Sputum Eosinophil Levels Correlate With Asthma Severity

Sputum eosinophil levels correlate with the severity of asthma clinical outcomes and response to inhaled corticosteroid treatment, according to a study published in the Journal of Asthma.

While forced expiratory volume during the first second (FEV1) is used to measure lung function in asthma, inflammation and remodeling can persist even when FEV1 has returned to normal. Bronchoscopy with biopsy and bronchoalveolar lavage may be used to monitor airway inflammation, but the invasiveness of these methods limits their use in clinical practice.

Sputum analysis offers a noninvasive alternative for assessing airway inflammation. Eosinophil infiltration plays an important role in the pathogenesis of asthma. Sputum eosinophil percentages are more accurate markers for asthma than blood eosinophil levels, but whether sputum eosinophil counts correlate with asthma severity was unknown until recently.

Researchers evaluated the relationship between sputum eosinophil levels and asthma severity, as measured by the following clinical parameters: days of acute exacerbations, days absent from school, emergency visits, nighttime cough, and use of salbutamol as rescue medication.

A total of 91 children (aged 7 to 18 years) with a new diagnosis of mild or moderate persistent asthma were treated with 3 months of inhaled budesonide. Induced sputum was collected at the time of enrollment and after 3 months of treatment. However, induced sputum could not be obtained in 6 children.

Patients with moderate persistent asthma had a higher percentage of sputum eosinophils than patients with mild persistent asthma at the time of enrollment (3.38% vs 2.99%; P =.001). Sputum eosinophil percentages in both groups at baseline were higher than normal (<1%).

Inhaled budesonide treatment for 3 months significantly reduced sputum eosinophil percentage in the entire study cohort (3.1% vs 0.06%; P <.0005).

After 3 months of inhaled budesonide therapy, sputum eosinophil percentages were similar in patients with mild vs moderate persistent asthma (0.07% vs 0.04%; P =.5104).

The difference in baseline sputum eosinophil levels between the mild and moderate asthma groups was no longer significant after 3 months of budesonide therapy, which, according to the researchers, suggests that both groups responded well to the treatment.

Higher sputum eosinophil counts were significantly associated with worse clinical outcomes for all 5 parameters measured. Lower sputum eosinophil levels correlated with improved FEV1 (P =.0001).

“[The] monitoring of asthma should involve not only the follow-up of symptoms and lung functions but also the determination of measure inflammatory markers by minimally invasive, safe and efficient techniques,” the researchers wrote.

“Sputum induction is an easy and safe method of obtaining samples with a high success rate. Eosinophil count measurement is cheap as compared to other markers like a fraction of exhaled nitric oxide measurement,” they noted.

Study limitations included the lack of a control group and short follow-up (3 months). “Further studies with a larger sample size and longer follow-up are required for dose adjustments of [inhaled corticosteroids] according to sputum eosinophil count and for the reduction of the steroid toxicity by using minimal therapeutic maintenance dose of steroid,” the researchers concluded.

Reference

Kansal P, Nandan D, Agarwal S, Patharia N, Arya N. Correlation of induced sputum eosinophil levels with clinical parameters in mild and moderate persistent asthma in children aged 7-18 years [published online July 11, 2017]. J Asthma. doi:10.1080/02770903.2017.1338725