Correlation of Eosinophil Counts in Induced Sputum and Fractional Concentration of Exhaled Nitric Oxide and Lung Functions in Patients with Mild to Moderate Asthma

Background: The airway inflammation could be assessed by some noninvasive approaches. To investigate the value of eosinophil counts in induced sputum and fractional concentration of exhaled nitric oxide (FENO) for the regimen adjustment in patients with asthma, the correlation was analyzed between the two parameters and lung function parameter (forced expiratory volume in one second (FEV(1))).

Methods: Sixty-five outpatients with mild to moderate non-exacerbation asthma from Beijing Chao-Yang Hospital were enrolled as treatment group. Combined medications of inhaled corticosteroids plus long-acting beta-2 agonist were administered for one year. Lung function parameters, eosinophil counts in induced sputum, concentration of exhaled nitric oxide and the Asthma Control Test scores were recorded, at regular intervals in the follow-up period. Twenty-one healthy volunteers were enrolled as control group and underwent examination of eosinophil counts in induced sputum, lung function and concentration of exhaled nitric oxide.

Results: Sixty-three subjects from treatment group completed follow-up period for one year or longer. Mean FEV(1) value of the 63 subjects was (2.75 ± 0.54) L at baseline, (2.97 ± 0.56) L and (3.07 ± 0.52) L at month 3 and month 6, respectively, and maintained as (3.14 ± 0.51) L in the following six months. Mean FENO decreased from (61 ± 25) parts per billion (ppb) at baseline to (32 ± 19) ppb at month 3 (P < 0.05), and continued to decrease to (22 ± 12) ppb at month 6, the difference being significant when compared to both baseline and control group ((13 ± 8) ppb). Mean eosinophil counts decreased to (0.032 ± 0.011) × 10(6)/ml at month 3, which was significantly different from baseline ((0.093 ± 0.023)×10(6)/ml) and the control group ((0.005 ± 0.003)×10(6)/ml (both P < 0.05). The eosinophil counts in induced sputum correlated positively with concentration of FENO in the first six months (all P < 0.05). The concentration of FENO had a significant negative correlation with FEV(1) value (all P < 0.05) in any time point in the follow-up period. The Asthma Control Test scores were 18 ± 5, 19 ± 7, 23 ± 2, 24 ± 1 and 24 ± 1 at months 1, 3, 6, 9 and 12, respectively, which were significantly different from the score at baseline (14 ± 3) (P < 0.05). The most rapid clinical effect was observed at the second month after treatment.

Conclusion: Eosinophil counts in induced sputum and FENO are sensitive parameters to detect airway inflammation and may be useful in evaluating the efficacy of treatment and adjusting medication regimens.