Sputum induction as a method of analyzing pulmonary cells: Reproducibilityand acceptability

Sputum induction has been proposed as a noninvasive method of sampling airw ay cells for assessing airway inflammation in asthma. Although useful in th e research setting, the applicability of this technique to a respiratory cl inic, where it might prove useful for clinical management of anti-inflammat ory therapy, has not been assessed. We therefore studied the effect of sput um induction in terms of patient acceptability, effect upon airway caliber, and reproducibility of the total cell and differential cell count at 2 wee ks in 20 asthmatic subjects first attending an asthma clinic. We compared s uch patients with normal controls. Thirty-seven subjects underwent sputum i nduction on two occasions (20 asthmatics and 17 normal subjects) separated by a 2-week interval, using a standardized protocol. Acceptability was asse ssed by questionnaire. Airway caliber was measured by serial spirometry, us ing albuterol premedication for asthmatic subjects. Sputum was induced by i nhalation of 3.5% saline over 12 min. Total cell and differential counts on induced sputum were assessed and correlated with bronchial hyperresponsive ness, as well as reproducibility of the technique in the clinical setting. All subjects found the process acceptable, xalthough mild side effects occu rred in more than 90% of subjects. No differences in acceptability were fou nd between asthmatic and normal subjects. Sputum induction was associated w ith a significant decrease in forced expiratory volume in 1 sec (FEV1) in n ormal subjects (from 4.1 +/- 0.17 to 4.02 +/- 0.19 L [p < 0.01] on visit 1 and on visit 2 from 4.01 +/- 0.15 to 3.90 +/- 0.16 L [p < 0.01]), but not i n asthmatic subjects after albuterol premedication. Total pulmonary cell yi eld on the first and second sputum induction days was 1.97 +/- 0.06 x 10(6) cells/mL of sputum and 2.01 +/- 0.05 x 10(6) cells/mL of sputum, respectiv ely, giving a reliability coefficient of 0.77. Less agreement was seen betw een individual cell differential counts within subjects, but most fell with in the expected range on Bland-Altman plots. Sputum induction appears to be safe and acceptable in both normal and asthmatic subjects. A small decreas e in FEV1 occurs in normal subjects, which is prevented by albuterol premed ication in asthmatics. Reproducibility at 2 weeks yielded similar total num bers of pulmonary cells, but ina clinic population some variability was see n in the number of inflammatory cells, probably because of the small number s of these cells. This technique may be less valuable ina:clinical than a r esearch setting.