Induced sputum cellularity: Reference values and distribution in normal volunteers

Sputum induction has recently been proposed as the only direct noninvasive method for measuring airway inflammatory indices. The reference values and the distribution of cells in induced sputum in a control population have not yet been well defined. We therefore evaluated data from a large number of healthy volunteers. One hundred fourteen healthy, nonatopic, nonsmoking volunteers without airway hyperreactivity were enrolled (age: 38 ± 13 yr [mean ± SD]; FEV₁: 105 ± 10% predicted; provocative dose of methacholine inducing a 20% decrease FEV₁ > 3,200 μg). Ninety-six subjects (84%) produced adequate analysis samples. The subjects had a normal age distribution. Their induced sputum was rich in macrophages (69.2 ± 13%) and neutrophils (27.3 ± 13%), and poor in eosinophils (0.6 ± 0.8%), lymphocytes (1.0 ± 1.2%), and epithelial cells (1.5 ± 1.8%). Only macrophages and neutrophils showed a normal distribution; total and differential counts of other cells did not. We propose that these data be used in comparison of the induced sputum cells of normal subjects and those of patients with airway inflammation.