Performance of the Pulmonary Embolism Rule-out Criteria (the PERC rule) combined with low clinical probability in high prevalence population

Abstract

Introduction

PERC rule was created to rule out pulmonary embolism (PE) without further exams, with residual PE risk < 2%. Its safety is currently not confirmed in high PE prevalence populations even when combined with low clinical probability assessed by revised Geneva score (RGS). As PERC rule and RGS are 2 similar explicit rules with many redundant criteria, we hypothesized that the combination of PERC rule with gestalt clinical probability could resolve this limitation.

Methods

We collected prospectively documented clinical gestalt assessments and retrospectively calculated PERC rules and RGS from a prospective study of PE suspected patients. We analyzed performance of combinations of negative PERC with low clinical probability assessed by both methods in high overall PE prevalence population.

Results

Among the final study population (n = 959), the overall PE prevalence was 29.8%. Seventy-four patients (7.7%) were classified as PERC negative and among them, 4 patients (5.4%) had final diagnosis of PE. When negative PERC was combined with low pretest probability assessed by RGS or gestalt assessment, PE prevalence was respectively 6.2% and 0%. This last combination reaches threshold target of 2% and unnecessary exams could easily have been avoided in this subgroup (6%). However, it confidence interval was still wide (0%; CI 0–5).

Conclusions

PERC rule combined with low gestalt probability seems to identify a group of patients for whom PE could easily be ruled out without additional test.

A larger study is needed to confirm this result and to ensure safety.

Introduction

Because its clinical signs and symptoms are nonspecific and very common, acute pulmonary embolism (PE) is a real diagnostic challenge for clinicians. The fear of missing a potentially mortal diagnosis, associated with the wide availability and relatively low cost of the D-dimer test, has resulted in increasing testing for PE. However, the poor specificity of the D-dimer test leads to an elevated rate of false positive results. This could involve an overall increase of further exams negative for PE, with potentially harmful consequences for patients (radiation exposure, contrast iodine injection…), cost-effectiveness imbalance and increased patient length of stay in overcrowded emergency departments (ED) [1], [2]. Moreover, unnecessary exams may lead to incidental findings which not only cause anxiety among patients but also prompt serial follow-up imaging studies [3].

In order to decrease the number of unnecessary exams, Kline et al. [4] derived and validated a PE exclusion rule (the PERC rule) (Table 1). If all 8 criteria are negative, patients are identified as PERC negative (PERC (−)) and should not require further testing, even D-dimer, because the residual PE risk in this group is lower than equipoise. Equipoise represents the threshold where the probability that the patient will be harmed by further exams exceeds the probability that the patient will benefit from further testing [5]. This threshold was estimated by Kline et al. at 2% [4], [6], a similar rate to the one of thromboembolic event recurrences after negative angiogram (1.7%; 95% confidence interval (CI) 1–2.7) [7]. The PERC rule was subsequently evaluated in several studies [6], [8], [9], [10], [11], [12]. Concordant results were obtained by most of them [6], [9], [10], [11] but results were not conclusive when the PERC rule was applied to European populations with high overall PE prevalence (more than 20%). Righini et al. applied the PERC rule alone and found 6.7% of false negatives, suggesting that the PERC rule should be used in combination with another clinical assessment rule in order to identify a very low risk PE population [8]. Hugli et al applied the PERC rule combined with low pretest probability using the revised Geneva score. In this selected population, they observed that prevalence of PE remained unacceptably high (6.4%) [12]. We hypothesized that this negative result may be due to the fact that the PERC rule and the revised Geneva score are two similar explicit rules with many redundant criteria, and that the combination of the PERC rule with an empirical assessment of clinical probability (clinician gestalt) could resolve this limitation. We therefore compared the PERC rule combined with low clinical probability assessed by the revised Geneva score or the clinician gestalt in a non-selected European population with high overall prevalence of PE.