Written and medically reviewed by Kwaku Osafo-Mensah, MDPulmonary Medicine | Sleep Medicine | Diplomate, American Board of Sleep Medicine (ABSM)Medically reviewed: August 2026 Sleep-study reports contain an alphabet soup of abbreviations. Three of the most important are AHI, RDI, and REI. They are related measurements of sleep-disordered breathing, but they are not necessarily interchangeable. Understanding … Continue reading AHI vs. RDI vs. REI: What’s the Difference on a Sleep Study?