Emergencies
Pulmonology
Vascular medicine
The PERC rule is designed for a specific situation: a patient in whom the clinician already considers the pre-test probability of pulmonary embolism to be low. When all eight criteria are negative, it can help avoid additional testing as part of a validated algorithm. It must not be applied to an intermediate- or high-risk patient.
Number of questions
8 criteria
Approximate duration
≈ 1 minute
Population
Adults with suspected low clinical probability pulmonary embolism
Modality
clinical rule
QuestionnairePERC
CLINICIAN SCORE
The patient must meet all of the following conditions at the same time. Only to be used in patients whose pre-test probability of pulmonary embolism is already deemed low.
Are you patient?
PERC is not a test for the general public: it is only relevant after an initial clinical probability assessment by a healthcare professional.
Terms of contract
The PERC rule only applies after a prior clinical assessment has deemed the probability of pulmonary embolism to be low (less than 15% according to NICE), with other plausible diagnoses considered. Oxygen saturation must be measured on room air and all eight criteria must be completed; an unknown criterion cannot be assumed negative. The surgery/trauma criterion applies to the past four weeks requiring hospitalisation. PERC is only used following a low prior clinical assessment; it is not a general screening tool.
Score interpretationPERC
Each unfulfilled condition counts as a positive criterion (1 point). Total of 0 to 8 positive criteria.
Total score
First reading
0
to
0
8 negative criteria + low prior clinical probability: negative PERC.
1
to
8
At least 1 positive criterion: positive PERC.
0 positive criteria (8 negative criteria) with low pre-test clinical probability: PERC negative; at least 1 positive criterion: PERC positive.
Off-label use increases the risk of false reassurance. Oxygen saturation, medical history, and pre-test risk assessment must be properly established.
Frequently asked questions
Is PERC a score?
Does a negative PERC rule out a PE every time?
What are its limitations?
Sources and references
Kline JA et al.
Kline JA et al., J Thromb Haemost, 2004
In practice
Full name
Pulmonary Embolism Rule-out Criteria
Method
clinical rule
Language
Not applicable (clinical score)
Authors
Kline JA et al.
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