<b>Introduction:</b> Clinical trial evidence shows that biologic efficacy for severe asthma is related to biomarkers, but the extent to which this can be used to select treatments in the real-world is unclear. <b>Aims and Objectives:</b> We aimed to determine if pre-biologic measurements of biomarkers were predictive of lung function and asthma control in severe asthma patients treated with anti-IL5/5R or anti-IgE biologics in real- world settings. <b>Methods:</b> The International Severe Asthma Registry collects data from 23 countries. We included all patients aged ≥18 years with data on blood eosinophil count (BEC), fractional exhaled nitric oxide (FeNO) or serum immunoglobulin-E (IgE) and with pre- and post-biologic FEV 1 and asthma control. Associations between outcomes one year after biologic initiation and highest pre-biologic biomarker levels were examined using regression models, adjusting for baseline measurement of the relevant outcome. <b>Results:</b> Higher baseline BEC and FeNO were associated with greater post-treatment FEV 1 improvement in anti-IgE and anti-IL5/5R patients, and reduced odds of uncontrolled asthma in anti-IL5/5R patients (Figure). IgE level was not associated with either of these outcomes. A combination of BEC and FeNO predicted follow-up FEV 1 improvement more accurately than either alone (p<0.01). <b>Conclusions:</b> The results support the use of BEC and FeNO to help to identify patients who will benefit most from biologics.
