Asthma Management Handbook

Airway inflammation tests for diagnosis in adults

Recommendations

Do not routinely order induced sputum eosinophil count for all patients with suspected asthma. It is not necessary to demonstrate airway inflammation if the patient shows clinical features of asthma and there is a low probability that these are due to another cause.

How this recommendation was developed

Consensus

Based on clinical experience and expert opinion (informed by evidence, where available).

Measurement of exhaled nitric oxide is not recommended as a diagnostic test for asthma in routine clinical practice.

How this recommendation was developed

Consensus

Based on clinical experience and expert opinion (informed by evidence, where available), with particular reference to the following source(s):

  • Dweik et al. 20111

More information

Induced sputum test for eosinophilia in adults and adolescents

Patients with untreated asthma usually have airway inflammation (eosinophilic and/or neutrophilic), but testing for this is not essential for making the diagnosis of asthma in clinical practice. Some types of asthma are not associated with eosinophilic airway inflammation. 

The induced sputum test is not a standard microbiology test. It is provided by specialised laboratories.

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Exhaled nitric oxide (NO) testing in adults and adolescents

Measurement of the fraction of exhaled nitric oxide is not routinely used in Australian clinical practice, but is used in some hospitals and in some clinical trials.

In patients with symptoms that suggest asthma (e.g. wheeze, shortness of breath, variable cough), the finding of increased exhaled nitric oxide provides supportive evidence for an asthma diagnosis, but is not conclusive, because:1

  • some types of asthma (i.e. asthma without eosinophilic airway inflammation) are not associated with increased exhaled nitric oxide 
  • patients treated with inhaled corticosteroids may show a false negative test result.

In people with a clinical diagnosis of asthma, the exhaled nitric oxide test is useful for identifying those with asthma that is likely to respond well to inhaled corticosteroids. The exhaled nitric oxide test is easy for patients to do.

The predictive value of exhaled nitric oxide as a diagnostic test for asthma is higher than for peak expiratory flow and spirometry, and similar to that of bronchial challenge tests.1

There are several inflammatory phenotypes in asthma: eosinophilic, neutrophilic, mixed, and asthma with sputum cell counts within normal range (‘paucigranulocytic’). The exhaled nitric oxide fraction is associated with eosinophilic airway inflammation, but not with neutrophilic or paucigranulocytic asthma.1

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Impulse oscillometry in adults and adolescents

Impulse oscillometry is a noninvasive and rapid technique for measuring pulmonary function. Unlike spirometry, the test is easy to do and requires only passive cooperation by the patient, so it is suitable for small children. It is not used routinely in clinical practice, but is currently available in some tertiary referral centres.

Low-frequency impulse oscillometry (resistance at 5 Hz) measurements taken before and after administration of a bronchodilator correlate with spirometry (FEV1) in people with asthma and without asthma.2 Impulse oscillometry may be useful in identifying patients with asthma, and might possibly identify obstruction in the peripheral airways.3

This test is not used routinely in clinical practice because diagnostic cut-points are not well established yet.3 Australian normal values for adults without asthma have been developed.4

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References

  1. Dweik RA, Boggs PB, Erzurum SC, et al. An Official ATS Clinical Practice Guideline: Interpretation of Exhaled Nitric Oxide Levels (FeNO) for Clinical Applications. Am J Respir Crit Care Med. 2011; 184: 602-615. Available from: http://ajrccm.atsjournals.org/content/184/5/602.long
  2. Nair A, Ward J, Lipworth BJ. Comparison of bronchodilator response in patients with asthma and healthy subjects using spirometry and oscillometry. Ann Allergy Asthma Immunol. 2011; 107: 317-322. Available from: http://www.ncbi.nlm.nih.gov/pubmed/21962091
  3. Galant SP, Nickerson B. Lung function measurement in the assessment of childhood asthma: recent important developments. Curr Opin Allergy Clin Immunol. 2010; 10: 149-154. Available from: http://www.ncbi.nlm.nih.gov/pubmed/20035221
  4. Newbury W, Crockett A, Newbury J. A pilot study to evaluate Australian predictive equations for the impulse oscillometry system. Respirology. 2008; 13: 1070-1075. Available from: http://www.ncbi.nlm.nih.gov/pubmed/18699802