You have a sleep study report with a lot of numbers, and the one everyone talks about is the AHI. This guide explains what it measures, what the severity bands mean, what the other numbers on the report tell you, and what usually happens next.
AHI stands for apnoea-hypopnoea index. It is the number of breathing events during sleep divided by the number of hours you slept, so it is expressed as events per hour.
A pause in breathing during sleep, where airflow stops or falls very sharply for at least 10 seconds.
A partial reduction in airflow lasting at least 10 seconds, usually with a drop in blood oxygen or a brief waking (arousal) from sleep.
For adults, sleep apnoea severity is usually grouped like this:
Generally considered normal.
Mild obstructive sleep apnoea.
Moderate obstructive sleep apnoea.
Severe obstructive sleep apnoea.
The lowest oxygen reading, the time spent below a set level such as 90%, and the ODI (how often oxygen dips per hour). Long or deep dips can matter even when the AHI looks moderate.
How often you briefly wake or lighten your sleep per hour. A high value can explain daytime tiredness even without many obvious breathing events.
How much time you spent in light sleep, deep sleep and REM sleep, and how much of your time in bed was actually spent asleep.
Many people have more events lying on their back or during REM sleep. This can guide treatment choices, for example whether position matters.
Periodic limb movements during sleep may be reported. Their importance depends on whether they are waking you and on your symptoms.
Two people with the same AHI can need very different care. What matters is the number together with your symptoms and health.
The next step depends on the result and on you. It may be reassurance, a repeat or different test, or treatment. Options for sleep apnoea can include weight and lifestyle measures, positional strategies, CPAP or other PAP therapy, an oral appliance, or an ENT assessment.
CPAP is commonly considered for moderate to severe sleep apnoea, and sometimes for mild disease when symptoms or related conditions are present. It is not automatic. If you already use CPAP, see our page on CPAP and PAP therapy. For the wider picture of the condition, see sleep apnoea and snoring.
In adults, an AHI below 5 events per hour is generally considered normal. In children, much lower thresholds are used, and an AHI of 1 or more per hour may be considered abnormal, so adult cut-offs should not be applied to a child's report.
Yes. Sleep position, alcohol, sedating medicines, nasal congestion and how much REM sleep you get can all change the number. A first night in a sleep lab can also differ from a usual night at home.
AHI counts apneas and hypopneas per hour. RDI (respiratory disturbance index) also includes subtler breathing-effort events. ODI (oxygen desaturation index) counts how often blood oxygen drops by a set amount per hour.
No. CPAP is commonly considered for moderate to severe sleep apnoea, and sometimes for mild disease when there are symptoms or related health conditions. Other options may suit some people. The decision is made together after a clinical assessment.
Yes. In an online Sleep Medicine consultation, your PSG or home sleep test report can be reviewed alongside your symptoms and medical history, and next steps can be discussed.
Bring your report and your symptoms to an online Sleep Medicine consultation, and the findings can be reviewed in the right clinical context.