Sputum induction in children with difficult asthma: safety, feasibility, and inflammatory cell pattern

Pediatr Pulmonol. 2005 Apr;39(4):318-24. doi: 10.1002/ppul.20159.


Difficult childhood asthma is defined by persistent symptoms despite maximal conventional therapy. We aimed to establish a safe method of sputum induction for these children and to study cytology and the relationship to exhaled nitric oxide (eNO). Sputum induction was performed in 38/40 children (aged 6-16 years) with difficult asthma, using 3.5% saline for four 5-min periods after bronchodilator pretreatment. Two children were excluded from sputum induction because postbronchodilator forced expired volume in 1 sec (FEV(1)) was <65% predicted. Seven of 38 children had symptoms (dyspnea and wheezing) during induction; of these, 3 experienced a fall in FEV(1) of >20% from postbronchodilator FEV(1), readily reversed with salbutamol. Sputum induction was successful in 28/38 children, with a higher success rate in children >/= 12 years than in younger children (87% vs. 50%, P = 0.02). Only 9/28 had abnormal sputum cytology; of these, 6 had predominant sputum eosinophilia (>2.5% eosinophils, </=54% neutrophils), while 3 had sputum neutrophilia (</=2.5% eosinophils, >54% neutrophils). Of 23 children with elevated eNO values, only 6 had sputum eosinophilia. In conclusion, sputum induction can be used to assess airway inflammation in children with difficult asthma, but abnormal sputum cytology is only present in a minority. Raised nitric oxide is only poorly predictive of sputum eosinophilia in these children.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Asthma / diagnosis*
  • Child
  • Eosinophils / cytology
  • Female
  • Forced Expiratory Volume
  • Humans
  • Inflammation / immunology
  • Male
  • Nitric Oxide / metabolism
  • Specimen Handling*
  • Spirometry
  • Sputum / cytology*


  • Nitric Oxide