Concordance for changes in allergic asthma domain variables after short-term corticosteroid therapy

Asthma is a complex syndrome with multiple domains including symptoms, lung function, asthma control, and airway inflammation. A study of Fenom PRO™, a novel monitor for exhaled nitric oxide (FeNO), provided an opportunity to look at concordance/discordance (C/D) for changes in multiple asthma domains over a 2-week period after corticosteroid therapy.

Non-steroid-treated adults and children with uncontrolled asthma had asthma domain measures, (FeNO), forced expired volume in 1 s (FEV₁), the 6-item Asthma Control Questionnaire scores (ACQ6), and daily asthma symptoms, assessed before and after a 2-week course of corticosteroids. Asthma symptoms were assessed using a custom novel twice-daily symptom scale (ASX). C/D bidirectional changes in all domains were calculated around both the zero point, and around the minimal important difference (MID) in relevant subjects.

There was a highly significant fall in mean FeNO of 51.7% over 2 weeks (p < 0.0001) accompanied by significant improvements in mean FEV₁, ACQ6 and ASX scores. However, C/D between individual domains varied considerably between subjects. The C/D between parameters for any change around zero for the combined adults and pediatric population was best for FeNO and ACQ6, 79.3/20.7% while FEV₁ was more discordant than other parameters in general. When considering changes around the minimal important difference (MID) in a subset, the level of concordance increased in general, with FeNO and ACQ6 demonstrating a C/D of 93.5/6.6%.

This data demonstrates that the concordance between changes in the asthma domains is often substantially less than 100%. Reasons for this may include different time courses for change of the separate domains, the degree of abnormality for each domain at baseline, as well as intrinsic limitations of each parameter.