Some technical factors influencing the induction of sputum for cell analysis

Inhalation of hypertonic saline aerosol is a relatively noninvasive method to obtain sputum for examination of inflammatory processes in the airways. We investigated some technical factors which might influence the success of induction and sputum cell counts. In total, twenty six asthmatic and 13 healthy subjects, unable to raise sputum spontaneously, inhaled nebulized saline for three 7 min intervals. In three randomized, cross-over studies we repeated sputum induction on separate days with two ultrasonic nebulizers (De Vilbiss Ultraneb 99 and Fisoneb) and one jet nebulizer (Pari LL with Master Compressor) (Study 1, n = 15), with different saline concentrations (normal saline 0.9%; hypertonic saline 3% on 2 days; and hypertonic saline 3, 4 and 5%, sequentially) (Study 2, n = 14) and with pretreatment with either salbutamol or placebo (Study 3, n = 10). The latter two studies were double-blind. Sputum cells were dispersed with dithiothreitol, and the cell suspension was used to perform total cell counts and to prepare cytospins for differential cell counts. We compared success rate, cell counts, subject discomfort and percentage fall in forced expiratory volume in one second (FEV1) during the procedures. All sputum examinations were performed blind to the clinical procedures. The success rates and the cell counts of the specimens obtained with the two ultrasonic nebulizers were not different, whilst general discomfort was proportional to the saline output of the nebulizer. Induction of sputum by hypertonic saline was more successful than normal saline, but more disagreeable to the subjects. Induction with saline 3% on two days was only successful in 6 of 14 subjects.(ABSTRACT TRUNCATED AT 250 WORDS)