PERC Calculator: Pulmonary Embolism Rule-Out Criteria

Your details

Patient is aged 50 years or above. The original PERC validation used a cut-off of 50, not 65.
Any tachycardia on the presenting ECG or vital signs. Note: beta-blockers may mask tachycardia.
Pulse-oximetry below 95% while breathing ambient air. This criterion cannot be applied if supplemental oxygen is running.
Asymmetric swelling of one leg suggestive of deep vein thrombosis. Full-leg swelling, not just ankle oedema.
Any blood-tinged sputum or frank blood coughed up, however small the volume.
Any surgical procedure requiring general or regional anaesthesia, or significant traumatic injury, in the 4 weeks before presentation.
Confirmed prior pulmonary embolism or deep vein thrombosis at any point in the patient's history.
Oral contraceptive pills, hormone replacement therapy, or any other form of exogenous estrogen or progestogen.
PERC ScorePERC-Negative (Rule-Out)
0criteria met

Number of positive PERC criteria (0 to 8)

InterpretationPERC-negative: all 8 criteria absent. In a patient with pre-test probability below 15%, PE can be safely excluded without further testing.
Recommended next stepNo D-dimer or imaging required. Reassess if clinical picture changes or pre-test probability is not genuinely low.
0 criteria
PERC-Negative<1Low Positive1-3High Positive3+

PERC-negative: PE may be safely excluded in a pre-test low-risk patient.

  • All 8 PERC criteria are absent. In patients already assessed as low risk (pre-test probability below 15%), this result supports safe discharge without D-dimer testing.
  • Studies show the missed PE rate for PERC-negative, low-risk patients is below 2%, comparable to the rate of false-positive D-dimers causing unnecessary CT scans.
  • PERC-negative status does not apply if the patient has any moderate or high pre-test probability by Wells score or clinical gestalt.

Next stepConfirm the pre-test probability is below 15% by clinical gestalt or Wells score before applying the rule-out. If the patient deteriorates, reassess immediately.

 = Powered by OnlyCalculators