Sputum Induction in Corticosteroid-Dependant Asthmatics: Risks and Airway Cellular Profile

Sputum induction with nebulized hypertonic saline is increasingly being used to evaluate airway in-flammation. We investigated the procedure-associated risk in 16 asthmatics that were still symptomatic despite on high doses of regular corticosteroid (CS) therapy (7 on daily inhaled CS ≥ 800 μg budesonide or equivalent; 9 on additional daily oral CS) and their sputum cellular profile. For comparison, 12 mild stable asthmatics and 10 normal healthy subjects were included. All subjects inhaled 3%, 4% and 5% hypertonic saline sequentially via ultrasonic nebulizer as a means to induce sputum. Maximal percentage fall of Forced Expiratory Volume on One Second (FEV 1) during sputum induction was significantly greater in CS-dependent asthmatics (median % [IQR]: 16.0 [11.0-32.3]) than in mild asthmatics (5.3 [4.2-10.8], p = 0.002] and in normal subjects (4.6 [3.4-6.4]), p = 0.0001). The maximal percentage FEV1 fall was inversely correlated with baseline FEV1 ( R s= -0.69; p < 0.0001). Compared to mild asthmatics, induced sputum from CS-dependant asthmatics had proportionately fewer eosinophils (2.2 [0.8-7.0] versus 23.3% [10.7-46.3], p = 0.003) and greater neutrophils (64.2 [43.9-81.2] versus 28.7 [19.0-42.6], p = 0.009). Sputum neutrophils showed a significant inverse correlation to FEV1 ( R s = -0.51, p = 0.01). We concluded that sputum induction using nebulized hypertonic saline should be performed with caution in CS-dependant asth-matics. The airway cellular profile observed suggests that the immunopathology underlying CS-dependant asthmat-ics may be different or a consequence of CS therapy.