A simple tool to help ruling-out Covid-19 in the emergency department: derivation and validation of the LDH-CRP-Lymphocyte (LCL) score

Abstract

After the outbreak of the Covid-19 pandemic, cases of SARSCoV- 2 infections may gradually decrease in the next months. Given the reduced prevalence of the disease, Emergency Departments (ED) are starting to receive more and more non- Covid19 patients. Thus, a way to quickly discriminate ED patients with potential Covid-19 infection from non-Covid19 patients is needed in order to keep potentially contagious patients isolated while awaiting second-level testing. In this paper, we present the derivation and validation of a simple, practical, and cheap score that could be helpful to rule out Covid-19 among ED patients with suspicious symptoms (fever and/or dyspnoea). The LCL score was derived from a cohort of 335 patients coming to the ED of our hospital from March 16th to April 1st, 2020. It was then retrospectively validated in a similar cohort of 173 patients admitted to our ED during April. The score is based on blood values of lactate dehydrogenase, C-reactive protein, and lymphocyte count. The LCL score performed well both in the derivation and in the validation cohort, with an AUC respectively of 0.81 (95% CI: 0.77 – 0.86) and of 0.71 (95% CI: 0.63 – 0.78), given the difference in Covid- 19 prevalence between the two cohorts (57% vs 41% respectively). An LCL score equal to 0 had a negative predictive value of 0.92 in the derivation cohort and of 0.81 in the validation cohort, with a negative likelihood ratio respectively of 0.08 and 0.36 for Covid- 19 exclusion. This score could, therefore, constitute a useful tool to help physicians manage patients in the ED.

The CoLab-score rapidly and efficiently excludes COVID-19 at the emergency department without need for SARS-CoV-2 testing: a multicenter case-control study

“…The main strength of this study is that the CoLab-score can be used as a means of early-warning or triaging tool for the entire ED population, regardless of presenting symptoms. This is in contrast to the vast majority of COVID-19 diagnostic models that have been developed on a sub-population of PCRtested patients (Brinati et al, 2020;Fink et al, 2020;Giamello et al, 2020;Joshi et al, 2020;Kurstjens et al, 2020;Plante et al, 2020;Qin et al, 2020;Tordjman et al, 2020). Moreover, the CoLab-score requires only routine blood tests instead of (features from) imaging such as CT-scans or one or more laboratory test results that are not routinely measured in the ED such as interleukin-6 or 3hydroxybuteric acid (Wynants et al, 2020).…”

“…In the era of algorithms and artificial intelligence, it is very appealing to develop predictive or diagnostic tools based on information readily available. In fact, models have been developed to identify SARS-CoV-2-positive patients (Brinati et al, 2020; Fink et al, 2020; Giamello et al, 2020; Joshi et al, 2020; Kurstjens et al, 2020; Plante et al, 2020; Qin et al, 2020; Tordjman et al, 2020), to describe the severity of COVID-19 symptoms or to predict deterioration or ultimately admission at the intensive care unit (Linssen et al, 2020; Wang et al, 2020; Zeng et al, 2021; Zhou et al, 2020). For an extensive overview and critical appraisal of models developed for COVID-19 we refer to the living systematic review by Wynants et.…”

Development and validation of an early warning score to identify COVID-19 in the emergency department based on routine laboratory tests: a multicentre case–control study

“…The main strength of this study is that this score can be used as an early warning or triaging tool for the ED population presenting with abdominal pain, chest pain, shortness of breath, syncope, sepsis or other non-specific complaints where a routine blood panel is requested. This is in contrast to the vast majority of COVID-19 diagnostic models that have been developed on a preselected population of PCR-tested patients 9 21–27. Moreover, the CoLab-score requires only routine blood tests, instead of (features from) imaging such as CT scans or laboratory tests that are not routinely collected in the ED, for example, interleukin 6 or 3-hydroxybutyric acid 4.…”