Induced sputum : selection method.

Sputum consists of a mixture of mucus, inflammatory and epithelial cells, and cellular degradation products from the lower respiratory tract. In normal subjects, the inflammatory cells are mainly neutrophils and macrophages, with small numbers of lymphocytes, eosinophils, mast cells, and basophils. When expectorated the sputum is commonly contaminated with a variable amount of saliva, which has abundant squamous epithelial cells, and sometimes with secretions from the nasopharynx. These can be reduced by blowing the nose, rinsing the mouth, and swallowing water before expectoration. Contamination with saliva can be minimized by selecting the sputum from the expectorate and discarding the remainder. Selection of sputum (1) improves between-observer repeatability of differential cell counts (2,3) and allows standardization of measurements of total cell counts (expressed per gram of sputum) and fluid-phase mediators (by knowledge of the dilution factor of the processed sample).