Induced Sputum Analysis in Airway Inflammation

Induced sputum analysis has emerged as a pivotal non-invasive technique for characterising airway inflammation in a range of respiratory disorders. By inhalation of hypertonic saline to provoke sputum expectoration, clinicians and researchers obtain samples that reflect the cellular and biochemical milieu of the lower airways. Differential cell counts—principally eosinophils, neutrophils, lymphocytes and macrophages—provide a window into distinct inflammatory endotypes, guiding therapeutic decisions such as inhaled corticosteroid dosing or targeted biologic therapy. Biochemical assays of sputum supernatant yield quantification of cytokines, chemokines and protein mediators, enhancing understanding of disease mechanisms and treatment responses. Standardisation of induction protocols, careful sample processing and rigorous quality control are essential to ensure reproducibility across centres. With growing evidence for its role in asthma, chronic obstructive pulmonary disease and other inflammatory airway disorders, induced sputum analysis is increasingly recognised for its capacity to inform personalised management, monitor therapeutic efficacy and drive discovery of novel biomarkers.

Research from Nature Portfolio

Recent cross-sectional work has examined the relationship between sputum eosinophilia and clinical outcomes in adult asthma, revealing that a threshold of 3 percent eosinophils in induced sputum does not reliably correlate with standard measures of asthma control or patient-reported quality of life. These findings prompt a reevaluation of sole reliance on eosinophil counts for guiding treatment in severe disease. In a separate study of mechanically ventilated patients, investigators have standardised mechanical mucus dissolution for bronchial secretions, demonstrating that physical disruption—rather than chemical agents alone—yields higher cell recovery and more accurate protein measurements. This methodological advance emphasises the need for consistent sample handling and indicates that sampling technique can substantially influence interpretation of airway inflammation in critical care settings.

Induced Sputum Analysis in Airway Inflammation publication trend

The graph below shows the total number of articles in induced sputum analysis in airway inflammation across all publications each year (not limited to Nature Index journals).

Technical terms

Induced sputum: Respiratory sample obtained by inhalation of a hypertonic saline aerosol to provoke expectoration of lower airway secretions.

Eosinophil: White blood cell involved in type 2 inflammatory responses, commonly elevated in allergic asthma and certain airway endotypes.

Neutrophil: Predominant inflammatory cell in innate immunity, often linked to bacterial infection and non-eosinophilic airway inflammation.

Dithiothreitol (DTT): Reducing agent used to liquefy sputum by breaking disulphide bonds in mucus, facilitating cellular analysis.

Cytokine: Small protein mediator released by immune cells that regulates inflammation, cell recruitment and tissue responses.

References

1. Asthma control and sputum eosinophils in adult patients: a cross-sectional study in southern Brazil. Scientific Reports (2023).
2. Methodological Aspects of Induced Sputum. Advances in respiratory medicine (2023).
3. Sputum processing by mechanical dissociation: A rapid alternative to traditional sputum assessment approaches. The Clinical Respiratory Journal (2021).
4. Improved cytometric analysis of untouched lung leukocytes by enzymatic liquefaction of sputum samples. Biological Procedures Online (2022).
5. Sputum induction and its diagnostic applications in inflammatory airway disorders: a review. Frontiers in Allergy (2023).
6. Evaluation of airway inflammation in mechanically ventilated patients using cell count and protein concentration. Scientific Reports (2021).