Article Citation: Kline JA, et al. “Prospective multicenter evaluation of the pulmonary embolism rule-out criteria”. J Thromb Haemost. 2008. 6(5):772-780.

What we already know about the topic: PERC (Pulmonary Embolism Rule-out Criteria): Age > = 50 years, Pulse >= 100, SpO2 <= 95% on RA, Unilateral leg swelling, Hemoptysis, Surgery or trauma < = 4 weeks ago requiring treatment with general anesthesia, Prior PE or DVT, Hormone use.

PERC rule has better sensitivity than Wells criteria for ruling out PE.

Why this study is important: low risk patients are exposed to increased radiation exposure from CTA and it can be prevented using clinical gestalt and the PERC rule.  CTs have carcinogenic properties and a validated clinical decision rule can give physicians the confidence to avoid a CTA chest.  And we know that CTs can also be falsely positive and cause adverse outcomes.

Brief overview of the study: multi-center, prospective, cohort study that included 12 EDs in the US and 1 in New Zealand.  It enrolled 8138 patients with suspected PE from 2003-2006.  The emergency department physicians documented the presence or absence of each PERC factor, with their degree of suspicion about the presence of a PE prior to any testing.  Workup was then performed on all of these patients and outcomes were followed over the next 45 days.  The PERC rule had high sensitivity for ruling out PE.  1666/8138 patients were considered low risk for PE and were PERC-negative and only 15 (1%) had a PE with 1 death.   When combining low pretest probability and PERC-negative, the sensitivity is 97.4%.

Limitations: prospective non-interventional trial, low prevalence of PE in this study population (5.9% in 45 days), clinical gestalt is required to determine pre-test probability.

Take home points: if a patient is determined low risk for PE by clinical gestalt and is PERC negative, the probability of venous thromboembolism and all-cause mortality at 45 days is reduced to below 2%.