Breath-based stratification of asthma severity using the MISTRAL platform with integrated H2S sensor and clinical validation.

Exhaled breath analysis offers a painless window into airway inflammation, yet its clinical adoption is limited by a shortage of robust biomarkers. Hydrogen sulfide ([Formula: see text]) has been detected in biological fluids, but its diagnostic value across asthma severities is not well established. In this study, we integrated an electrochemical [Formula: see text] sensor with a detection limit of 1 ppb into the MISTRAL platform. We evaluated exhaled [Formula: see text] in a prospective cohort of 28 adult asthmatic patients. Mean exhaled [Formula: see text] concentrations were significantly higher in individuals with mild-to-moderate asthma ([Formula: see text]) than in those with severe asthma ([Formula: see text]; one‑tailed t‑test [Formula: see text], [Formula: see text]). In early-stage disease, [Formula: see text] levels negatively correlated with maximal expiratory flow MEF[Formula: see text], with a similar trend for MEF[Formula: see text], whereas in severe asthma, positive but not fully statistically significant correlations emerged with FEV[Formula: see text]/FVC ratio, and vital capacity VC. These findings reveal a biphasic pattern: elevated [Formula: see text] may signify a compensatory antioxidant response that collapses as damage in the medium-to-peripheral airways progresses. The plug-and-play MISTRAL platform thus enables real-time, point-of-care assessment of exhaled [Formula: see text] as a promising, and complementary biomarker to FeNO and blood eosinophil count, offering a rapid, non-invasive indicator of disease control, treatment responsiveness, and exacerbation risk.