Re: Dorman SC, Bussoli MA, Ritz SA. Alcohol fixation of induced sputum samples for applications in rural communities. Can Respir J 2010;17:115-121

Establishing a normal range for induced sputum cell counts in Western Canada

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.

The impact of diurnal variation on induced sputum cell counts in healthy adults

BACKGROUND

Induced sputum cell counts are a non-invasive, reliable method for evaluating the presence, type, and degree of inflammation in the airways of the lungs. Current reference values for induced sputum cell counts in healthy adults do not account for the effects of circadian rhythm, including diurnal variation. The objective of this study was to describe the diurnal variation in induced sputum cell counts, compared between early morning and late afternoon, in healthy adult individuals.

METHODS

100 healthy adult subjects with no history of lung disease and normal bronchial reactivity proceeded with induced sputum testing at 7 am and 4 pm on different days. The order of testing was randomized. The cytotechnologist preparing and performing the cell counts was blinded to the sample collection time and subject characteristics.

RESULTS

65 subjects were included in the final analyses. There was no significant change in the total and differential sputum cell counts between the 7 am and 4 pm collections. There was good inter-observer agreement with respect to differential sputum cell count interpretation.

CONCLUSIONS

This is the largest study to assess the variation in induced sputum cell counts in healthy adult subjects at different times of the day. We found no significant change in total and differential sputum cell counts between the 7 am and 4 pm collection time points. This is in contrast to studies in asthmatics that demonstrated a circadian variation in sputum cell counts and other markers of inflammation, suggesting that fluctuations in airway inflammatory cells during the day are a disease-specific effect.