Background
Induced sputum is a method to assess airway inflammation in clinical trials for asthma and COPD.^1–3 Sputum is a heterogeneous, viscous material containing inflammatory cell plugs, cellular debris, mucus, and saliva with squamous cells.

The quality of sputum cell preparations for differential cell count analysis depends on multiple factors and can be highly variable.^4,5 Percentage of squamous cell contamination (SQ%) is often used to assess the quality of sputum cell preparations.⁶ Here, we evaluated a comprehensive quality score,⁷ which also includes an assessment of the inflammatory cell morphology and amount of cellular debris.