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Induced sputum: time from expectoration to processing

Asthma Research Group, Firestone Institute for Respiratory Health, St Joseph's Healthcare and McMaster University, Hamilton, Ontario, Canada

CORRESPONDENCE: F.E. Hargreave, Firestone Institute for Respiratory Health, St. Joseph's Healthcare, 50 Charlton Ave. East, Hamilton, ON, Canada, L8N 4A6. Fax: 1 9055216158. E-mail: hargreav@mcmaster.ca

Keywords: induced sputum, sputum cell counts, sputum chemistry

Received: December 12, 2000
Accepted November 16, 2001

This study was supported by a Medical School Grant from Merck Frosst Inc.

One of the limitations in the use of induced sputum to measure indices of airway inflammation is the perceived need to process the sample within 2 h. Therefore, the authors investigated whether the processing of induced sputum could be delayed.

Induced sputum samples obtained from asthmatic subjects (n=30) were examined. Each sample was stored at 4°C. A portion was selected and processed within 2 h and the remaining expectorate (sputum plus saliva) was refrigerated. Later an equal amount was selected and processed at either 9 (n=15) or 18 (n=15) h. The sputum was examined for cell counts and viability, fluid-phase eosinophil cationic protein (ECP), interleukin-8 (IL-8) and fibrinogen. Repeatability of measurements was assessed by the interclass correlation coefficient (ICC).

Measurements obtained at 9 h did not differ from those made at 2 h and the repeatability was excellent (ICC 0.88–0.99). However, by 18 h the median cell viability was reduced from 65.0% to 43.0% and the ICC was generally lower: 0.10 for total cell count, 0.24 for viability, 0.60 for neutrophils, 0.90 for eosinophils, 0.56 for macrophages, 0.76 for ECP, 0.82 for IL-8 and 0.84 for fibrinogen.

The results indicate that when induced sputum from subjects with asthma is kept at 4°C, examination of cell counts can be delayed for 9 h and for the fluid-phase indices measured for 18 h. Further investigation of this issue is required for spontaneous sputum, other airway diseases and other inflammatory markers.

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