FeNO measurement identifies eosinophilic asthma
MedWire News: Results from a Belgian study suggest that fractional exhaled nitric oxide (FeNO) measurements can distinguish eosinophilic from non-eosinophilic asthma.
Writing in the journal Thorax, Florence Schleich (University of Liege) and colleagues explain: "It has been claimed that FeNO could be regarded as a surrogate marker for sputum eosinophil count in patients with asthma.
"However, the FeNO threshold value that identifies a sputum eosinophil count of at least 3% in an unselected population of patients with asthma has been poorly studied."
To investigate further, the team studied 295 patients with asthma, aged 15-84 years, who underwent FeNO measurement and sputum induction for assessment of eosinophil levels.
The participants also completed questionnaires detailing their use of asthma medications, allergic status, age, and other variables.
Receiver operating characteristic curve analysis revealed that, in the whole cohort, a FeNO level of 41 parts per billion (ppb) or higher was 65% sensitive and 79% specific for identifying eosinophilic asthma (a sputum eosinophil level of 3% or higher).
This was confirmed with logistic regression analysis, which showed that, in the whole cohort, a FeNO threshold of 42 ppb distinguished eosinophilic from non-eosinophilic asthma with a sensitivity of 63% and a specificity of 80%.
Further analysis showed that the FeNO threshold associated with eosinophilic asthma was significantly lower, at 27 ppb, in patients receiving high doses of inhaled corticosteroids (at least 1000 µg beclometasone) compared with other patients, at 48 ppb.
Atopic patients also had a lower FeNO threshold for eosinophilic asthma than non-atopic patients, at 49 versus 30 ppb, respectively, as did smokers compared with non-smokers, at 27 ppb versus 46 ppb.
Schleich and team conclude in the journal Thorax: "FeNO is able to identify the presence of sputum eosinophilia in unselected patients with asthma with reasonable accuracy as long as thresholds are adjusted for high doses of inhaled corticosteriods, atopy, and smoking status."
MedWire (www.medwire-news.md) is an independent clinical news service provided by Current Medicine Group, a trading division of Springer Healthcare Limited. © Springer Healthcare Ltd; 2010
By Mark Cowen