Introduction With proposed NICE changes to the diagnosis of asthma,1 which recommend the use of fractional exhale nitric oxide (FeNO) at a positive value of ≥35 ppb and a change in direct challenge test (Methacholine) from 16 to 8 mg/ml as a cut off for positive responses, we have reviewed our data to assess the impact of these changes.
Methods A retrospective review of results from 2009 to 2016 where methacholine challenge tests (MCT) and FeNO were performed simultaneously in patients with normal spirometry in the assessment of airways disease.
Results Results were available on 145 patients and are tabulated below for both the cut off for MCH of 16 mg/ml (current)2 and the new cut off value of 8 mg/ml.
Conclusions Altering the threshold for MCT produces 10 less positive results (7%) reducing the clinical assumption of airways disease. Likewise, 17 had a positive FeNO and a negative challenge test irrespective of the MCT threshold. However, adopting this change reduced the number of negative FeNO and positive MCT from 32 to 22.
In our population, patients referred for a diagnosis of airways disease with normal spirometry showed a large number of patients were both negative for FeNO and MCT and changing the MCT threshold does not significantly impact our group.
NICE. Asthma: diagnosis and monitoring of asthma in adults, children and young people. Draft for Consultation. https://www.nice.org.uk/guidance/gid-cgwave0640/resources/asthma-diagnosis-and-monitoring-draft-guideline2 2015 (accessed 30 June 2016).
Crapo R, et al. Guidelines for methacholine and exercise challenge testing-1999. This official statement of the American Thoracic Society was adopted by the ATS Board of Directors, July 1999. AJRCCM 2000;161(1):309.
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