SPONTANEOUS AND INDUCED SPUTUM TO MEASURE INDEXES OF AIRWAY INFLAMMATION IN ASTHMA

Inhalation of hypertonic saline to induce sputum may alter cells and f luid-phase markers in sputum. We have compared indices of inflammation in sputum produced spontaneously with sputum induced by an aerosol of hypertonic saline. Twenty-three asthmatics produced spontaneous follo wed by induced sputum on the same day. The sputum specimen was separat ed from saliva within 2 h, dispersed with dithiothreitol (DTT) and pro cessed to obtain cytospins and supernatant. The statistical power to d etect a 20% difference in sputum parameters was > 90%. Results are exp ressed as median and interquartile range [IQR]. Induced sputum had a h igher proportion of viable cells (77.0 [19.0] versus 47.0 [38.0]%, p < 0.001), less squamous cell contamination (1.0 [1.2] versus 1.8 [34.0] %, p < 0.001) and better quality cytospins (score of 8.0 [4.0] versus 4.0 [2.0], p < 0.001). It also had lower fluid-phase levels of eosinop hil cationic protein (ECP) (1,358 [1,102] versus 1,574 [2,479] mu g/L) and fibrinogen (1,560.0 [3,130.0] versus 4,350.0 [5,970.0] ng/ml) but only the latter was significantly different (p = 0.02). induced sputu m was similar to spontaneous sputum in weight (200.0 [219.0] versus 27 0.0 [227.0] mg), total cell count (3.3 [4.1] versus 3.5 [4.5] x 10(6)/ ml), proportion of nonsquamous cells, and levels of tryptase. The agre ement between induced and spontaneous measurements was good, but fluid -phase levels were affected by the low viability of some spontaneous s amples. We conclude that for the indices measured in asthmatic subject s, induced sputum separated from saliva is similar to lower respirator y secretions expectorated spontaneously and has the advantage of bette r cell viability.