High blood eosinophil count is a risk factor for future asthma exacerbations in adult persistent asthma

J Allergy Clin Immunol Pract. Nov-Dec 2014;2(6):741-50. doi: 10.1016/j.jaip.2014.06.005. Epub 2014 Aug 29.


Background: Exacerbation-associated uncontrolled asthma represents a major public health problem. The relationship of elevated blood eosinophils to this process needs study.

Objective: To determine whether a high blood eosinophil count is a risk factor for future asthma exacerbations in adult persistent asthma.

Methods: By using electronic pharmacy and health care data from Kaiser Permanente Southern California, 2392 patients, ages 18 to 64 years, were identified who met the Health Effectiveness Data and Information Set 2-year criteria for persistent asthma, did not manifest chronic obstructive pulmonary disease and other major illnesses, and had a blood eosinophil determination in 2010. Exacerbations (primary outcome) were defined as asthma outpatient visits that required systemic corticosteroid dispensing within ±7 days or asthma emergency department visits or hospitalizations. A period of ≥8 days defined a new exacerbation. Multivariate modelling used negative binomial and Poisson regression to examine the association between a blood eosinophil count determined in 2010 and risk of exacerbations, and ≥7 short-acting β2-agonist (SABA) canisters dispensed (secondary outcome) in 2011 by adjusting for demographics, comorbidities, and asthma burden.

Results: The rate of asthma exacerbations in 2011 was 0.41 events per person year (95% CI, 0.37-0.45). Eosinophil count ≥400/mm(3) in 2010 was a risk factor for asthma exacerbations in 2011 (adjusted rate ratio 1.31 [95% CI, 1.07-1.60]; P = .009) and ≥7 SABA dispensed (adjusted risk ratio 1.17 [95% CI, 1.03-1.1.33]; P = .015).

Conclusion: A high blood eosinophil count is a risk factor for increased future asthma exacerbations and excessive short-acting β2-agonist use after adjustment of potential confounders in adults with persistent asthma, which suggests a higher disease burden in patients with asthma and with high blood eosinophil counts.

Keywords: Administrative data; Allergist; Antiasthmatic agents; Asthma control; Eosinophils; Exacerbations; Impairment; Inhaled corticosteroids; Managed care organization; Oral corticosteroids; Outcome assessment (health care); Persistent asthma; Risk; Short-acting β(2)-agonists.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adrenal Cortex Hormones / therapeutic use
  • Adrenergic beta-2 Receptor Agonists / therapeutic use
  • Adult
  • Ambulatory Care
  • Asthma / blood
  • Asthma / diagnosis*
  • Asthma / epidemiology
  • Asthma / immunology
  • Asthma / therapy
  • California / epidemiology
  • Databases, Factual
  • Disease Progression
  • Drug Prescriptions
  • Emergency Service, Hospital
  • Eosinophilia / blood
  • Eosinophilia / diagnosis*
  • Eosinophilia / epidemiology
  • Eosinophilia / immunology
  • Eosinophilia / therapy
  • Eosinophils / immunology*
  • Female
  • Health Maintenance Organizations
  • Hospitalization
  • Humans
  • Leukocyte Count*
  • Male
  • Middle Aged
  • Predictive Value of Tests
  • Prognosis
  • Retrospective Studies
  • Risk Factors
  • Time Factors
  • Young Adult


  • Adrenal Cortex Hormones
  • Adrenergic beta-2 Receptor Agonists