AHI sleep apnea index explained | VivaRespire

The AHI - Apnea-Hypopnea Index: Everything You Need to Know

The AHI is the central measurement in sleep apnea diagnosis. It is the number your doctor will use to assess the severity of your apnea and decide on treatment. Here is a clear explanation of what it means, how it is calculated, and why it matters.

What is the AHI?

The AHI (Apnea-Hypopnea Index) measures the average number of apneas and hypopneas occurring per hour of sleep.

An apnea: complete cessation of breathing for at least 10 seconds, caused by airway collapse (obstructive) or a brain signaling failure (central).
A hypopnea: partial reduction in airflow (≥ 30%) for at least 10 seconds, associated with an oxygen desaturation (≥ 3%) or a brain micro-arousal.

Simple example: if you sleep 8 hours and 120 apneas and hypopneas are recorded in total, your AHI is 120 ÷ 8 = 15/hour.

AHI severity thresholds

AHI (adult ≥ 16 years)	Severity	Clinical interpretation
< 5 /hour	Normal	No significant apnea
5 to 15 /hour	Mild apnea	Treatment based on symptoms and cardiovascular risk profile
15 to 30 /hour	Moderate apnea	Treatment recommended (CPAP or alternative)
> 30 /hour	Severe apnea	Urgent treatment required

In Belgium, the INAMI/RIZIV CPAP convention is accessible from IAHO ≥ 15/hour, or ≥ 5/hour with significant associated symptoms. For details on the convention: CPAP reimbursement in Belgium.

Difference between AHI and IAHO

AHI (Apnea-Hypopnea Index): the generic international term, counting all apneas and hypopneas (obstructive and central).
IAHO: the specific term used in Belgian INAMI nomenclature. It counts only obstructive apneas and hypopneas. This is the official criterion used for coverage decisions.

In everyday practice, AHI and IAHO are often used interchangeably for obstructive sleep apnea, which represents the vast majority of cases.

How is the AHI calculated?

Ambulatory polygraphy (at home): records airflow, thoracic movements, SpO2 and heart rate. Automatically calculates the AHI over recording time.
Polysomnography (in a sleep center): more comprehensive. AHI is calculated over actual sleep time (excluding waking periods). This is the gold standard.

Clinical importance of AHI

The AHI is never read in isolation. An AHI of 8/hour with disabling daytime sleepiness and hypertension may justify treatment, while an AHI of 12/hour in a totally asymptomatic patient may simply be monitored. Treatment decisions always integrate: AHI value, symptom severity, cardiovascular risk profile, and profession (commercial drivers, pilots).

Residual AHI on CPAP

Residual AHI	Interpretation
< 2 /hour	Excellent treatment
2 to 5 /hour	Satisfactory treatment
5 to 10 /hour	Partial - adjustment recommended (mask, pressure)
> 10 /hour	Medical reassessment needed

AHI in children: a different threshold

In children under 16, an IAHO ≥ 1/hour is considered abnormal and may justify treatment. Pediatric apnea is often caused by enlarged tonsils or adenoids, and the first-line treatment is usually surgical before considering CPAP.

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