Eosinopenia <100/μL as a marker of active COVID-19: An observational prospective study

Abstract

Objectives: To analyse the diagnostic performance of eosinopenia, alone or combined with polymorphonuclear neutrophils (PMN) and/or lymphocytes, as a marker of active COVID-19 in patients hospitalized for suspicion of SARS-CoV-2 infection.

Methods: A prospective observational study including patients hospitalized for suspicion of COVID-19 in a COVID unit was performed from 20th March to 5th April 2020, in Perpignan, France. Patients for which there was a doubt upon diagnosis, who were recently under oral corticosteroids, had myeloid malignancy or human immunodeficient virus infection were excluded. SARS-CoV-2 detection was performed using an RT-PCR assay, from nasopharyngeal swab specimens. Complete blood count were performed for all patients.

Results: One-hundred and twenty-one patient were included: 57 patients were diagnosed with COVID-19, 64 patients were not. Eosinophil count was lower in the COVID-19 group (median: 0/μL versus 70/μL, p < 0.0001). To diagnose COVID-19, eosinopenia had a sensitivity of 89.5% and a specificity of 78.1% while lymphopenia's were 73.7% and 62.5% respectively. Using area under curve (AUC) of receiving operating characteristics (ROC) curves, eosinophil's optimal cut-off level was 10/μL, sensitivity and specificity were 86%, and 79.7% respectively. Regarding the eosinophil/PMN ratio, the optimal cut-off level was 3.344, sensitivity and specificity were 87.7% and 73.4% respectively. The AUC of lymphocyte/PMN ratio was significantly lower than eosinophil/PMN ratio's (0.621 versus 0.846, p = 0.0003).

Conclusion: Eosinopenia - <10/μL - and eosinophil/PMN ratio are useful, low-cost, reproducible tools to help diagnose COVID-19, during an epidemic period, in a population of hospitalized patients admitted for suspicion of COVID-19.

Keywords: COVID-19; Eosinopenia; Marker; SARS-CoV-2.

Figure 1

Flowchart of the study population at admission

Figure 2

Receiver-operating characteristics (ROC) curves in the total cohort for various biomarker cutoff levels. Areas under the ROC curves: CRP, 0.759 (95% confidence interval (CI), 0.671–0.846); Eo, 0.852 (95% CI, 0.784–0.920); Ly (95% CI, 0.667–0.842); Eo/PMN ratio × 1000, 0.846 (95% CI, 0.778–0.914); Ly/PMN ratio × 1000, 0.621 (95% CI, 0.521–0.721). Statistical difference between areas under the ROC curves of Eo and Ly counts using Delong's method: p-value=0.0845. Statistical difference between areas under the ROC curves of Eo/PMN ratio × 1000 and Ly/PMN ratio × 1000 using Delong's method: p-value=0.0003. CRP: C-reactive protein; Eo: eosinophil; Ly: lymphocyte; PMN: polymorphonuclear neutrophil.