Exhaled nitric oxide and asthma control: a longitudinal study in unselected patients

Controlled studies have shown that monitoring of the exhaled nitric oxide fraction (F(eNO)) improves asthma management. However, the studies seldom consider the full range of patients seen in clinical practise. In the present study, the ability of F(eNO) to reflect asthma control over time is investigated in a regular clinical setting, and meaningful F(eNO) cut-off points and changes are identified. Answers to the Asthma Control Questionnaire and F(eNO) were recorded at least once in 341 unselected asthma patients. The whole population and subgroups were considered, i.e. both inhaled corticosteroid (ICS)-naïve and low or high-to-medium (500 mug beclomethasone dipropionate equivalents.day(-1)) ICS-dose groups. An F(eNO) decrease <40% or increase <30% precludes asthma control optimisation or deterioration, respectively (negative predictive value 79 and 82%, respectively). In the present study's low-dose group, a decrease >40% indicated asthma control optimisation (positive predictive value (PPV) 83%). In ICS-naïve patients, F(eNO) >35 ppb predicted asthma control improvement in response to ICS (PPV 68%). In most cases, forced expiratory volume in one second assessments were not useful. In conclusion, in a given patient, exhaled nitric oxide fraction was found to be significantly related to asthma control over time. The overall ability of exhaled nitric oxide fraction to reflect asthma control was reduced in patients using high doses of inhaled corticosteroids. Forced expiratory volume in one second had little additional value in assessing asthma control.