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Respiratory
PERC Rule
Pulmonary Embolism Rule-out Criteria — 8-item rule to exclude PE without testing.
When to use: Applied in patients with LOW pretest probability for PE. If ALL 8 criteria are negative (PERC negative), PE can be excluded without D-dimer or CT-PA. Do not apply if pretest probability is intermediate or high.
Calculator
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Formula
PERC Negative = ALL 8 criteria met:
Age <50, HR <100, SpO₂ ≥95%, No leg swelling, No haemoptysis,
No recent surgery, No prior VTE, No hormone use
Key Points for NEET PG
- PERC only valid when pretest probability is LOW (clinical gestalt or Wells PE score <2)
- PERC-negative has ~2% false-negative rate — acceptable threshold per guidelines
- D-dimer is sensitive but non-specific; PERC avoids D-dimer testing entirely in low-risk patients
- Wells PE score first classifies pretest probability; PERC applies only to low-probability group
- CT-PA is test of choice for PE diagnosis — PERC avoids unnecessary radiation in low-risk patients
References
Prospective multicenter evaluation of the pulmonary embolism rule-out criteria · Journal of Thrombosis and Haemostasis (2008)
For educational purposes only. Not for clinical decision-making without professional oversight.