Objective: To examine whether circulating leptin levels correlate with the severity of disease in patients with obstructive sleep apnea. Design: Prospective nonrandomized study. Setting: Referral sleep laboratory for patients with sleep-disordered breathing and biochemistry laboratory. Patients: Thirty-two subjects (mean+/-SD age 47+/-12 years) who were referred for suspected sleep apnea underwent an overnight sleep study and fasting morning venous blood sampling. Patients were divided into 3 ...