Predictors of obstructive sleep apnea syndrome in bronchial asthma patients: investigating the obesity–inflammation interplay through LEP, IL-6, and NLR

BACKGROUND: Bronchial asthma (BA) frequently coexists with obstructive sleep apnea syndrome (OSAS). The obesity-inflammation axis may underlie this overlap, but pragmatic predictors and biomarker utility remain incompletely defined. OBJECTIVE: To identify clinical predictors of OSAS in BA and evaluate the diagnostic performance of leptin (LEP), interleukin-6 (IL-6), and neutrophil-to-lymphocyte ratio (NLR), individually and in combination. MATERIALS AND METHODS: In a prospective study, 263 adults with BA were enrolled and classified into OSAS (n=124) and non-OSAS (n=139) groups by polysomnography. The OSAS group was stratified by apnea-hypopnea index (AHI) into mild (n=59), moderate (n=42), and severe (n=23). Clinical variables were compared with univariate tests. Independent predictors were identified using binary logistic regression. Serum LEP and IL-6 (immunoassays) and NLR (hematology) were measured. Biomarker-AHI relationships were assessed by Spearman's correlation. Diagnostic performance was evaluated using receiver operating characteristic (ROC) curves and DeLong's test. RESULTS: On univariate analysis, OSAS cases were older and more often male, with higher rates of obesity, severe BA, neck circumference >40 cm, rhinitis, and gastroesophageal reflux disease (GERD). Logistic regression confirmed obesity, severe BA, neck circumference >40 cm, rhinitis, and GERD as independent predictors. LEP, IL-6, and NLR were significantly higher in OSAS than non-OSAS and increased progressively across AHI strata. LEP correlated strongly with IL-6, IL-6 with NLR, and LEP with NLR to a lesser extent (all P