Baseline Sputum Parameters in Normals, Asthmatics, COPD, Atopics, Smokers and Ex-Smokers

Rationale: Induced sputum is widely used in both research and industry-based clinical trials to evaluate changes in cellular and biochemical constituents in the central airways. Data is lacking however on baseline sputum parameters in large cohorts of healthy and diseased subjects.

Methods: Uniform methods for induction (3, 4, 5%, 21 minutes) and processing (plug selection with DTT) were used on normals (N=148), asthmatics (N=97), COPD (N=200), atopics (N=195), otherwise healthy smokers (N=43), atopic smokers (N=45) and ex-smokers (N=47). Endpoints examined included initial raw sample weight, selected plug weight, total and differential cell counts, cell viability, induction success, slide quality score and slide readability.

Results: COPD subjects produced significantly less raw sputum (2667mg) and selected plug material (1320 mg) but yielded significantly (p<0.05) higher total cell counts (4.7x10⁶ cells; 6420 cells/mg) and PMN levels (80%; 5831 pmn/mg) vs all other subject cohorts. Percent PMN levels in normals and asthmatics were equal (28%) but asthmatics had the lowest absolute PMN/mg count (259 PMN/mg) vs all subjects. Interestingly, COPD subjects demonstrated the highest and lowest % Eos (2.2%) and % Lym (0.3%), respectively vs all subjects. Cell viability was lowest among atopics (65%) and highest among COPD (78%). Asthmatics demonstrated the poorest ability to produce sputum (71% success rate) and smokers were the best (95%). Slide quality score and slide readability did not differ significantly among the subject cohorts analyzed.

Conclusions: Baseline sputum parameters differ among healthy and diseased subjects. These differences can inform important decisions regarding subject recruitment, study design and optimal application of sputum.