> ## Documentation Index
> Fetch the complete documentation index at: https://help.apnealytics.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Understanding AHI

> What the Apnea-Hypopnea Index measures, the GREAT / MILD / MODERATE / HIGH bands, the sub-indices behind the number, and why machine AHI is for tracking trends, not diagnosis.

**AHI — the Apnea-Hypopnea Index — is the average number of breathing events per
hour of use.** It's the headline number your machine reports each night and the
one clinicians watch most. Apnealytics charts it over time and breaks it down so
you can see not just *how many* events, but *what kind*.

> [!WARNING]
>
> Machine-estimated AHI is **not** the same as a diagnostic sleep study. It's
> excellent for tracking trends over time, not for diagnosing or grading disease.
> Bring the trends to your clinician rather than self-diagnosing from them.
> Apnealytics is a tracking and coaching tool, not a medical device.

## The bands

On therapy, most people aim for an AHI **under 5**. Apnealytics bands each night
so a glance tells you where it sits:

| Band | AHI (events/hour) | What it generally means |
| - | - | - |
| **GREAT** | under 5 | Well-controlled on therapy |
| **MILD** | 5–15 | Mild |
| **MODERATE** | 15–30 | Moderate |
| **HIGH** | above 30 | Severe |

> [!NOTE]
>
> A single high night is usually just noise. A **sustained shift** over many nights
> is what's worth a conversation with your clinician.

## The event types behind the number

Your machine estimates several kinds of event and adds them up into AHI.
Apnealytics splits them out so two nights with the same AHI but different make-ups
look different:

> [accordion] OAI — obstructive apneas
>
> The airway physically collapses and blocks airflow. The obstructive apnea
> index (OAI) counts these per hour.

> [accordion] CAI — central apneas
>
> The brain briefly stops sending the signal to breathe, so there's no effort
> to breathe at all. The central apnea index (CAI) counts these per hour.

> [accordion] HI — hypopneas
>
> Partial narrowings that reduce — but don't fully stop — airflow. The
> hypopnea index (HI) counts these per hour.

> [accordion] UAI — unclassified events
>
> Events the machine couldn't confidently sort into the categories above. The
> unclassified apnea index (UAI) captures these.

Apnealytics breaks AHI into these components on the Explore views, so you can see
whether a change in your number is coming from obstructive events, central events,
or hypopneas.

## Read leak first

Before reading events on any night, glance at the **leak**. A high-leak stretch
makes AHI unreliable, because air escaping the mask distorts what the machine can
measure. If a night's AHI looks surprising, check whether leak was high that
night — see [Metrics explained](https://help.apnealytics.com/guides/metrics-explained.md).

> [!TIP]
>
> The in-app Knowledge Hub article "Understanding Your AHI" covers this in a
> three-minute read, and every page that interprets numbers carries the
> not-a-diagnosis reminder.


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