Original ArticlesAsthma, Lower Airway DiseasesHigh blood eosinophil count is associated with more frequent asthma attacks in asthma patients
Introduction
Asthma is characterized by variable airflow obstruction, airway hyper-responsiveness, and chronic airway inflammation. Inflammation in asthma exhibits different phenotypes that can be characterized by the persistence at varying degrees of eosinophilic and neutrophilic infiltrations.[1], [2], [3] Eosinophilic asthma has been categorized based on larger numbers of eosinophils in bronchoalveolar lavage, airway tissue biopsies, or induced sputum in patients with clinical asthmatic symptoms and airway hyper-responsiveness.4
Knowledge of the epidemiology and disease burden of eosinophilic vs noneosinophilic asthma is still accumulating. Although noneosinophilic asthma can be severe and can present a significant burden,5 the clinical importance of eosinophils in asthma has been shown by the observation of frequent exacerbations of the disease in patients with sputum eosinophil counts higher than 3%.[6], [7] Clinical asthma studies of inhaled anti-inflammatory therapy designed to maintain sputum eosinophils below 2% or 3% have resulted in fewer exacerbations of the disease.[8], [9] Patients with refractory asthma with a recalcitrant high sputum eosinophil count on standard therapy also have shown improvement after therapy with anti–interleukin-5 monoclonal antibody that lowers airway and blood eosinophils.[10], [11], [12]
It is evident that a complete blood cell count can be performed at substantially lower cost and with greater accessibility than induced sputum.13 However, patients with high tissue or sputum eosinophil levels do not always have high blood eosinophil levels,14 although the correlation between blood and sputum eosinophilia in patients with asthma generally tends to be positive.[15], [16], [17] Given the indication from several smaller studies that higher sputum eosinophil levels might be positively associated with frequent asthma exacerbations6 and that eosinophil levels in sputum and blood are positively correlated, the authors hypothesized that higher blood eosinophil counts would be positively associated with more frequent self-reported asthma attacks in a general population of patients with asthma. To address this hypothesis, they examined the association between blood eosinophil counts and frequency of asthma attacks in patients with self-identified asthma in the National Health and Nutrition Examination Survey (NHANES) covering 10 survey years from 2001 through 2010.
Section snippets
NHANES Dataset
The NHANES is an annual survey of a nationally representative sample of the noninstitutionalized US civilian population. It is conducted by the National Center for Health Statistics of the Centers for Disease Control and Prevention. Each survey consists of a combination of an in-home interview, an examination at a mobile examination center, and laboratory tests. In each survey, participants are selected using a complex stratified multistage cluster sampling scheme. Ten survey years from 2001
Study Population
There were 1,441 children 6 to 17 years old and 1,721 adults 18 to 64 years old who self-identified as currently having asthma from 2001 through 2010 in this study. Mean age was 12 and 40 years for the pediatric and adult groups, respectively (Table 1). In children, there were more male than female patients (54% vs 46%), whereas the reverse was true in adults (63% vs 37%). Most patients were non-Hispanic white (55% of children and 72% of adults). Approximately two thirds of patients with asthma
Discussion
The authors' hypothesis was that in patients with asthma, a higher blood eosinophil count would be positively associated with more frequent asthma attacks. After controlling for potential confounders, the authors observed that higher blood eosinophil counts were associated with more frequent self-reported asthma attacks in children but not in adults in the analysis using 10 years of data. The association also was observed in adult patients when 2 additional potential confounders (FeNO and
Acknowledgments
The authors thank Drs Robert Zeiger and Michael Schatz for their review and input to the manuscript. They thank Dr Herve Caspard for input to the analysis of the data and review of the manuscript.
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Disclosure: Drs Tran and Ke are employees of Astrazeneca. Drs Khatry and Ward are employees of MedImmune. Dr Gossage is a former employee of MedImmune and a current employee of Gilead. The abstract was presented at the American Thoracic Society conference in San Diego, CA, May 16-21, 2014.