PERC Rule Calculator
Rule out pulmonary embolism without further testing using the PERC clinical criteria. Enter values for instant results with step-by-step formulas.
Reviewed by Rahul Singh, Health & Wellness Specialist
Formula
PERC Rule: All 8 criteria must be ABSENT to rule out PE
The PERC rule is a binary decision tool. If all eight criteria are negative in a patient with low pre-test probability for PE, further workup is unnecessary. Even a single positive criterion means the rule is not satisfied and additional testing is recommended.
Worked Examples
Example 1: Low-Risk Patient - PERC Negative
Problem:A 35-year-old woman presents with pleuritic chest pain. No tachycardia, no leg swelling, no hemoptysis, no recent surgery, no prior DVT/PE, no hormone use, SpO2 98%. Low pre-test probability by clinical gestalt.
Solution:Age >= 50: No\nHR >= 100: No\nImmobilization/surgery: No\nPrior DVT/PE: No\nHemoptysis: No\nRecent surgery/trauma: No\nUnilateral leg swelling: No\nHormone use: No\nPositive criteria: 0 of 8
Result:PERC NEGATIVE - All criteria absent. No further PE workup needed. Miss rate < 1.8%.
Example 2: Low-Risk Patient - PERC Positive
Problem:A 55-year-old man with chest pain and shortness of breath. HR 88, SpO2 97%, no leg swelling, no hemoptysis, no surgery, no prior DVT/PE, no hormones. Low pre-test probability.
Solution:Age >= 50: Yes (age 55)\nHR >= 100: No\nImmobilization/surgery: No\nPrior DVT/PE: No\nHemoptysis: No\nRecent surgery/trauma: No\nUnilateral leg swelling: No\nHormone use: No\nPositive criteria: 1 of 8
Result:PERC POSITIVE - 1 criterion met. Proceed with D-dimer testing. If D-dimer negative, PE excluded.
Frequently Asked Questions
What is the PERC rule and when should it be used?
The PERC (Pulmonary Embolism Rule-out Criteria) rule is a clinical decision tool designed to identify patients at very low risk for pulmonary embolism who do not need further diagnostic testing. It was developed by Dr. Jeffrey Kline and validated in a large multicenter study published in 2004. The rule should only be applied to patients who already have a low clinical pre-test probability for PE, typically less than 15 percent. It consists of eight clinical criteria, and if all eight are negative, the clinician can safely exclude PE without ordering a D-dimer test or CT angiography.
What are the eight PERC criteria?
The eight PERC criteria are age 50 years or older, heart rate of 100 beats per minute or higher, oxygen saturation on room air less than 95 percent, unilateral leg swelling, hemoptysis (coughing up blood), recent surgery or trauma within the past four weeks, prior history of DVT or PE, and hormone use including oral contraceptives or hormone replacement therapy. Each criterion is assessed as either present or absent. The key feature of the PERC rule is that all eight criteria must be absent to rule out PE, making it an all-or-nothing assessment tool.
How accurate is the PERC rule at ruling out PE?
When applied correctly to low pre-test probability patients, the PERC rule has a sensitivity of approximately 97.4 percent and a negative predictive value exceeding 99 percent. The miss rate when all eight criteria are negative is less than 1.8 percent, which falls below the accepted testing threshold of 1.8 percent for PE. A large multicenter validation study involving over 8,000 patients confirmed these results. However, accuracy drops significantly if the rule is applied to patients with moderate or high pre-test probability, which is why proper patient selection is essential before applying this tool.
When should the PERC rule NOT be used?
The PERC rule should not be applied to patients with moderate or high clinical suspicion for pulmonary embolism, as it was only validated for low pre-test probability populations. It is inappropriate for hemodynamically unstable patients, those with clear signs of massive PE, or patients in whom another diagnosis has not already been considered. The rule should also not be used in patients who are already on anticoagulation therapy or those with known thrombophilia conditions. Emergency physicians should first determine the pre-test probability using clinical gestalt or a validated score like the Wells criteria before deciding whether PERC is applicable.
References
Reviewed by Rahul Singh, Health & Wellness Specialist · Editorial policy