A Medicare-approved doctor must document an OSA diagnosis through a sleep study. To qualify for a three-month CPAP therapy trial, you must have an AHI or RDI of at least 15 events per hour, or five to 14 events per hour combined with other documented symptoms (like heart disease, hypertension, or excessive daytime sleepiness). Your doctor must document your CPAP therapy adherence and confirm its effectiveness for you to qualify for a 13-month CPAP equipment rental (and ultimate purchase).