Eosinophilia and Risk of Thrombosis and Mortality in Hospitalized Patients: A Retrospective Cohort Study

Background: Eosinophilia, defined as peripheral blood eosinophil counts > 0.5 K/μL, is associated with various clinical conditions, including allergic, infectious, and malignant diseases. Emerging evidence suggests that eosinophils may contribute to thrombo-inflammatory processes, but their association with thromboembolic events and mortality remains insufficiently characterized. This study aimed to evaluate whether eosinophilia is independently associated with increased risk of thromboembolic events and mortality in hospitalized patients. Methods: We conducted a retrospective cohort study using electronic medical records from Sheba Medical Center (2011–2020). Eosinophilia was classified as mild (0.5–1.5 K/μL) or hypereosinophilia (HE, >1.5 K/μL). Patients with eosinophilia were matched 1:1 to controls with normal eosinophil counts based on age, sex, and follow-up duration. Results: Among 93,320 patients (46,660 with eosinophilia and 46,660 controls), thromboembolic events occurred in 20.9% of eosinophilic patients vs. 9.8% of controls. Eosinophilia was independently associated with thrombosis (OR = 1.33; 95% CI, 1.28–1.38; p < 0.0001), with increased risk from counts ≥ 0.7 K/μL. Mortality was also higher among eosinophilic patients (HR = 1.17; 95% CI, 1.13–1.20; p < 0.0001). Conclusions: Eosinophilia is associated with increased thromboembolic and mortality risk, highlighting the importance of eosinophil monitoring in clinical practice.