Apnea-Hypopnea Index (AHI)

What is the apnea-hypopnea index?

The apnea-hypopnea index (AHI) is the average number of times you stop breathing (apneas) and have shallow breathing events (hypopneas) per hour of sleep.

It’s one way to diagnose and measure the severity of obstructive sleep apnea. Apneas and hypopneas are:

• Apneas. These are pauses in breathing. They last at least 10 seconds and will reduce your airflow.
• Hypopneas. This is a blockage of airflow that affects how well you breathe. With this event, you’re not breathing enough and it’s associated with a drop in oxygen levels in your blood.

Your brain constantly monitors your body’s status and adjusts your heart rate, blood pressure and breathing. When you have apnea or hypopnea, your brain reacts by triggering a reflex that wakes you up enough for you to breathe. Once you resume breathing, your brain allows you to go back to sleep. Most of these arousals are very subtle and you may not realize they’re happening.

AHI tracks how many times you have apnea and hypopnea events per hour. The more severe sleep apnea is, the more often these interruptions happen.

How is the apnea-hypopnea index calculated?

A sleep study is when your provider gathers this data to calculate the AHI. This is an overnight test that tracks and records how your body systems are working while you sleep. Sleep studies can be done in a sleep lab or at home. Home studies are simpler to do but data provided by these tests is limited.

Your healthcare provider will divide the total number of apneas and hypopneas by the total number of hours you slept to get your AHI score.

Apnea-hypopnea index severity

The American Academy of Sleep Medicine uses a range to categorize the severity of apnea and hypopnea events in adults:

• Mild: Five to fewer than 15 events per hour
• Moderate: 15 to fewer than 30 events per hour
• Severe: 30 or more events per hour

Your provider will use this calculation to determine the severity of sleep apnea.

What is a normal apnea-hypopnea index?

A normal apnea-hypopnea index for adults is fewer than five apnea and hypopnea events per hour. You don’t have a form of sleep apnea at this range.

Is the apnea-hypopnea index different for children?

Yes, the apnea-hypopnea index is different for children and adults. The pediatric AHI range is:

• Mild: One to fewer than five events per hour
• Moderate: Five to fewer than 10 events per hour
• Severe: 10 or more events per hour

A provider will make an obstructive sleep apnea diagnosis if your child has an AHI of one or above. A normal score is less than one for children. In some cases, a provider may use the adult scale for adolescents and teenagers.

What is a good AHI score on a CPAP machine?

The goal for adults receiving treatment for obstructive sleep apnea with a CPAP machine is below five. You and your healthcare provider will determine what score you should aim for. It’s usually a reduction from what you registered during a sleep study.

A CPAP machine can track your apnea-hypopnea index while you wear it. It detects changes to your breathing and uses this information to estimate your AHI score. It isn’t an exact measurement. But it can give your provider more information on how well treatment with the CPAP is working.

What are the drawbacks to the apnea-hypopnea index?

The AHI is a helpful tool, but it isn’t perfect on its own. Some of the drawbacks to this test may include:

• Mixed understanding of hypopnea. Many providers have a clear definition of apnea, but hypopnea’s definition has many factors like airflow and oxygen level reduction or frequent nighttime arousals.
• Limitations. AHI only measures apneas and hypopneas during sleep. It doesn’t provide any other information about how severe these events might be.
• Inaccurate results. Some at-home tests may provide less than accurate results.

While AHI may offer key insights into the type of rest you get at night, it only plays a role in determining the severity of a sleep disorder diagnosis. Your care team will use your AHI in addition to other test results to make an informed decision about your health.