Sputum processing by mechanical dissociation: A rapid alternative to traditional sputum assessment approaches

Sputum cytology is currently the gold standard to evaluate cellular inflammation in the airways and phenotyping patients with airways diseases. Sputum eosinophil proportions have been used to guide treatment for moderate to severe asthma. Furthermore, raised sputum neutrophils are associated with poor disease control and impaired lung function in both asthma and COPD and small airways disease in cystic fibrosis. However, induced-sputum analysis is subjective and resource heavy, requiring dedicated specialist processing and assessment; this limits its utility in most clinical settings. Indirect blood eosinophil measures have been adopted in clinical care. However, there are currently no good peripheral blood biomarkers of airway neutrophils. A resource-light sputum processing approach could thus help integrate induced sputum more readily into routine clinical care. New mechanical disruption (MD) methods can rapidly obtain viable single cell suspensions from sputum samples.

The aim of this study was to compare MD sputum processing to traditional methods for cell viability, granulocyte proportions and sputum cytokine analysis.

Sputum plugs were split and processed using traditional methods and the MD method, and samples were then compared.

The MD method produced a homogeneous cell suspension in 62 s; 70 min faster than the standard method used. No significant difference was seen between the cell viability (p = 0.09), or the concentration of eosinophils (p = 0.83), neutrophils (p = 0.99) or interleukin-8 (p = 0.86) using MD.

This cost-effective method of sputum processing could provide a more pragmatic, sustainable means of directly monitoring the airway milieu. Therefore, we recommend this method be taken forward for further investigation.