Peripheral eosinophil count as a biomarker for asthma exacerbation severity in acute care settings.

Background: Eosinophilic asthma is associated with frequent exacerbations, but the relevance of peripheral eosinophil count at the time of exacerbation is unknown.

Objective: To evaluate peripheral eosinophil count during an exacerbation requiring health care utilization and its associations with exacerbation course in adults with asthma.

Methods: Adult asthma exacerbations between 2016 and 2023 which resulted in an emergency department visit or hospitalization were identified by International Classification of Diseases, 10th Revision, Clinical Modification diagnosis codes in the Johns Hopkins Asthma Precision Medicine Center of Excellence data repository. Outcomes included probability of admission, maximal level of care, length of stay, and discharge rate. We estimated associations between outcomes and eosinophil count using generalized estimating equations and generalized linear models.

Results: Among 11,178 asthma exacerbations, 63% had peripheral eosinophil count measured during the encounter before steroid administration, and eosinophilia (≥150 cells/µL) was present in 61% of these. Risk of admission was nonlinearly associated with eosinophil count; exacerbations with eosinophil count of 150 to 300 cells/µL at presentation were least likely to result in admission, whereas those with 30 (odds ratio: 1.39, 95% CI: 1.26-1.54, P < .001) or 1000 cells/µL (odds ratio: 1.55, 95% CI: 1.35-1.79, P < .001) had higher odds of admission. Among inpatient exacerbations (N = 3825), encounters with eosinophil count more than or equal to 300 cells/µL had shorter median length of stay (3.1 vs 2.4 days, P < .001) and higher discharge rate (hazard ratio: 1.34, 95% CI: 1.22-1.48, P < .001) than those without eosinophilia (<150 cells/µL).

Conclusion: Peripheral eosinophil count is a biomarker for asthma exacerbation severity and duration, offering opportunities for improved assessment and management of asthma exacerbations in acute care settings.