The Importance of Eosinophils in the Course of Diseases: Eosinopenia, COVID-19 and Mortality

INTRODUCTION: Eosinophils are involved in many metabolic events, such as the provision of homeostasis in the organism, host cell defense, and tissue repair and regeneration. Despite these important roles, eosinophils can be overlooked during the examination of blood tests performed in daily clinical practice. This study aimed to investigate the role of eosinophils in the clinical course of COVID-19.
METHODS: In this study, patients who presented to the emergency department with symptoms of COVID-19 and had a positive polymerase chain reaction test or typical COVID-19 involvement on thoracic computed tomography were evaluated retrospectively. The patients’ demographic data and blood parameters were obtained. In addition, the patients’ outcomes, requirements for admission to inpatient wards or the intensive care unit, mechanical ventilation requirements, and in-hospital mortality were recorded and statistically analyzed.
RESULTS: The study included a total of 3,845 patients. The eosinophil count was found to be lower in cases requiring hospitalization, intensive care, or mechanical ventilation, and in those with in-hospital mortality. In addition, the eosinophil count was found to be the most significant prognostic factor among all investigated parameters.
DISCUSSION AND CONCLUSION: Although eosinophil count is often overlooked, it is one of the factors that determines the prognosis in critically ill patients, as in the case of COVID-19. To the best of our knowledge, this is the first study to investigate the effect of eosinophil count on the course of COVID-19 and compare the utility of eosinophil count with other complete blood count parameters for this purpose.