key: cord-0850638-ep9cogzb
authors: Ehrman, Robert R; Collins, Jonathan; Harrison, Nicholas
title: Prevalence of Pulmonary Embolism in ED patients with Suspected COVID‐19: The Truth Remains Unknown
date: 2020-09-23
journal: Acad Emerg Med
DOI: 10.1111/acem.14137
sha: 8106038767717a287e39143092555a7b5eeb83f2
doc_id: 850638
cord_uid: ep9cogzb

A strong association between PE and patients hospitalized with COVID‐19 (15.3% overall range 0‐35%) has been reported, but the prevalence in ED patients remains unknown. The contribution of traditional risk factors is likewise unclear. While Freund et al. attempted to answer to this question, we have methodologic concerns we feel require attention before emergency physicians proceed as if COVID‐19 does not increase risk of PE.

contribution of traditional risk factors is likewise unclear 2 . While Freund et al. 3 attempted to answer to this question, we have methodologic concerns we feel require attention before emergency physicians proceed as if COVID-19 does not increase risk of PE.

First, attempting to establish disease prevalence when only those tested for disease are included can lead to erroneous estimates of prevalence, an epidemiological pitfall known as the "referral filter" 4 . Prevalence may be over or underestimated, depending on the similarity between the tested and non-tested groups. No data about patient volume or characteristics are provided by Freund et al. for the non-tested group, and thus readers cannot understand the potential impact of selection bias-a critical limitation preventing application of these data to other populations 5 . The referral filter tends to suppress missed cases of disease 6 , so the rate of PE observed in this retrospective study may simply relate to the type of patients in whom CTPAs were ordered. The pandemic nature of COVID-19 may have deterred minimally symptomatic patients from visiting the ED, potentially inflating PE prevalence. Alternatively,

given the rise in out-of-hospital cardiac arrest in COVID-19 hotspots 7 , patients with PE and COVID-19 may have died before seeking care, thereby decreasing PE prevalence. Furthermore, Accepted Article knowledge of CTPA usage and PE prevalence in non-pandemic time periods would be useful as significant differences from the study period would suggest additional confounding.

Second, the study period encompasses the early pandemic, when little was known about the disease and diagnostic and treatment strategies changed rapidly. The authors adjust for this by including a "week" variable in their regression model. While they report no effect therefrom, data for weekly PE incidence is not presented, the effect size the study would have power to detect in terms of per-week PE incidence is not discussed, and no attempt is made to control for the number of patients "at risk" during the study period (e.g., CTPAs/1000 visits).

Taken together, we believe that these factors preclude exclusion of study week as a potential confounder and that changes in diagnostic approach likely influenced reported PE prevalence.

Despite the authors' statements to the contrary, at least 9 papers exploring COVID-19associated coagulopathy and increased thrombotic burden were published before the study period concluded [8] [9] [10] [11] [12] [13] [14] [15] [16] . Therefore we suspect that increased awareness of COVID-19-associated coagulopathy lead to greater use of CTPA and thus a biased estimate of PE prevalence in this study.

Freund et al. have undertaken a task of great import, as determination of the association of PE and COVID-19 in ED patients affects diagnostic and therapeutic interventions.

While the study has a litany of strengths, we feel there are key limitations in recruitment and analysis that cast substantial doubt on the finding of equal PE prevalence between groups. As such, we believe that prudence requires continued consideration of COVID-19 as risk factor for PE until a methodologically rigorous epidemiological study can be performed.

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Deep Vein Thrombosis and Pulmonary Embolism: Two Complications of COVID-19 Pneumonia?

Accepted Article This article is protected by copyright. All rights reserved 12

Anticoagulant treatment is associated with decreased mortality in severe coronavirus disease 2019 patients with coagulopathy

Abnormal coagulation parameters are associated with poor prognosis in patients with novel coronavirus pneumonia

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