERC is only valid when your clinical gestalt (pretest probability) is already low (< 15%). Never apply it to moderate or high-risk patients.
The PERC rule was designed to reduce unnecessary D-dimer testing — if PERC-positive, proceed to D-dimer, not directly to CT-PA.
A single positive PERC criterion does NOT mean the patient has PE — it means further testing (D-dimer) is indicated.
PERC is particularly valuable in young, otherwise healthy patients with atypical chest pain and low clinical suspicion.

Key References

Kline JA, 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.
Freund Y, et al. Effect of the Pulmonary Embolism Rule-Out Criteria on subsequent thromboembolic events (PROPER). JAMA. 2018;319(6):559-566.
Wolf SJ, et al. Clinical policy: critical issues in the evaluation and management of adult patients presenting to the ED with suspected PE. Ann Emerg Med. 2018;71(1):e1-e42.

Formula last verified: February 2026