Identification of Biomarkers of Obstructive Sleep Apnea.

Inclusion Criteria: 1. Participants with obstructive sleep apnea (OSA): * Age 18 to 65 years. * Moderate or severe obstructive sleep apnea confirmed by overnight polysomnography (apnea-hypopnea index \[AHI\] ≥15 events/hour). * Willing and able to provide written informed consent. * Willing to undergo repeated blood sampling and study assessments. * Willing to use positive airway pressure (PAP) therapy and accept random assignment to immediate or delayed treatment. 2. Control participants: * Age 18 to 65 years. * No obstructive sleep apnea (AHI \<5 events/hour on overnight polysomnography). * Willing and able to provide written informed consent. * Willing to undergo study assessments and blood sampling. Exclusion Criteria: * Mild obstructive sleep apnea (AHI 5 to \<15 events/hour). * Central sleep apnea. * Previous treatment for obstructive sleep apnea within the previous 3 months. * Body mass index (BMI) ≥40 kg/m². * Severe cardiovascular disease. * Severe kidney disease or impaired renal function. * Significant liver disease. * Chronic inflammatory, autoimmune, or rheumatic disease. * Active cancer or other condition associated with systemic inflammation. * Chronic respiratory diseases, including asthma or chronic obstructive pulmonary disease. * Respiratory infection within 4 weeks before enrollment. * Major surgery or significant injury within the previous 3 months. * Chronic rhinosinusitis. * Current treatment with systemic corticosteroids, immunosuppressive drugs, cytotoxic drugs, chronic anti-inflammatory medications, or other medications that may influence inflammatory biomarkers. * Pregnancy or any condition that, in the opinion of the investigators, would make participation unsafe or interfere with interpretation of the study results.