Induced sputum in asthma: diagnostic and therapeutic implications

Induced sputum provides a noninvasive way of assessing airway disease. This has led to the identification of different phenotypes of asthma and the potential for individualized treatment targeted at specific pathological processes. However, practical issues limit the frequent use of this technique. This review assesses the extent to which induced sputum can distinguish between asthma phenotypes and guide treatment.

Although the short-term repeatability of sputum analysis is good, recent research has shown a great deal of variability in sputum inflammatory profiles over follow-up periods of several months to a few years. In particular, the distinction between eosinophilic and noneosinophilic asthma is not consistent in many individuals. These findings suggest that persistent asthma phenotypes cannot be determined using a single sputum sample. Recent studies have also cast doubt on previous findings that noneosinophilic asthma is unresponsive to corticosteroid treatment.

Sputum inflammatory profiles are not consistent over time and a persistent asthma phenotype cannot be reliably determined using a single induced sputum. Because time and cost issues prohibit frequent induced sputum analyses in most clinical settings, these findings limit the diagnostic and therapeutic value of sputum analysis for clincal practice.