This PERC rule calculator is used to rule out patients that are already deemed to have a low risk of pulmonary embolism to allow searching a different diagnosis. You can read more about the pulmonary embolism ruling out criteria below the form.

Age equal or higher than 50

Heart rate higher than 100 bpm

O2 saturation on room air less than 95%

Prior History of DVT or VT


Trauma or surgery within last month

Unilateral leg swelling

Exogenous estrogen source

How does this PERC rule for pulmonary embolism calculator work?

This is a health tool that is designed to provide help in assessing cases that are suspicious of PE but in which the symptoms are likely to be cause by some other condition.

PERC = Pulmonary Embolism Rule-out Criteria and covers 8 clinical signs questions that should be answered with either yes or no and then the result will uncover whether the ruling out can be done or diagnosis should continue because there is not enough evidence to rule out pulmonary embolism.

PERC rule mnemonic

A very useful mnemonic to remember the PERC rule in practice is “HAD CLOTS

Hormone therapy – exogenous estrogen

Age equal or higher than 50

DVT PE history

Coughing blood – hemoptysis

Leg swelling – unilateral

O2 saturation on room air less than 95%

Tachycardia - heart rate higher than 100 bpm

Surgery - Trauma or surgery within last month

PERC Rule interpretation

PERC rule calculator is somehow the opposite of models such as the Geneva or Wells score that stratify the risk of PE, as in this case, the test tries to rule out PE to allow further differentiated diagnosis in patients that are already put in the low risk category by previous tests. Therefore if all criteria are deemed with a no answer, further tests for PE may not be needed anymore. However, if just one out of the seven questions is positive, the PERC rule is invalid and diagnosis needs to continue.

The PERC rule testing is considered to have a sensitivity of 97.4%, a specificity of 21.9% and a false negative rate of just 1% making it a valuable tool in preventing diagnostic tests to be used unnecessary, especially imagistic ones.

However, in cases where PERC rule cannot be validated, the first step is to do a D-dimer test. Following this, if the test is negative and clinical criteria are consistent towards low risk, differentiated diagnosis should be established. If the D-dimer test is positive however, then it should be done a CT angiography.


1) Kline JA, et al. Clinical criteria to prevent unnecessary diagnostic testing in emergency department patients with suspected pulmonary embolism. J Thromb Haemost 2004; 2: 1247–55.

2) Kline JA, et al. Prospective multicenter evaluation of the pulmonary embolism rule-out criteria. J Thromb Haemost 2008; 6: 772–80.

3) Wolf SJ, et al. Assessment of the pulmonary embolism rule-out criteria rule for evaluation of suspected pulmonary embolism in the emergency department. Am J Emerg Med. Feb 2008; 26(2): 181-185.

01 Jul, 2015