Eosinopenia and COVID-19.

Context: Early diagnosis of coronavirus disease 2019 (COVID-19) and patient isolation are important for both individual patient care and disease containment. The diagnosis is confirmed by testing for the presence of nasopharyngeal viral RNA with a polymerase chain reaction assay, which has limited availability, variable turnaround time, and a high false-negative rate. The authors report that a rapid laboratory test, the eosinophil count, readily obtained from a routine complete blood cell count (CBC), may provide actionable clinical information to aid in the early recognition of COVID-19 in patients, as well as provide prognostic information.

Objective: To investigate the diagnostic and prognostic value of eosinopenia in COVID-19-positive patients.

Methods: The eosinophil results of routine CBC from the first 50 admitted COVID-19-positive patients were compared with the eosinophil results of 50 patients with confirmed influenza infection at the time of presentation to the emergency department at Coney Island Hospital in Brooklyn, New York. The number of patients with 0 eosinophils on the day of presentation was also compared between the 2 groups. Furthermore, the eosinophil counts in the 50 COVID-19 patients were reviewed for the first 5 days of their hospital stay and before discharge, along with the outcome (deceased vs discharged), and trends in eosinophil data were compared based on the outcome.

Results: On the day of presentation, 30 patients in the COVID-19 group (60%) and 8 patients in the influenza group (16%) had an eosinophil count of 0. An additional 14 patients in the COVID-19 group had 0 eosinophils during the following 2 days; the total number of patients in the COVID-19 group who had 0 eosinophils on admission or during the ensuing 2 days was 44 (88%). In addition, 18 of 21 deceased patients in the COVID-19 group (86%) who initially presented with eosinopenia remained eosinopenic compared with 13 of 26 survivors (50%).

Conclusion: The absence of an eosinophil count in a CBC can aid in early diagnosis of COVID-19. It may be a useful tool in deciding whether to promptly isolate a patient and initiate specific therapies while waiting for confirmatory test results. Persistent eosinopenia after admission correlated with high disease severity and low rates of recovery.