Exhaled NO and exhaled breath condensate pH in the evaluation of asthma control

Asthma is a chronic inflammatory airways disorder. However, no biomarker of airways inflammation has been included in the assessment of asthma control.

To evaluate exhaled NO (FeNO) and exhaled breath condensate (EBC) pH in patients with asthma according to the level of control, and their performance in the identification of not well-controlled patients.

FeNO and EBC pH after Argon deaeration were measured in 274 consecutive patients. Asthma control was evaluated by two asthma specialists blinded to FeNO and pH measurements according to GINA guidelines, as well as by asthma control test (ACT) and asthma control questionnaire (ACQ).

FeNO was higher and EBC pH was lower in patients with not well-controlled compared to controlled asthma. In ROC analysis, FeNO presented an AUC of 0.790 for the identification of not well-controlled asthma performing better in non-smokers; EBC pH presented an AUC of 0.791 for the identification of not well-controlled asthma, performing better in smokers. The performance of both biomarkers was inferior to that of ACT and ACQ. FeNO values >30 ppb presented positive predictive values (PPV) > 0.85 with the exception of smokers treated with inhaled corticosteroids. EBC pH values ≤7.20 presented PPV >0.80 in all groups. The presence of FeNO >30 ppb and/or EBC pH ≤7.20 was indicative of not well-uncontrolled asthma in 88.3% of the patients.

FeNO and EBC pH levels may identify patients with not well-controlled asthma. However, their performance was inferior to clinical judgment and may be limited to selected subgroups of asthmatic patients.