title: The impact of diurnal variation on induced sputum cell counts in healthy adults.
abstract: 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.
authors.affiliation: Department of Medicine, University of Calgary, 7007-14th Street SW, Calgary, Alberta, T2V 1P9, Canada.
authors.forename: Warren J
authors.initials: WJ
authors.lastname: Davidson
authors.affiliation: Faculty of Kinesiology, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Lisa E
authors.initials: LE
authors.lastname: Wong
authors.affiliation: Department of Medicine, University of Calgary, 7007-14th Street SW, Calgary, Alberta, T2V 1P9, Canada.
authors.forename: Stephanie
authors.initials: S
authors.lastname: The
authors.affiliation: Department of Medicine, University of Calgary, 7007-14th Street SW, Calgary, Alberta, T2V 1P9, Canada.
authors.forename: Richard
authors.initials: R
authors.lastname: Leigh
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