Exploring the long-term utility of remotely monitored FeNO suppression testing in severe asthma

Confirmation of optimal inhaled corticosteroid use is essential before initiating biologic therapy. Fractional exhaled nitric oxide (FeNO) suppression testing (FeNOSuppT) is a proven phenotyping technique; however, its long-term effect on clinical outcomes remains unclear. To assess the real-world feasibility of delivering FeNOSuppT alongside digital inhaler monitoring and to examine its effect on biologic initiation and clinical outcomes. Prospective cohort study within 7 U.K. severe asthma centers. Patients received a sensor-enabled inhaled corticosteroid/long-acting β-agonist (ICS/LABA) inhaler during an initial appointment between July 2020 and June 2022. A positive FeNOSuppT was defined as greater than 42% FeNO reduction at short-term follow-up (typically 1-3 mo postbaseline). Biologic initiation and clinical outcomes were compared at short-term and long-term (typically 12 mo postbaseline) follow-up. Of 353 included patients, 257 (72.8%) completed the FeNOSuppT and 140 (54.5%) were positive. A positive FeNOSuppT was associated with greater improvements in the % predicted short-term forced expiratory volume in 1 second (FEV1%; 8.6% vs -0.3; P < .001) and the 6-Item Asthma Control Questionnaire (ACQ6; 0.7 vs 0.3; P = .001) compared with a negative test. Of 168 patients eligible for biologics who completed the FeNOSuppT, those with a positive result initiated biologics less often (48.2% vs 65.2%; P = .035). Despite this, there was a greater improvement in FEV1 (11.0% vs 2.3%; P = .016), and a similar reduction in both asthma symptoms (ACQ6 0.7 vs 0.8; P = .623) and exacerbations (66.7% vs 66.7%; P = .349) at long-term follow-up when compared with those with a negative FeNOSuppT. Delivering FeNOSuppT aligned with digital monitoring is feasible within routine care. A positive FeNOSuppT was associated with lower rates of biologic initiation, with similar clinical outcomes.