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Use PERC “with confidence” to rule-out pulmonary embolism

Reuters Health • The Doctor's Channel Daily Newscast

“The rule has shown consistent performance in different settings. Hence, it can be used with confidence,” Dr. Subhash Chandra, who was involved in the analysis, told Reuters Health.PERC also has “acceptable” specificity for ruling out pulmonary embolism in patients with low pretest probability, the authors note in a report online in Annals of Emergency Medicine.

PERC, commonly used in patients arriving at the emergency department with possible pulmonary embolism, includes eight parameters readily available at initial presentation: age younger than 50, pulse rate above 100 beats/min, SpO2 > 94%, no unilateral leg swelling, no hemoptysis, no surgery or trauma within four weeks, no previous deep venous thrombosis or pulmonary embolism, and no oral hormone use.

Patients meeting all eight criteria are believed to have a pretest probability low enough to defer D-dimer testing.

In 2010, a systematic review and meta-analysis of clinical decision rules for pulmonary embolism was published but it didn’t include PERC, which prompted the current analysis by Dr. Chandra’s team.

Through an exhaustive literature search, they found 12 qualifying studies from six countries that evaluated PERC in a total of 13,885 patients (1,391 pulmonary embolism diagnoses). Ten studies were prospective in design and 2 were retrospective.

In the pooled analysis, PERC had a sensitivity of 0.97; specificity of 0.23; positive likelihood ratio of 1.24; and negative likelihood ratio of 0.17.

There was “consistent high sensitivity and negative predictive value of PERC, with missed pulmonary embolism in just 0.5% of patients,” Dr. Chandra and colleagues report.  The major limitation of PERC is its low but acceptable specificity,” they note.

“Low specificity is acceptable for a clinical decision rule, which can easily be calculated based on initial assessment; (it’s) not time or resource demanding,” Dr. Chandra commented.

“Use of PERC can safely still exclude about 20% of patients for need for d-dimer and further expensive testing without increasing risk of missing pulmonary embolism,” Dr. Chandra said.

Dr. Inge Mos, from the Section of Vascular Medicine, Leiden University Medical Center, the Netherlands, who was not involved in the study, but reviewed it for Reuters Health, said he didn’t see any “surprises” in the data.

“The pooled sensitivity of this study was slightly lower compared to other clinical decision rules but with overlapping confidence intervals. Also, a lower specificity of 23% vs around 30% with other clinical decision rules,” Dr. Mos said.

Dr. Mos noted, however, that “previous studies have shown that a clinical decision rule alone is not reliable enough to confirm or exclude pulmonary embolism.”


Diagnostic Accuracy of Pulmonary Embolism Rule-Out Criteria: A Systematic Review and Meta-analysis

Ann Emerg Med. 2011. Published online December 19, 2011.