Establishing a Normal Range for Induced Sputum Cell Counts in Western Canada

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BACKGROUND: Induced sputum cell counts are a noninvasive, reliable method for evaluating the presence, type and degree of airway inflammation. Whether current reference values for induced sputum cell counts are applicable in other induced-sputum laboratories, particularly those in Western Canada or at elevated altitude, is not clear.OBJECTIVES: To describe the normal range of induced sputum cell counts in healthy adults in Western Canada.METHODS: A total of 105 healthy nonsmoking adults with normal bronchial responsiveness and no history of lung disease proceeded with sputum induction. Sputum samples were fixed in formalin.RESULTS: Sixty-nine subjects were included in the final analyses. The mean ± SD and median (interquartile range) of the cell counts, respectively, were: total cell count 2.453±2.108, 2.000 (2.512); neutrophils 1.212±1.491, 0.721 (1.016); eosinophils 0.034±0.069, 0.005 (0.043); macrophages 1.050±1.213, 0.696 (1.005); lymphocytes 0.057±0.161, 0.001 (0.049); and bronchial epithelial cells 0.041±0.126, 0.000 (0.027). The respective differential cell percentages were: neutrophils 50.3±23.5, 51.9 (32); eosinophils 1.4±2.3, 0.3 (2); macrophages 43±22.8, 39.3 (32); lymphocytes 2.6±5.2, 0.4 (2.5); and bronchial epithelial cells 2.2±4.8, 0.0 (2.9). Bland-Altman analysis and intraclass correlation coefficients revealed excellent interobserver agreement for measurement of sputum cell types.DISCUSSION: The range of induced sputum cell counts performed in a laboratory in Western Canada in healthy nonsmoking adult subjects was described; cellular distributions were similar to previous studies. This was also the first description of normal values for formalin-fixed induced sputum samples.CONCLUSIONS: These results confirm that current reference values for induced sputum are generalizable across different laboratories, including those in Western Canada and those at elevated altitude, and are also generalizable to formalin-fixed samples, allowing use in the broader Canadian asthma population.
Warren J Davidson, Stephanie The, and Richard Leigh, “Establishing a Normal Range for Induced Sputum Cell Counts in Western Canada,” Canadian Respiratory Journal, vol. 20, no. 6, pp. 424-428, 2013. doi:10.1155/2013/547309