AHI stands for apnea-hypopnea index. It's the number of times an hour your breathing stopped or became very shallow while you slept. Your CPAP machine counts these events through the night, then divides by the hours you used it.
So an AHI of 3.0 means that, on average, your breathing paused or became shallow 3 times an hour. A night of 7 hours with 21 events works out to exactly 3.0.
What it counts
- Apneas: your airflow stops for 10 seconds or more.
- Hypopneas: your airflow is reduced, but not stopped, for 10 seconds or more, so your breathing becomes shallow.
Both kinds of event count toward AHI. Our guide to what the events meanexplains the different types your machine flags.
What the ranges mean
Doctors use these ranges, for adults, when they diagnose sleep apnea with a sleep study:
| AHI | Meaning |
|---|---|
| Under 5 | Normal |
| 5 to 15 | Mild sleep apnea |
| 15 to 30 | Moderate sleep apnea |
| 30 or more | Severe sleep apnea |
On treatment, the number your machine reports is your residual AHI: what's left with CPAP working. Many people see it fall from their diagnosis number into the low single figures. Many clinicians look for an AHI under 5 on treatment, but your own goal is for your clinician to set. CPAPGeeks colors each night green under 5, amber from 5 to just under 15 and red from 15 to make it easy to scan.
Why one night isn't the whole story
AHI moves around from night to night. A single high night is common and usually explained by something simple:
- A short night. Two events in one hour is an AHI of 2; the same two events in a 20-minute nap is an AHI of 6.
- Mask leak. A leaking mask can't hold the pressure that keeps your airway open. See why masks leak.
- Sleeping on your back, alcohol, or a cold. All of these can make the airway more likely to collapse.
Look at the trend across a week or a month, not one night. If your AHI stays high, or your sleepiness comes back, take your numbers to your sleep clinician. Don't change your machine's settings yourself.
Machine AHI versus a sleep study
Your machine estimates events from airflow alone. A sleep study also measures brain waves, oxygen and breathing effort, so it's more precise. Machine AHI is very good for spotting trends at home, but the two numbers won't always match exactly.