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Calculators · Venous thromboembolism

PERC — Pulmonary Embolism Rule-out Criteria

The PERC rule is not a probability score: it is a filter. In patients in whom the clinical suspicion of pulmonary embolism is already very low, a negative result on all eight criteria brings the residual probability below 2% and makes it possible to skip even the D-dimer test, avoiding the cascade of investigations triggered by false positives.

Interactive tool

Apply the eight criteria

Tick each criterion that is met (that is, “PERC negative” for that item). The rule can only be applied if you have already estimated a low clinical probability: without this precondition the result is not valid.

How to use it

Instructions

Mandatory precondition

Apply PERC only after estimating a low clinical probability

The rule was derived and validated in patients with a pre-test probability < 15% on overall clinical judgement (gestalt), or with Wells < 2 / low-risk Geneva. Applying it to a patient with intermediate or high probability is a methodological error that can lead to a missed diagnosis: in those populations PERC is not safe enough.

The eight criteria

Every criterion must be met. A single unmet criterion is enough for the rule to be positive, and D-dimer testing must then follow.

  1. Age < 50 years.
  2. Heart rate < 100 bpm (highest value recorded in the emergency department, not just the current one).
  3. SpO2 ≥ 95% on room air.
  4. No haemoptysis.
  5. No current oestrogen use: oral contraceptives, patches or rings, hormone replacement therapy, high-dose oestrogens.
  6. No previous DVT or pulmonary embolism.
  7. No unilateral leg swelling (clinically evident calf asymmetry).
  8. No surgery or trauma requiring hospitalisation or general anaesthesia in the past 4 weeks.

Practical interpretation

  • All 8 criteria met (PERC negative) → pulmonary embolism ruled out: no D-dimer, no CT angiography. The residual risk at 45 days is < 2%, lower than the risk of complications from the tests avoided.
  • Even one criterion not met (PERC positive) → the rule rules nothing out: proceed with D-dimer according to the usual algorithm. Note: a positive PERC does not mean the patient has a pulmonary embolism, only that the filter has not worked.

Clinical references

Guidelines and interpretation

Origin and validation

The rule was derived by Kline JA. and colleagues (J Thromb Haemost 2004) in more than 3000 patients and prospectively validated in a multicentre cohort of 8138 patients (Kline JA. et al., J Thromb Haemost 2008), with a sensitivity of 97.4% and a 45-day thromboembolic event rate of 1.0% in PERC-negative patients who underwent no further investigation.

The randomised non-inferiority trial PROPER (Freund Y. et al., JAMA 2018), conducted in 14 French emergency departments, compared the PERC strategy with the conventional strategy in low-probability patients: the difference in the 3-month thromboembolic event rate was 0.1% (within the non-inferiority margin), with a significant reduction in CT angiography and length of stay in the emergency department.

What the guidelines say

  • ESC 2019: the PERC rule may be considered in outpatients or emergency department patients with low clinical probability to rule out pulmonary embolism (class IIb, level B).
  • ASH 2018: in patients with low pre-test probability, PERC is suggested as a first step rather than direct D-dimer testing (conditional recommendation, very low certainty of evidence).
  • ACEP: PERC is recommended as a tool to limit D-dimer use in the very-low-risk emergency department population.

Populations in which PERC should not be used

SituationReason
Intermediate or high clinical probabilityThe rule has not been validated: the residual risk exceeds the safety threshold
Pregnancy and the postpartum periodDifferent prevalence and physiology; use the dedicated algorithms (adapted YEARS)
Patient already on anticoagulantsTreatment changes both the clinical picture and the D-dimer
Active cancer, known thrombophilia, strong family historyThe baseline probability is never truly “low”
Populations with a high prevalence of PE (> 20%)The negative predictive value of the rule falls below the acceptable threshold
Why avoiding unnecessary D-dimer matters

In low-probability patients, D-dimer is falsely positive in a substantial proportion of cases: the result is a CT angiogram with radiation exposure, contrast load, incidental findings and possible overdiagnosis of subsegmental emboli of uncertain clinical significance. PERC was designed to break this chain at its source.

References

Sources

  • Kline JA. et al., J Thromb Haemost 2004 — Clinical criteria to prevent unnecessary diagnostic testing in emergency department patients with suspected pulmonary embolism.
  • Kline JA. et al., J Thromb Haemost 2008 — Prospective multicenter evaluation of the pulmonary embolism rule-out criteria.
  • Freund Y. et al., JAMA 2018 — Effect of the Pulmonary Embolism Rule-Out Criteria on subsequent thromboembolic events among low-risk emergency department patients: the PROPER randomized clinical trial.
  • ESC 2019 — Guidelines for the diagnosis and management of acute pulmonary embolism.
Disclaimer

Quick-reference tool for healthcare professionals. It does not replace the original guidelines, the summaries of product characteristics or the specialist's clinical judgement. All calculations run in the browser: no patient data is transmitted to or stored on any server.

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