title: High blood eosinophil count is a risk factor for future asthma exacerbations in adult persistent asthma.
abstract: 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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Departments of Allergy and Research and Evaluation, Kaiser Permanente Southern California, San Diego and Pasadena, Calif. Electronic address: robert.s.zeiger@kp.org.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Zeiger
authors.affiliation: Departments of Allergy and Research and Evaluation, Kaiser Permanente Southern California, San Diego and Pasadena, Calif.
authors.forename: Michael
authors.initials: M
authors.lastname: Schatz
authors.affiliation: Departments of Allergy and Research and Evaluation, Kaiser Permanente Southern California, San Diego and Pasadena, Calif.
authors.forename: Qiaowu
authors.initials: Q
authors.lastname: Li
authors.affiliation: Departments of Allergy and Research and Evaluation, Kaiser Permanente Southern California, San Diego and Pasadena, Calif.
authors.forename: Wansu
authors.initials: W
authors.lastname: Chen
authors.affiliation: MedImmune, Gaithersburg, Md.
authors.forename: Deepak B
authors.initials: DB
authors.lastname: Khatry
authors.affiliation: MedImmune, Gaithersburg, Md.
authors.forename: David
authors.initials: D
authors.lastname: Gossage
authors.affiliation: Observational Research Center, AstraZeneca, Gaithersburg, Md.
authors.forename: Trung N
authors.initials: TN
authors.lastname: Tran
mesh_terms: D000293:Adolescent; D000305:Adrenal Cortex Hormones / Q000627:therapeutic use; D058666:Adrenergic beta-2 Receptor Agonists / Q000627:therapeutic use; D000328:Adult; D000553:Ambulatory Care; D001249:Asthma / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology / Q000276:immunology / Q000628:therapy; D002140:California / Q000453:epidemiology; D016208:Databases, Factual; D018450:Disease Progression; D011307:Drug Prescriptions; D004636:Emergency Service, Hospital; D004802:Eosinophilia / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology / Q000276:immunology / Q000628:therapy; D004804:Eosinophils / Q000276:immunology*; D005260:Female; D006279:Health Maintenance Organizations; D006760:Hospitalization; D006801:Humans; D007958:Leukocyte Count; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011379:Prognosis; D012189:Retrospective Studies; D012307:Risk Factors; D013997:Time Factors; D055815:Young Adult
chemical_list: D000305:Adrenal Cortex Hormones; D058666:Adrenergic beta-2 Receptor Agonists
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