INDUCED SPUTUM TO ASSESS AIRWAY INFLAMMATION - A STUDY OF REPRODUCIBILITY

Background Infiltration of the airways mucosa with activated inflammat ory cells appears to be a major factor in the pathogenesis of asthma a nd other airway diseases. Examination of sputum provides a direct meth od to investigate airway inflammation non-invasively. Objectives The a im of the present study was to evaluate the reproducibility of cell co unts on cytospins and fluid phase (eosinophil cationic protein, ECP) m easurements in a selected portion of induced sputum. We aimed to confi rm the validity of the tecnique by comparing measurements between stab le asthmatics, allergic rhinithis and healthy subjects. Methods Sputum was induced with hypertonic saline (4.5%) twice within one week in 53 stable asthmatics, 16 subjects with seasonal rhinitis (out of the pol len season), and 19 healthy subjects. Reproducibility was examined wit hin sample (two different plugs of the same sample) between sample (tw o specimens of induced sputum obtained within one week) and between ex aminers on stable subjects taking into account sample size, number of examinations per patients and Confidence Interval (CI) of the estimate s. Results We have found that the method is highly reproducible within sample and between examiners for all types of cells and fluid phase m easurements of ECP. It is reproducible between sample for eosinophils, macrophages, neutrophils and ECP, but not for lymphocytes and weakly for epithelial cells. Sputum from asthmatics, in comparison with the s putum of healthy subjects and subjects with rhinitis had higher eosino phils (asthmatics: 12.2% +/- 12.9, rhinitis: 0.4 +/- 0.8, normals: 0.4 +/- 0.7(%) and ECP (asthmatics: 827 +/- 491 mu g/L, rhinitis: 127 +/- 82 normals: 157 +/- 203). No significant differences were found betwe en healthy subjects and subjects with rhinitis. Eosinophil counts were inversely correlated with FEV1 (r = -0.37) expressed as percentage of predicted, but not significantly correlated with PC20 methacholine (r = -0.28) or blood eosinophils (r = 0.26). Conclusions The importance of this study is the confirmation, within important statistical guidel ines for a study of reproducibility, that the methods examined are rep roducible and valid.