PERC rules safely exclude PE in low risk patients(PROPER Trial)

Yonathan Freund, Marine Cachanado et el published in JAMA the results of PROPER trial which evaluated safety of PERC criteria in low risk patients at ruling out pulmonary embolism.


PERC criteria were first suggested by Kline JA , Mitchell AM et el in 2004.  They include the following 

  1. Arterial oxygen saturation (SpO2) of 94%or less,
  2. Pulse rate of at least 100/min,
  3. Patient age of 50 years or older,
  4. Unilateral leg swelling,
  5. Hemoptysis,
  6. Recent trauma or surgery,
  7. Prior PE or deep venous thrombosis (DVT),
  8. Exogenous estrogen use

A PERC score of zero safely excludes PE in ED patients with a low probability without further testing.

These were subsequently validated in several cohort studies.  However, study by Hugli, showed that PERC had an unacceptably high 6% to 7% failure (ie, false-negative) rate. PERC rules  were never tested in any randomized clinical trial.


This was a non-inferiority, crossover cluster–randomized clinical trial aimed at assessing the safety of the PERC-based strategy to test the hypothesis that the diagnosis of PE can be safely excluded among ED patients with a low
clinical probability and a PERC score of zero without further diagnostic testing.


14 Emergency departments in France.


In the intervention group, the diagnostic work-up included an initial calculation of the PERC score. If the PERC score was zero, PE was ruled out without subsequent testing. If the PERC score was positive, the usual diagnostic strategy was applied.

In the control group, the diagnostic work-up for PE followed the usual diagnostic strategy—after inclusion and classification as low gestalt probability, D-dimer testing was recommended for all patients, followed (if D-dimer–positive) by a CTPA.

All patients were observed for 3 months. Based on recent large European cohorts, it was estimated that the rate of primary endpoint in control group will be 1.5%, and to prove a non inferiority , 1624 subjects were needed in control group.


The primary end point was the occurrence of a symptomatic thromboembolic event during the 3-month follow-up period, which was not diagnosed at the time of the inclusion visit.

The primary end point was adjudicated in 1749 patients (per-protocol with follow-up population)—902 in the control group and 847 in the PERC group.

A PE was diagnosed at the initial visit in 40 (2%) patients overall, 14 (1.5%) in the PERC group vs 26 (2.7%) in the control group (difference, 1.3%[95%CI, −0.1%to 2.7%]; P= 0.052.

The only missed pulmonary embolism or failure of the PERC rule to identify a PE that occurred in this study was that of a young male with chest pain and no previous medical history. He was PERC-negative and initially discharged but then seen again the next day with ongoing pain. When he presented the second time, a D-dimer was checked and found to be positive followed by a CTPA, interpreted as inconclusive, with radiological signs consistent with  pneumonia. The patient was admitted, had lower-limb Doppler ultrasonography that showed no VTE and then a V/Q scan showed sub segmental defects.

Patients in the PERC group were significantly less frequently investigated by CTPA (129 [13%]) vs 220 (23%) in the control group (difference, 9.7% [95% CI, 6.1% to 13.2%).

Secondary results

There was no significant difference in the rate of all-cause mortality at 3 months (0.3% [3 patients] in the PERC group vs 0.2% [2 patients] in the control group [difference, 0.1% {95% CI, −0.5% to 0.7%}]; P > .99), in 3-month hospital readmission rates (4% [43 patients] in the PERC group vs 7% [62 patients] in the control group; P = .051), and there was no severe hemorrhage or severe adverse events subsequent to CTPA (0 in both groups).


Trial protocol may have allowed PERC-negative patients(No D dimer or CTPA) with PE mild enough to not result in a subsequent visit to a health care professional to receive testing for PE, thereby missing the true negatives. Prevalance of PE in the patients was very low and failure rate of diagnosis strategy in the control group was also very low.  There was no patient level randomization.  54 patients were lost to follow up.


PERC criteria can be safely used to rule out PE in low risk patients presenting to Emergency room. This may be specially useful in developing countries where facility to have testing such as CTPA is scarcely available.

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