Q&A

Use of sputum eosinophil count decreases asthma exacerbations

J Fam Pract. 2003 May;52(5):349-364
By
Heather Bittner Fagan, MD
Marc Harwood, MD
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  • BACKGROUND: Asthma exacerbations are preceded by airway hyperresponsiveness; proinflammatory cells, including eosinophils, are implicated as the cause. Sputum eosinophilia develops weeks before an asthma exacerbation, and reduction of sputum eosinophilia often parallels the reduction of asthma symptoms. Therefore, regular testing for sputum eosinophils could allow physicians to predict and prevent severe asthma exacerbations.
  • POPULATION STUDIED: Patients, aged 18 to 75 years, were recruited from 1 of 3 specialist clinics. Subjects had moderate to severe asthma. The study excluded current smokers, former smokers with >15 pack-year tobacco history, patients with inadequately controlled gastroesophageal reflux disease or rhinitis, patients with a severe asthma exacerbation within 4 weeks of entry, and patients considered to be poorly compliant.
  • STUDY DESIGN AND VALIDITY: Patients were randomized to receive treatment based on the British Thoracic Society (BTS) guidelines or treatment based on eosinophil counts. Patients in the BTS management group were managed during exacerbations according to guidelines similar to the National Institute of Health’s stepwise approach to asthma management. The sputum management group was managed according to a preset treatment algorithm; in this group, treatment with steroids or bronchodilators was initiated based on changes in eosinophil count rather than when symptoms appeared.
  • OUTCOMES MEASURED: The primary outcome measured was severe asthma exacerbations, defined by the authors as a minimum 30% decrease morning peak expiratory flow on 2 consecutive days, or symptoms requiring treatment with oral steroids. Other outcomes included quality of life (measured using an asthma quality-of-life questionnaire), the use of B2 agonist rescue medications, symptoms (measured using a visual analog scale), and postbronchodilator pulmonary function. In addition, the researchers also evaluated the number of rescue courses of steroids, amount of steroids per patient day, and number of hospitalizations required for each patient.
  • RESULTS: The sputum management group had fewer severe exacerbations compared with the BTS group (35 vs 109, respectively; P.=.01) and fewer hospitalizations (1 vs 6, P.=.047). These data translate into a number needed to treat for benefit of 7 (95% confidence interval [CI], 3–100). Based on this confidence interval—the result of a small sample size—one more hospitalization in either group could have strongly affected the number needed to treat for benefit.
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PRACTICE RECOMMENDATIONS

The use of regular sputum eosinophil counts to initiate and follow treatment in patients with asthma produced a small decrease in the number of hospitalizations and asthma exacerbations in compliant, moderate-to-severe asthmatics.

The definition of asthma exacerbation used in this study (a 30% decrease in morning peak expiratory flow on 2 consecutive days or initiation of oral corticosteroids) may not be clinically relevant.

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