EBQ:PERC Rule Validation

Complete Journal Club Article

Kline J.A. et al. "Prospective multicenter evaluation of the pulmonary embolism rule-out criteria". Journal of Thrombosis and Haemostasis. 2008. 6(5):772–780.
PubMed Full text PDF

Clinical Question

Can risk stratification to low risk for pulmonary embolism (PE) in combination with a negative Pulmonary Embolism Rule Out Criteria (PERC) score reduce the probability of PE to less than 2%?

Conclusion

The combination of gestalt estimate of low suspicion for PE and PERC(-) reduces the probability of VTE to below 2% in about 20% of outpatients with suspected PE.

Major Points

• This multicenter validation confirmed that the PERC rule can safely exclude PE without further testing in low-risk patients
• Among patients with gestalt-estimated low clinical probability and negative PERC, the false-negative rate was 1.0% (below the 2% testing threshold)
• Approximately 20% of patients evaluated for possible PE can be classified as PERC-negative and low clinical probability
• Application of the PERC rule in low-risk patients could significantly reduce unnecessary D-dimer testing and CT pulmonary angiography
• The study reinforced that PERC should only be applied when the pretest probability of PE is already judged to be low (<15%)

Overview

PERC Rule:

1. Age ≥ 50
2. HR ≥ 100
3. O2 Sat < 95% on room air?
4. Is there a present history of hemoptysis?
5. Is the patient taking exogenous estrogen?
6. Does the patient have a prior diagnosis of venous thromboembolism (VTE)?
7. Has the patient had recent surgery or trauma? (Requiring endotracheal intubation or hospitalization in the previous 4 weeks.)
8. Does the patient have unilateral leg swelling? (Visual observation of asymmetry of the calves.)

The rule estimates the risk of PE at < 2%.

Design

This was a prospective, non-interventional, multicenter study of patients presenting to the emergency department (ED) in 12 hospitals in the USA and one in Christchurch, New Zealand. Investigators were trained in applying the PERC Rule

Population Studied

8138 patients from 12,213 eligible patients

Inclusion Criteria

Inclusion was triggered by an order for a test to establish objective evidence of a PE, written by or under the supervision of a board-certified emergency physician. The decision to order this test was based upon information obtained from the initial history and physical examination, and medical records immediately available in the ED. Objective Evidence included:

1. Pulmonary vascular imaging study (CT angiography or VQ scan)
2. D-dimer assay ordered to evaluate for possible PE

tests to simply exclude a deep venous thromboembolsm did not trigger patient enrollment

Exclusion Criteria

1. Knowledge of a diagnostic positive pulmonary vascular imaging study performed within the previous 7 days.
2. The patient indicated that the enrollment hospital was not his or her hospital system of choice for follow-up.
3. Any circumstance that suggested that the patient would be lost to follow-up

.

Baseline Characteristics

• Average age: 49 years old
• Sex: 67% Female
• Symptoms: Dyspnea (51%) > Pleuritic CP (44%) > Substernal CP (34%) > Cough (29%) > Syncope (6%) > Hemptysis (3%)
• Comorbid Conditions: Current smoker (35%) > Immobility (25%) > Active malignancy (15%) > Known CAD (13%) > Prior PE/DVT & estrogen use (11%) > Pregnant/Post-partum (10%)

Interventions

• 72-field, web-based date form completed at the time of test order, which included gestalt pretest probability. Outcomes of image-proven VTE or death from any cause was followed on all enrolled patients at 45 days.

Outcomes

8138 patients tested, of which 513 were diagnosed with VTE at the index visit followed by another 47 patients after discharge. Thus, 561 patients (6.9%) were VTE (+). Of the total patients tested, 51% underwent CTA, 12% underwent venous ultrasound, and 6% underwent V/Q scan.

Primary Outcomes

• 1952 (24%) patients were PERC (-) with a sensitivity of 95.7% (95% CI 93.6-97.2%), a specificity of 25.4% (95% CI 24.4-26.4%), and a negative LR of 0.17 (95% CI 0.11-0.25%).
• 1666 (20%) patients were classified as very low risk with a sensitivity of 97.4% (95% CI 95.8-95.5%), a specificity of 21.9% (95% CI 21.0–22.9%), and a negative LR of 0.12 (95% CI 0.07–0.19%).

Criticisms

The PERC rule was derived in 2004 with the following criteria. Clinicians should use the rule if the pre-test probability is ≤15% for PE. If any of the following are positive then the risk of PE cannot be estimated to be <2% and further workup is needed.

PERC Rule:

1. Age ≥ 50
2. HR ≥ 100
3. O2 Sat < 95% on room air?
4. Is there a present history of hemoptysis?
5. Is the patient taking exogenous estrogen?
6. Does the patient have a prior diagnosis of venous thromboembolism (VTE)?
7. Has the patient had recent surgery or trauma? (Requiring endotracheal intubation or hospitalization in the previous 4 weeks.)
8. Does the patient have unilateral leg swelling? (Visual observation of asymmetry of the calves.)

Funding

Supported by Grants from the National Institutes of Health R41HL074415 and R42HL074415, K23HL077404 and R01 HL074384, and a Medical Student Award from the Emergency Medicine Foundation

Review Questions

1 PERC stands for pulmonary embolism rule out criteria. In this study of 8138 patients, 1666 were found to be low clinical suspicion and PERC negative. The conclusion of the study was

	patients with a medium probablity of PE and PERC negative can be discharged home
	patients with a high probability of PE and PERC positive should be anticoagulated
	patients with low probability of PE and PERC negative will have a probability of less than 2% of VTE
	PERC failed to be predictive of PE in this cohort of patients

2 PERC consists of the following rules:

	Age < 50, HR < 100, O2 sat >95%, No history of DVT/PE, No recent trauma or surgery, no hemoptysis, no exogenous estrogen, no unilateral leg swelling
	Age < 65, HR < 100, O2 sat >95%, No history of DVT/PE, No recent trauma or surgery, no hemoptysis, no exogenous estrogen, no unilateral leg swelling
	Age < 50, HR < 100, O2 sat >90%, No history of DVT/PE, No recent trauma or surgery, no hemoptysis, no exogenous estrogen, no unilateral leg swelling
	Age < 50, HR < 60, O2 sat >95%, No history of DVT/PE, No recent trauma or surgery, no hemoptysis, no exogenous estrogen, no unilateral leg swelling

3 The utility of the PERC rule is greatest in which of the following patients suspected of a pulmonary embolism?

	High pretest probability
	Intermediate pretest probability
	Low pretest probability

Related Publications

• ACEP clinical policy; Ann Emerg Med 2011; 57:628-650.

Further Reading

• 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
• Radecki, R. The PERC Rule Mini-Review. Emergency Medicine Literature of Note. August 23, 2011. Available at: http://www.emlitofnote.com/2011/08/perc-rule-mini-review.html