Interrelationships between body mass, oxygen desaturation, and apnea-hypopnea indices in a sleep clinic population.

STUDY
OBJECTIVES: To investigate the relationship between oxygen desaturation index (ODI), body mass index (BMI), and apnea-hypopnea index (AHI) in a large sleep clinic population.
DESIGN: Retrospective observational.
SETTING: Sleep disorders clinic. PATIENTS OR PARTICIPANTS: 11,448 individuals undergoing diagnostic polysomnography (PSG) at a sleep disorders clinic. MEASUREMENTS AND
RESULTS: Polysomnography were scored using Chicago criteria. ODI at 2%, 3%, and 4% threshold levels were derived. The study population was subdivided into BMI categories in steps of 5 kg/m(2). Mean ODI and the accuracy of ODI for detecting an AHI ≥ 15 (moderate-severe OSA) or ≥ 30 (severe OSA) were examined by BMI category, using the area under the curve (AUC) of receiver operator characteristic (ROC) curves for the 3 ODI thresholds. Based on AUC, ODI-3% performed best overall, achieving a significantly higher AUC than ODI-2% and ODI-4% for the diagnosis of moderate-severe OSA, and a higher AUC than ODI-2% for the diagnosis of severe OSA. When examining the effect of BMI, ODI-3% achieved a significantly higher AUC than ODI-2% in all BMI categories, and ODI-4% in non-obese subjects. The sensitivity of ODI for detecting OSA increased with BMI, while specificity decreased.
CONCLUSIONS: ODI-3% performed best overall, and when combined with appropriate clinical assessment, could be considered as an initial diagnostic test for OSA. OSA is more frequently associated with oxygen desaturation in obese subjects. BMI influences the accuracy of ODI for the diagnosis of OSA, and ODI should not be used in isolation as a test for OSA in subjects with a BMI below 25kg/m(2).