Diagnostic and Translational Values of Point-of-care Blood Eosinophils and Exhaled Nitric Oxide (FeNO) in People Referred by Primary Care for Suspected Asthma

BACKGROUND Asthma affects 10% of the general population but remains a diagnostic challenge. Considering the difficult access, weak specificity, and low clinical utility of bronchial provocation tests, more effective diagnostic methods are needed. Blood eosinophils and exhaled nitric oxide (FeNO) are biomarkers of type-2 inflammation that have established mechanistic, prognostic and theragnostic values in chronic asthma. Specifically, these biomarkers identify attack-prone patients with ongoing alarmin, type-2 cytokine, and chemokine signalling at the epithelial level driving airway hyperresponsiveness and accelerated lung function decline. Most importantly, these biomarkers also identify those who benefit the most from anti-inflammatory therapy. Considering the above clinical utilities, using biomarkers in primary care to diagnose airways disease in people with suspected asthma would represent a very effective diagnostic strategy. HYPOTHESIS: In people with non-diagnostic spirometry and asthma suspected by primary care, measuring blood eosinophils and FeNO is a feasible diagnostic strategy with good accuracy and the added value of early mechanistic insight in epithelial signalling pathways. OBJECTIVE: To estimate the diagnostic performance parameters of type-2 biomarkers in people with suspected asthma and a non-diagnostic spirometry. An exploratory analysis of inflammatory proteins (alarmin, type-2 cytokines, chemokines) in the nasal epithelial lining fluid (NELF) and serum according to biomarkers will be conducted. This and other secondary exploratory objectives will lead to better mechanistic and operational insight on the value of type-2 biomarkers in early disease. METHODS: The investigators propose a prospective observational study on the logistical feasibility, receiver operating characteristics (ROC), and mechanistic value of point-of-care type-2 inflammatory biomarkers to diagnose asthma (Figure). The study will include 123 people ≥18 years old with non-diagnostic pre-postbronchodilator spirometry referred by primary care for a methacholine challenge via the Suspected Asthma pathway of the Centre Hospitalier Universitaire de Sherbrooke. After the methacholine challenge, patients will complete questionnaires, have blood eosinophils measured (by venous blood sample), FeNO measured (by electroluminescence), nasosorption performed, and serum harvested for allergy testing and inflammatory protein measurement. OUTCOMES: The main analysis will be ROC plots of (1) FeNO alone; (2) blood eosinophils alone; and (3) the combination of blood eosinophils and FeNO;. The ROC plot will be based on a methacholine provocative dose ≤200 mcg (\~ provocative concentration ≤8 mg/mL). The target sample size of 123 will have 90% power to compute 3 ROC curves' area under the curve (AUC) ≥ 0.7 significantly different from the null hypothesis (AUC=0.5) with a conservatively corrected two-sided α error \< 0.016, assuming a positive/negative case ratio of 2. Secondary outcomes are the diagnostic and cost-effectiveness of blood eosinophil and FeNO measurement compared to methacholine challenges; and univariate plus multivariate modelling between blood eosinophils, FeNO, and inflammatory proteins (alarmins TSLP and IL-33; type-2 cytokines IL-4, -5, -13; chemokines eotaxin-3 and TARC) measured in the NELF and serum, or metabolites measured in the urine. EXPECTED RESULTS: It is expected that type-2 inflammometry to be a useful alternative diagnostic pathway with benefits extending beyond diagnostic accuracy thanks to early insight into the inflammatory phenotype. IMPACT: This observational study will support further validation studies and/or trials assessing biomarker-assisted diagnosis and management of asthma in the community setting. Measuring biomarkers at the time of diagnosis could facilitate a 'predict and prevent' approach to diagnostic algorithms in airway disease