The core criteria for a diagnosis of OSA are largely unchanged from ICSD-2. The diagnosis requires either signs/symptoms (eg, associated sleepiness, fatigue, insomnia, snoring, subjective nocturnal respiratory disturbance, or observed apnea) or associated medical or psychiatric disorder (ie, hypertension, coronary artery disease, atrial fibrillation, congestive heart failure, stroke, diabetes, cognitive dysfunction, or mood disorder) coupled with five or more predominantly obstructive respiratory events (obstructive and mixed apneas, hypopneas, or respiratory effort-related arousals, as defined by the AASM scoring manual) per hour of sleep during PSG. Alternatively, a frequency of obstructive respiratory events ≥ 15/h satisfies the criteria, even in the absence of associated symptoms or disorders. The most significant change from ICSD-2 is that a respiratory event index (based on hours of monitoring time) may be derived from out-of-center sleep testing (OCST). The same criterion frequencies of breathing disturbance apply when OCST is used, although OCST often underestimates frequency because recording time, rather than sleep time, becomes the denominator for calculation of the index.