Elevated Blood Eosinophil Levels Are a Risk Factor for Asthma Exacerbations

Released: 12-May-2014 11:00 AM EDT
Embargo expired: 20-May-2014 11:15 AM EDT
Source Newsroom: American Thoracic Society (ATS)
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Citations 2014 American Thoracic Society International Conference

Newswise — ATS 2014, SAN DIEGO ─ In adults with persistent asthma, elevated blood eosinophil levels may be able to predict which individuals are at increased risk for exacerbations, according to a new study presented at the 2014 American Thoracic Society International Conference.

“Eosinophils are known to be involved in the pathophysiology of asthma, and determining their relationship with asthma exacerbations may allow us to determine in advance which of these patients needs targeted interventions,” said lead author Dr. Robert Zeiger, MD, PhD, Physician Investigator at Kaiser Permanente in San Diego, California. “In our study, elevated blood eosinophil levels were found to be a risk factor for subsequent exacerbations in adult asthma patients.”

Eosinophils are white blood cells that become active in individuals with certain allergic diseases, including asthma, and other medical conditions.

In the study, blood eosinophil levels were measured in 2,392 adult asthma patients in 2010 and the relationship between these levels and the rate of exacerbations in 2011 was determined in analyses adjusting for demographics, co-morbidities, and asthma burden and care.
Increasing level of blood eosinophil at baseline was associated with increasing risk of future asthma exacerbation in both crude and adjusted analyses. The relationship was observed in crude analysis for baseline eosinophil level of >300/mm3 (crude rate ratio 1.25; 95% CI, 1.04-1.51, P = 0.02) and was weaker after adjustment for baseline characteristics (adjusted rate ratio 1.16; 95% CI, 0.97-1.39, P=0.11). A baseline eosinophil level of >400/mm3 was associated with future asthma exacerbations in 2011 after adjustment for baseline features (adjusted rate ratio 1.31; 95% CI, 1.07-1.60, P<0.01).
Other factors in 2010 that were significantly associated with an increased risk of exacerbations in 2011 included a history of prior asthma exacerbations, GINA steps-4/5 care, dispensing of 7 or more short-acting beta-agonist canisters, female gender, black ethnicity, and obesity.
“Our findings suggest that asthma patients with an elevated blood eosinophil level have a greater disease burden,” said Dr. Zeiger. “If our findings can be replicated in other populations and settings, measurement of blood eosinophil levels may help guide treatment for patients at the greatest risk for exacerbations.”
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* Please note that numbers in this release may differ slightly from those in the abstract. Many of these investigations are ongoing; the release represents the most up-to-date data available at press time.

Abstract 50175
Elevated Blood Eosinophil Level Is A Risk Factor For Exacerbations In Adult Persistent Asthma
Type: Scientific Abstract
Category: 01.09 - Asthma Mediators (AII)
Authors: R.S. Zeiger1, M. Schatz1, Q. Li2, W. Chen2, D. Khatry3, T.N. Tran3; 1Kaiser Permanente Southern California - San Diego, CA/US, 2Kaiser Permanente Southern California - Pasadena, CA/US, 3MedImmune, LLC - Gaithersburg, MD/US

Abstract Body
Rationale: Exacerbation associated uncontrolled allergic asthma represents a major public health problem. In addition, the eosinophil contributes to asthma pathophysiology as an allergic inflammatory mediator. Ascertaining the relationship of elevated blood eosinophil level and exacerbation risk in a large Managed Care Organization should help further identify patients who require specific asthma care management.
Methods: Using administrative pharmacy and health care utilization data collected in the KPSC research data warehouse, we identified 2,392 asthma patients between ages 18-64 years who met the Heath Effectiveness Data and Information Set administrative criteria for persistent asthma in both 2009 and 2010, did not evidence other major illnesses including chronic obstructive lung disease, and had a blood eosinophil determination (distribution by cut-points, Table) in 2010. Exacerbations were defined as asthma emergency department visits/hospitalizations or asthma outpatient visits requiring systemic corticosteroid dispensing within +7 days. A period of at least 8 days defined a new exacerbation. Multivariate Poisson regression was used to examine the association between blood eosinophil level determined in 2010 and rate of exacerbation in 2011 adjusting for demographics, asthma burden and care, and co-morbidities.
Results: The cohort was majority female (70.4%), ethnic minority (52.0%), more than high-school educated (81.9%), and obese (53.3%) with long-term health plan membership (median 14.8 years) and infrequently current smokers (6.5%). At baseline, step-care treatment level based on Global Initiative for Asthma definitions were 24%, 32%, and 44% for steps-1/2, step-3, and steps-4/5 respectively. Rate of asthma exacerbations in 2011 was 0.41 event per person-year (95% confidence interval (CI), 0.37-0.45) and increased significantly with higher baseline step-care level (P<0.01). A cut-point of >400/mm3 related best to future asthma exacerbation risk. Elevated eosinophil level >400/mm3 at baseline was independently associated with asthma exacerbations in 2011 after adjustment for multiple baseline features (Adjusted Rate Ratio, 1.31; 95% CI, 1.07-1.60, P<0.01) . Other factors in 2010 that were significantly associated with increased rate of exacerbations in 2011 were: history of prior asthma exacerbations (P<0.01), steps-4/5 care (P<0.01), female gender (P<0.01), >7 short-acting beta-agonist (SABA) canister-dispensing (P<0.01), Black ethnicity (P=0.01), and obesity (P=0.02).
Conclusions: Elevated blood eosinophil level was an independent risk factor for future asthma exacerbations in adults with persistent asthma suggesting a higher disease burden in asthma patients with elevated blood eosinophil. More studies are needed to confirm this finding in different populations and settings.


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