Blood tests may one day replace sleep studies for apnea

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

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.