Elevated Blood Eosinophil Levels Predict Asthma Exacerbations

In adults with persistent asthma, elevated blood eosinophil levels may be able to predict which individuals are at increased risk for exacerbations.

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

Physicians at Kaiser Permanente (San Diego, CA, USA) measured blood eosinophil level 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, comorbidities, and asthma burden and care.

The scientists found that 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 greater than 300/mm³ with crude rate ratio 1.25, but was weaker after adjustment for baseline characteristics with an adjusted rate ratio 1.16.

In 2011, after adjustment for baseline features, the adjusted rate ratio of 1.31, which was highly significant, the authors concluded that a baseline eosinophil level of greater than 400/mm³ was associated with future asthma exacerbations. Other factors in 2010 that were significantly associated with an increased risk of exacerbations in 2011 included a history of prior asthma exacerbations, Global Initiative for Asthma (GINA) steps-4/5, dispensing of seven or more short-acting beta-agonist canisters, female gender, black ethnicity, and obesity.

Robert S. Zeiger, MD, PhD, the Physician Investigator at Kaiser Permanente, said, “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. In our study, elevated blood eosinophil levels were found to be a risk factor for subsequent exacerbations in adult asthma patients”.

Dr. Zeiger added “Our findings suggest that asthma patients with an elevated blood eosinophil level have a greater disease burden. 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.” The study was presented at the American Thoracic Society International Conference, held May 16–21, 2014, in San Diego (CA, USA).

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