What Is AHI? Sleep Apnoea Severity Explained
AHI, the apnoea-hypopnoea index, counts how many times your breathing pauses or shrinks per hour of sleep. The NHS grades it as mild (5 to 14), moderate (15 to 30) or severe (over 30). Only a clinical sleep study can produce an AHI. No phone app can measure it.
If you have seen “AHI” on a result, a leaflet or a guide and wondered what is AHI in plain terms, this page explains it. It is a clinical measure of sleep apnoea, and the bands tell you how severe a case is.
What is AHI and what does it stand for?
AHI stands for apnoea-hypopnoea index. It counts two kinds of breathing event per hour of sleep:
- An apnoea is a complete pause in breathing lasting 10 seconds or more.
- A hypopnoea is a partial reduction in breathing, also lasting 10 seconds or more.
Add both together, divide by the hours you slept, and you get your AHI. It comes from a sleep study that measures your breathing, oxygen and other signals through the night, not from a microphone listening to snoring.
What are the AHI severity bands?
The NHS and NICE use the same thresholds to grade obstructive sleep apnoea. Below 5 is considered normal.
| AHI (events per hour) | Severity |
|---|---|
| Under 5 | Normal |
| 5 to 14 | Mild |
| 15 to 30 | Moderate |
| Over 30 | Severe |
These are clinical bands. They are set and read by doctors, not by consumers or apps.
What about ODI and RDI?
You may see two related measures on a report:
- ODI (oxygen desaturation index) counts how many times your blood oxygen dips per hour. It is separate from AHI.
- RDI (respiratory disturbance index) adds breathing-effort arousals to the apnoeas and hypopnoeas, so it usually reads a little higher than AHI.
All three come from monitored sleep studies. In the UK, that usually starts with a home test (respiratory polygraphy), with a fuller in-lab study for unclear cases.
Can an app give me an AHI?
No. AHI requires measuring airflow and oxygen, which a phone cannot do from sound alone. Loud snoring tends to rise with apnoea severity, but it cannot confirm or rule it out. An app cannot diagnose sleep apnoea, and only a clinical sleep study can.
What a tracker can do is show patterns over time. Kip records and scores your snoring loudness and frequency on your iPhone, so you can see trends across a week and bring real notes to your GP. It is a wellness tool, not a medical device, and it never measures blood oxygen or AHI.
If the snoring comes with breathing pauses, gasping or daytime exhaustion, that is worth a conversation. See the difference between snoring and sleep apnoea, check the signs worth raising, or read about home sleep apnoea tests.
Sources
- NHS: Sleep apnoea
- NICE NG202: Terms used in this guideline
- Sleep Foundation: Apnea-Hypopnea Index (AHI)
FAQ
What is a normal AHI?
An AHI below 5 events per hour is considered normal. From 5 to 14 is graded mild, 15 to 30 is moderate, and over 30 is severe. These bands come from a clinical sleep study, not from a home gadget or app.
Can a snoring app measure my AHI?
No. AHI needs measurements of airflow and blood oxygen that a phone cannot take from sound. Apps can track snoring loudness and frequency, which may flag patterns consistent with disrupted sleep, but they cannot produce an AHI. Only a clinical sleep study can.
Is a high AHI dangerous?
A higher AHI means more frequent breathing events, and untreated sleep apnoea is linked to problems like high blood pressure over time. The figure itself is not a verdict you should act on alone. If you have been given an AHI or suspect sleep apnoea, discuss it with your GP, who can arrange the right assessment and care.