Severe Asthma and Blood Eosinophils: A Retrospective Cohort Analysis using Electronic Health Records

Thought Leadership  |  29 August 2019  |  By John M. Farah, PhD


Asthma, a complex respiratory disease characterized by airway inflammation, airflow limitation, and bronchial hyper-responsiveness, is estimated to affect 25 million Americans. The clinical burden and economic costs of asthma are substantial and correlate closely with disease severity. Approximately 5% to 10% of patients have severe asthma that remains uncontrolled or is only partially controlled despite adherence to standard treatment. Severe uncontrolled asthma varies among patients with respect to presentation, treatment response, and clinical outcomes. Characterizing patients according to observable traits (phenotype) and pathobiologic mechanisms (endotype) has the potential to personalize asthma management through a biomarker-driven approach that enables accurate diagnosis and effective use of standard and targeted therapies.

This paper reviews the management and pharmacologic treatment of severe asthma and describes eosinophilic asthma, a subtype associated with frequent exacerbations of symptoms and poor prognosis that accounts for up to one-half of severe cases. Next, we consider how real-world observations may offer insight into the challenges and opportunities associated with uncontrolled asthma. Using de-identified ambulatory patient data sourced from Practice Fusion a Veradigm™ EHR to generate actionable real-world evidence, we characterized patients who required additional therapy for control of asthma symptoms and evaluated how blood eosinophil levels affected personalization of asthma care. More than one-half of patients had evidence of persistent severe asthma. Asthma Control Test™ scores suggested asthma was not well controlled for a substantial proportion of patients completing the test. Over 25% of patients had blood eosinophil counts greater than or equal to a threshold associated with increased healthcare utilization and disease burden that may identify patients who are likely to benefit from therapies targeting type 2 inflammation. The retrospective analysis suggests opportunities exist for consideration of biologics for patients in whom eosinophils play a pathobiologic role. Studies that leverage real-world data from electronic health platforms may inform innovative therapeutics and provide insight into eosinophilic asthma, other subtypes of severe asthma, and treatment effectiveness in support of care plans tailored to individual patients.

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