PE Testing in PERC Negative Patients

Written by Alex Chen

25% of patients who were Pulmonary Embolism Rule-Out Criteria (PERC) negative underwent testing for PE. Among those tested, there was a low yield (1.6%) for PE, which is similar to the initial PERC study.

Why does this matter?
We are scanning more people for PE, and we are subsequently diagnosing more segmental and subsegmental PEs. While you could say that we should be happy about “missing fewer” PEs, there is controversy regarding whether these are clinically significant. In addition to the resources and radiation, there is great potential harm in putting someone on anti-coagulation. We should be utilizing the tools available to us (such as PERC) to help us make decisions about whether we should subject our patients to further testing.

Perks of using PERC?
This was a prospective study which enrolled a convenience sample of 3024 patients from a single academic ED center with chief complaints of chest pain and/or shortness of breath within the last 24 hours. A PERC score was calculated for all patients. A Well’s score was calculated for all PERC negative patients. They utilized a dichotomized cutoff of <4.5 to define low risk and excluded 5 patients who were PERC negative but moderate-risk by Well’s. Interestingly, a recent paper by Kline outlined a framework on how to apply PERC which utilized a Well’s score of <2 as low-risk criteria. The primary outcome of this study was PE testing in PERC (-) patients, which was defined as D-dimer, CTPA, or V/Q. 

A total of 17.5% of the patients were PERC (-). Interestingly, 25.5% of PERC (-) patients underwent PE testing compared to 35.4% of PERC (+) patients; 7.2% of PERC (-) patients went to scan without a D-dimer. Among the PERC (-) patients who underwent testing, 2 patients (1.6%) tested positive for PE. This is precisely what would have been predicted with the original PERC study from Kline, which had a false-negative rate of 1% (95%CI 0.6 - 1.6%). While it is named the PE Rule-out Criteria, it isn’t meant to be a zero-miss rule.

The authors were surprised to find that there were so many patients that were PERC (-) who were being tested anyway. They postulated a number of factors, such as changes in vitals from triage to differences in asking questions and performing the physical exam. A more likely reason seems to be other factors that increased the clinician’s pre-test probability of PE and fell outside of PERC and Well’s criteria such as pleuritic chest pain (OR 1.74) or family history of VTE (OR 1.51). As a side note, syncope had an OR of 0.94 but was not significant.

Pulmonary Embolism Testing among Emergency Department Patients who are Pulmonary Embolism Rule-out Criteria Negative. Acad Emerg Med. 2017 Aug 8. doi: 10.1111/acem.13270. [Epub ahead of print]

Another Spoonful

Peer reviewed by Thomas Davis, MD.