PERC Rule For Pulmonary Embolism

Differentiates between patients at low or high risk of pulmonary embolism.

In the text below the calculator there is more information on the rule and on the original study.

The PERC rule reveals patients who are at low risk of pulmonary embolism in an accurate and rapid manner so differential diagnosis can be initiated.

It is most often used in the assessment of patients suspected of PE, when clinical data is more suggestive of another diagnosis.

PERC comes from Pulmonary Embolism Rule-out Criteria and consists of 8 clinical signs.

The PERC is validated if neither of the 8 signs is present. This means that PE diagnosis can be ruled out.

In case at least one of the signs is present, PE diagnosis should continue with D-dimer testing or CT pulmonary angiography.

The PERC testing is considered to have a sensitivity of 97.4%, a specificity of 21.9% and a false negative rate of just 1%.


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

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PERC rule explained

The Pulmonary Embolism Rule-out Criteria consists of 8 clinical signs of pulmonary embolism. It is used for the assessment of patients who are suspected of PE but are more likely to be suffering from a different condition.

The rule can determine whether diagnosis of PE should continue (with D-dimer testing followed by CT pulmonary angiography if necessary) or if PE can be safely ruled out and differential diagnosis should be applied.

The 8 clinical signs can be remembered in practice with the mnemonic “HAD CLOTS”:

■ Hormone therapy – exogenous estrogen;

■ Age equal or higher than 50;

■ DVT or VT 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.

If neither of the above is deemed positive, then pulmonary embolism diagnosis can be ruled out. If at least one of the above is present, then diagnosis must continue.

There are several clinical models that are addressed to patients suspected or already diagnosed with pulmonary embolism:

■ Geneva score and Wells criteria – predict risk of PE and help reduce unnecessary diagnosis investigations in low risk patients;

■ POMPE-C and PESI score – stratify 30-day mortality risk in patients diagnosed with PE, based on clinical data;


About the study

The PERC screening method was created in 2004 by Kline et al. following a derivation study, on 3,148 patients, aimed at reducing the use of D-dimer tests.

The eight criteria were derived from logistic regression analysis with stepwise backward elimination of 21 variables.

The rule was then prospectively tested in two groups:

■ A low-risk group (1,427 patients initially tested for PE with a D-dimer test);

■ A very low-risk group (382 patients complaining of dyspnea, PE not suspected).

The prevalence of PE was 8% in the low-risk group and 2% in the very low-risk group.

There is a 1.8% threshold that accounted for risks associated with PE diagnosis and treatment:

■ CT radiation;

■ Anaphylaxis from contrast;

■ Bleeding from anticoagulation.

The PERC rule has proven a sensitivity of 97.4%, a specificity of 21.9% and a false negative rate of just 1% (below the 1.8% threshold) and can help reduce unnecessary imagistic tests in patients at low risk of PE.


Original source

Kline JA, Mitchell AM, Kabrhel C, Richman PB, Courtney DM. Clinical criteria to prevent unnecessary diagnostic testing in emergency department patients with suspected pulmonary embolism. J Thromb Haemost 2004; 2: 1247–55.


Kline JA, Courtney DM, Kabrhel C, Moore CL, Smithline HA, Plewa MC, Richman PB, O'Neil BJ, Nordenholz K. Prospective multicenter evaluation of the pulmonary embolism rule-out criteria. J Thromb Haemost. 2008; 6(5):772-80.

Other references

1. 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.

2. Hugli O, Righini M, Le Gal G, Roy PM, Sanchez O, Verschuren F, Meyer G, Bounameaux H, Aujesky D. The pulmonary embolism rule-out criteria (PERC) rule does not safely exclude pulmonary embolism. J Thromb Haemost. 2011; 9(2):300-4.

3. Penaloza A, Verschuren F, Dambrine S, Zech F, Thys F, Roy PM. Performance of the Pulmonary Embolism Rule-out Criteria (the PERC rule) combined with low clinical probability in high prevalence population. Thromb Res. 2012; 129(5):e189-93.

Specialty: Pulmonology

System: Respiratory

Objective: Evaluation

Type: Rule

No. Of Criteria: 8

Year Of Study: 2004

Abbreviation: PERC

Article By: Denise Nedea

Published On: June 12, 2017

Last Checked: June 12, 2017

Next Review: June 12, 2023