B29-23 Maximal Mid-expiratory Flow as a Predictive Marker for Asthma in Young Adults

Rationale Asthma is common, though delays in diagnosis are not unusual resulting in an unnecessary decrease in functional capacity and quality of life. It has been suggested that the prevalence of small airways dysfunction (SAD) across all degrees of asthma severity is 50-60%; to date there have been few studies evaluating whether isolated SAD could be implicated as a precursor to classic asthma. Methods We conducted a single-center retrospective longitudinal study identifying young adults (18-39 years old) without preexisting lung disease who underwent spirometry and were found to have an isolated reduction in maximum mid-expiratory flow (MMEF) as determined either by 1) FEF25-75% below the LLN, 2) a positive FEF25-75% bronchodilator response or 3) both, all in the absence of classic obstructive lung disease. We followed these patients using electronic medical record review for a minimum of one year and compared this population to similarly aged patients with normal spirometry findings. The primary outcome was a future diagnosis of asthma. Secondary outcomes included time to asthma diagnosis, method of diagnosis as well as observational findings on relevant aspects of clinical management. Results We identified 73 patients in our intervention group who met criteria for isolated SAD. 150 patients with normal spirometry served as a control group. 27/73 patients (36%) in the intervention group were ultimately diagnosed with asthma compared to 4/150 patients (2.7%) in the control group (p < 0.0001). The median time to diagnosis in the intervention group was 6.2 months and 31.5 months in the control group. 44% of patients in the SAD group were prescribed an inhaler empirically, 64.4% of which included inhaled corticosteroids (ICS). 14/73 (19%) of patients in the SAD group had repeat spirometry performed, compared to 19/150 (12%) in the control group. Conclusion In this retrospective study, young adult patients with isolated SAD on spirometry in the absence of true obstruction were statistically more likely to be diagnosed with classic asthma in the future compared to similarly aged patients with normal spirometry. These patients were typically treated empirically with a varied inhaler regimen that frequently included an ICS. This study demonstrates that isolated SAD in young patients undergoing spirometry may be a key early finding in asthma prior to classic reversible obstructive lung disease. Clinical uncertainty was noted managing patients with this finding based on a varied approach to treatment and monitoring. Further studies evaluating the association between SAD and asthma are warranted. This abstract is funded by: None