Association Between Serum Leptin Concentrations and Disease Severity Across Airway Disease Phenotypes: A Single-Center Retrospective Observational Study

Background/Objectives: Leptin is a pleiotropic adipokine linking energy metabolism with innate and adaptive immunity. Its relationship with clinical severity across distinct airway disease phenotypes remains insufficiently characterized. This study examined serum leptin concentrations in adults with allergic rhinitis, non-allergic asthma, and allergic asthma associated with allergic rhinitis. Methods: This single-center retrospective observational study analyzed fully anonymized clinical and laboratory data from 88 adults: patients with allergic rhinitis (n = 31), non-allergic asthma (n = 15), or allergic asthma with allergic rhinitis (n = 22) and healthy controls (n = 20). Serum leptin was measured using a quantitative sandwich enzyme-linked immunosorbent assay. Disease severity was classified using the Allergic Rhinitis and its Impact on Asthma and Global Initiative for Asthma frameworks applicable during the study period. Statistical analyses were performed using IBM SPSS Statistics, version 26.0 (IBM Corp., Armonk, NY, USA), and available original statistical outputs were summarized using retained t statistics and two-sided p values. Results: Stage-specific mean serum leptin concentrations were heterogeneous and non-monotonic. Statistically significant relationships between leptin concentration and disease stage were reported for allergic rhinitis (t = 2.844; p = 0.008), non-allergic asthma (t = 4.240; p = 0.001), and allergic asthma with allergic rhinitis (t = 2.700; p = 0.013). In the allergic rhinitis subgroup, 64.5% of participants had normal weight, 32.3% were overweight, and 3.2% had grade II obesity; weight category was not significantly related to rhinitis stage. Conclusions: The retained analyses indicate statistically significant relationships between serum leptin concentration and clinical disease stage across the investigated airway phenotypes. However, the stage-specific descriptive means were heterogeneous and non-monotonic and therefore do not support a uniform progressive increase in leptin with increasing disease severity. Because complete model outputs and covariate-adjusted estimates were unavailable, these findings should be regarded as exploratory and require prospective validation with appropriate adjustment for adiposity and other relevant metabolic confounders.