When my sleep study came back in 2011, my AHI was 89.2. I had no idea what that meant. My sleep doctor said it was the worst case seen in 14 years of practice.
That one number decides a lot. It tells your doctor how serious your sleep apnea is. Once you are on CPAP, it tells you whether the therapy is working. This page explains it in plain English. I'm not a doctor, so talk to your sleep specialist about your own results.
What is AHI?
AHI stands for apnea-hypopnea index. It is the number of times you stop breathing, or nearly stop, in an average hour of sleep.
- An apnea is when your breathing stops for 10 seconds or more.
- A hypopnea is when your breathing gets very shallow for 10 seconds or more. It counts when it lowers your oxygen or briefly wakes you.
Both count the same in your AHI. A lower number is better.
How AHI is calculated
The sum is simple. Add up both kinds of events, then divide by the hours you slept.
AHI = (apneas + hypopneas) ÷ hours of sleep
Say your sleep study counted 40 apneas and 50 hypopneas over 6 hours of sleep. That is 90 events divided by 6 hours, for an AHI of 15.0. On the chart below, that is moderate sleep apnea.
Many home sleep tests report an REI (respiratory event index) instead. It divides by the hours the test was recording, not the hours you were asleep. Awake time pulls the number down a little, so REI can read lower than AHI.
What is a good AHI score?
It depends on whether you are being tested or already treated. The same number means different things.
AHI chart for a sleep study (before treatment)
These are the adult ranges from the American Academy of Sleep Medicine (AASM).
| AHI | Sleep apnea severity |
|---|---|
| Under 5 | Normal |
| 5 to 14.9 | Mild |
| 15 to 29.9 | Moderate |
| 30 or more | Severe |
A good AHI on CPAP
Once you are on CPAP, the goal is under 5. That is the target the AASM sets when a sleep lab picks your pressure. Your doctor may set a different goal for you.
| AHI | What it means on CPAP |
|---|---|
| Under 5 | On target |
| 5 to 9.9 | Above target |
| 10 or more | Well above target |
One bad night is normal. Look at your average over a week. That tells you far more than any single morning.
How to lower your AHI
If your number on CPAP is creeping up, start with these. Most of them come down to air getting out where it should not.
Stop the leaks
A leaking mask lets air pressure escape. Your machine cannot hold your airway open as well. Here is why CPAP masks leak and how to fix it.
Keep your mouth closed
If you use a nasal mask or nasal pillows and your mouth falls open, air rushes out. A chin strap can help. So can a full face mask.
Replace worn parts on time
A cushion that has gone soft will not seal. Use the supply replacement schedule to see if yours is overdue.
Watch your sleep position and evening drinks
Many people have more events sleeping on their back. Alcohol close to bedtime relaxes the muscles in your throat. Both can push your number up.
Ask about your pressure
Your needs can change over time. Only your doctor should change your settings. Some people do better on a machine that adjusts itself. Read about CPAP vs BiPAP vs APAP.
Mention central apneas
Some apps split events into types. If many are marked "central" or "clear airway," tell your doctor. More pressure does not fix those, and they need a different look.
Your next step
Open your CPAP app and find your average AHI for the last 7 nights. Put it in the calculator above. If it is 5 or higher, call your sleep doctor and ask whether your settings need a check.
If your mask is the problem and your supplier will not help with a refit, find a CPAP supplier near you.
CPAPLocator.com is a directory service only. We are not a medical provider. Content is for informational purposes only. Always consult your healthcare provider.