Exploring the Long-Term Utility of Remotely Monitored FeNO Suppression Testing in Severe Asthma

Abstract

BACKGROUND: 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. OBJECTIVES: To assess the real-world feasibility of delivering FeNOSuppT alongside digital inhaler monitoring and to examine its effect on biologic initiation and clinical outcomes. METHODS: Prospective cohort study within 7 U.K. severe asthma centers. Patients received a sensor-enabled inhaled corticosteroid/long-acting ß-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. RESULTS: 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 (FEV(1)%; 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 FEV(1) (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. CONCLUSIONS: 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.