Usefulness of induced sputum eosinophil count to assess severity and treatment outcome in asthma patients

Abstract

Context: Currently treatment decisions in asthma are governed by clinical assessment and spirometry. Sputum eosinophil, being a marker of airway inflammation, can serve as a tool for assessing severity and response to treatment in asthma patients.

Aims: To establish correlation between change in sputum eosinophil count and forced expiratory volume in one second (FEV1)% predicted value of asthma patients in response to treatment. In this study, we also predicted prognosis and treatment outcome of asthma patients from baseline sputum eosinophil count.

Settings and design: A longitudinal study was conducted to determine the treatment outcome among newly diagnosed asthma patients who were classified into A (n = 80) and B (n = 80) groups on the basis of initial sputum eosinophil count (A ≥ 3% and B < 3%).

Materials and methods: After starting treatment according to Global Initiative for Asthma Guideline, both A and B groups were evaluated every 15 days interval for the 1(st) month and monthly thereafter for a total duration of 12 months. In each follow-up visit detailed history, induced sputum eosinophil count and spirometry were done to evaluate severity and treatment outcome.

Results: FEV1% predicted of group A asthma patients gradually increased and sputum eosinophil count gradually decreased on treatment. Longer time was required to achieve satisfactory improvement (FEV1% predicted) in asthma patients with sputum eosinophil count ≥3%. There was statistically significant negative correlation between FEV1% predicted and sputum eosinophil count (%) in of group A patients in each follow-up visit, with most significant negative correlation found in 8(th) visit (r = -0.9237 and P = < 0.001). Change in mean FEV1% (predicted) from baseline showed strong positive correlation (r = 0.976) with change in reduction of mean sputum eosinophil count at each follow-up visits in group A patients.

Conclusions: Sputum eosinophil count, being an excellent biomarker of airway inflammation, can serve as a useful marker to assess disease severity, treatment outcome, and prognosis in asthma patients.

Keywords: Asthma; forced expiratory volume in one second; induced sputum; sputum eosinophil count; treatment outcome.

Figure 1

Flow chart describing the patient flow and study method

Figure 2

Line diagrams showing outcome variables (mean no. of sleep disturbances, performance of daily activity, control status, and no. of exacerbations) of group A and group B during initial and follow-up visits

Figure 3

(a) Line diagram showing sputum eosinophil count (%) of group A and group B during initial and follow-up visits. (b) Line diagram showing FEV₁% predicted of group A and group B during initial and follow-up visits

Figure 4

Scatter plot showing correlation between changes in mean FEV₁ (% predicted) and change in reduction of mean sputum eosinophil count (%) during follow-up visits in group A