Exhaled biomarkers show limited value in gauging asthma control
MedWire News: Assessment of gas and pH levels in exhaled breath may offer a new way to gauge asthma control, according to researchers writing in the journal Respiratory Medicine.
Konstantinos Kostikas (University of Thessaly Medical School, Larissa, Greece) and co-workers tested the value of exhaled breath assessment as a surrogate for airway inflammation in 274 consecutive patients with asthma.
They focused on two biomarkers that can be measured non-invasively: exhaled nitric oxide (FeNO; assessed using a portable analyzer) and exhaled breath condensate pH (EBC; assessed after Argon deaeration using the EcoScreen device).
All participants were also evaluated for asthma control using the Global Initiative for Asthma (GINA) guidelines as well as the asthma control test (ACT) and asthma control questionnaire (ACQ).
Overall, 99 patients were classified as having "well-controlled" asthma, 115 as "partly controlled," and 60 as "uncontrolled."
Both FeNO and EBC pH differed significantly according to asthma control, Kostikas's team reports.
Specifically, mean FeNO was 16, 27, and 59 in well-controlled, partly-controlled, and uncontrolled patients, respectively, while mean EBC pH was 7.44, 7.25, and 7.14 in the three groups, respectively.
Furthermore, analysis of the area under receiver operating characteristic curves (AUC) indicated that FeNO had a value of 0.790 for discriminating well-controlled from partly controlled/uncontrolled disease, and performed better in non-smokers, whereas EBC pH had an AUC of 0.791 and performed better in smokers.
Neither of these biomarkers, either alone or combined, was superior to clinical judgment, the ACT, or the ACQ, however.
Finally, a FeNO cutoff of 30 ppb had a positive predictive value (PPV) of >85% (with the exception of smokers treated with inhaled corticosteroids); an EBC pH cutoff of 7.20 had a PPV >80% in all patients, and the combination of the markers - ie, FeNO >30 ppb and/or EBC pH ≤7.20 was indicative of poorly controlled/uncontrolled asthma in 88.3% of patients.
"FeNO and EBC pH levels may be useful in the identification of patients with [poorly controlled/uncontrolled] asthma," the team concludes.
"Further longitudinal studies for the prospective evaluation of the performance of the two biomarkers to guide the management asthmatic patients are clearly justified."
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By Joanna Lyford