What Does Your AHI Score Mean? Breaking Down Sleep Apnea Severity

AHI is one of the measures used to diagnose sleep apnea, but it's not the only factor. Sleep specialists also consider oxygen levels, symptoms and overall health.²³

What is the apnea-hypopnea index (AHI)?

AHI refers to the average sleep apnea events per hour during a sleep study. These events are known as apneas or hypopneas:  

• During apneas, airflow stops for 10 or more seconds. The upper airways completely collapse, stopping air from getting to the lungs.

• During hypopneas, airflow is reduced for 10 or more seconds, causing shallow breathing. Hypopneas result from partial airway blockages.

Dr. Christian Guilleminault, a University of Stanford researcher, pioneered early sleep apnea research. In the late 1970s, he and his colleagues developed an apnea index (AI) to help diagnose sleep apnea and its severity. AI counted the number of apneas, or complete pauses, per hour of sleep.¹ Researchers later refined this metric to reflect the importance of hypopneas, renaming it the apnea-hypopnea index.

The relationship between AHI and sleep apnea types

Sleep apnea may be diagnosed if an AHI score indicates five or more breathing interruptions per hour, lasting more than 10 seconds each.³ The type of sleep apnea a person is diagnosed with depends on why breathing stops.

• Obstructive sleep apnea (OSA) is a condition where your upper airway becomes blocked many times while you sleep. This blockage can reduce or completely stop the flow of air. OSA is the most common type of sleep apnea. ³

• Central sleep apnea (CSA) is less common and occurs when the brain doesn't send signals to the muscles that control breathing. With central sleep apnea, most breathing pauses happen because the body “forgets" to breathe, not because something is blocking the airway.⁴

• Complex sleep apnea (CompSA) also called treatment-emergent CSA (TECSA) occurs when a person present both obstructive and central apneas. In this case, central apneas persist or emerge with CPAP treatment.

Sleep apnea severity chart

The apnea-hypopnea index (AHI) is calculated by dividing the total number of times breathing slows down or stops (apneas and hypopneas) during sleep by the total hours of sleep time. The score reflects the average number of respiratory events per hour of sleep and helps classify the severity of sleep apnea.

 Sleep Apnea Severity                      AHI (Events per hour)

These sleep apnea ranges apply only to adults. Typically, an AHI of less than 1.5 is considered normal in children.⁵
While the sleep apnea chart applies to men and women, research suggests women have lower AHI scores and shorter breathing pauses than men.⁶ This difference could result in underdiagnoses of sleep apnea among women.

How is AHI interpreted?

When interpreting sleep apnea results, it's important to understand how metrics such as AHI are collected and measured.

How sleep studies measure AHI

A sleep study is more than just a tool for diagnosing sleep apnea — it paints a better picture of your health by collecting information like oxygen levels, heart rate, brain waves and breathing patterns as you sleep.

Sleep studies, also referred to as sleep tests, can be done in different ways, depending on what your doctor thinks is best. Your doctor may recommend an in-lab sleep study if you have a more complex medical history and may benefit from comprehensive sleep monitoring. These types of sleep tests are usually conducted overnight in a lab, where a trained lab technician can monitor your sleep.²⁵ Another option your doctor may choose is a Home Sleep Test or HST. The HST collects data while you sleep and sends the information to your doctor.

In-lab sleep study

An in-lab sleep study, also known as polysomnogram (PSG), is a detailed test that records brain waves, blood oxygen levels, heart rate, breath rate, and eye and leg movements to measure how many times per hour you either stop breathing or have shallow breathing, and diagnose sleep disorders. Your doctor may recommend an in-lab sleep study if you have a more complex medical history and may benefit from comprehensive sleep monitoring. PSGs are usually conducted overnight in a sleep lab, where a trained lab technician can monitor your sleep.⁷

Home sleep test (HST)

An HST can be completed from the comfort of your own bed. A Home Sleep Test measures your oxygen saturation (the amount of oxygen in your blood), heart rate, and airflow, as well as the movements of your chest and abdomen and your position while you sleep to determine how many times per hour you either stop breathing or have shallow breathing. In fact, 60% to 70% of sleep studies are done using home-based tests.⁸

HSTs accurately diagnose moderate to severe obstructive sleep apnea about 90% of the time.⁹ Your doctor may recommend a home sleep test if you’re showing symptoms of a sleep disorder and have not been diagnosed with any other chronic medical conditions.

Beyond AHI: Complementary metrics

A sleep study can do more than diagnose a sleep condition. It can also help you learn more about your body. Sleep study test results may also include additional metrics:

• Oxygen desaturation index (ODI), which measures the average number of times oxygen blood levels drop below normal during one hour of sleep. While AHI counts the number of times respiratory events happen, ¹⁰ ODI can helps you and your doctor understand how a respiratory event affects your body.

• Respiratory disturbance index (RDI), which is the total number of apneas, hypopneas and other respiratory events experienced during an average hour of sleep. Unlike AHI, RDI includes breathing problems that are not categorised as apneas or hypopneas, which can also affect sleep quality.

• Arousal index, which is the average number of times you wake up, even briefly, during an hour of sleep. These awakenings can lead to fragmented sleep.

• Sleep position, which can also affect AHI measurements. The upper airway tends to collapse more when lying on the back,⁹¹¹ which can cause lead to more breathing interruptions and a higher AHI score .¹²

Understanding AHI results

While the apnea-hypopnea index (AHI) helps classify sleep apnea severity, diagnosis and treatment should always be guided by a doctor.

AHI has limitations.¹³ It tells you the number of apneas and hypopneas experienced, but not how long the events last, the impact on heart rate and oxygen levels, and how intense awakenings are. Scores may also change between sleep stages and body positions.

To figure out the next steps, a doctor will typically look at the big picture. They consider AHI along with:

• Symptoms

• Overall health and medical history

• ODI, RDI and other metrics

• Nightly changes in AHI scores

Using AHI s to treat and monitor sleep apnea

The sleep apnea rating scale can help doctors develop a treatment plan, monitor its effectiveness and adjust treatment approaches if needed.

Using AHI to determine treatment

Sleep apnea treatment options depend in part on AHI scores. In general:

• Oral appliances may be an option for mild to moderate OSA.¹⁸

• Continuous positive airway pressure (CPAP) therapy is the gold standard for patients with moderate to severe obstructive sleep apnea. ²⁶

• Surgery may be considered if other treatments don't work.⁹

• Lifestyle changes such as losing weight, adjusting sleeping position and quitting smoking may also be recommended to help reduce sleep apnea symptoms.²²

Each person’s sleep apnea treatment is personalised, ¹⁶ and your doctor will help determine treatment options for you. Even mild cases of OSA deserve attention, especially if there are underlying health conditions or symptoms that interfere with daily life.

AHI is also used by insurance companies to determine treatment coverage. Policies vary and coverage usually depends on how the sleep study defined a hypopnea.¹⁴

How treatment impacts AHI

Sleep apnea treatments aim to lower AHI to healthier levels. Everyone responds differently to treatment, but in general:

• CPAP therapy – a sleep apnea treatment that uses gentle, steady air pressure through a mask to keep your airway open while you sleep – has been shown to reduce AHI by an average of 86%.^{15 16}

• Oral appliances, which help keep the airway open by gently moving the tongue or jaw forward, may reduce AHI scores. ^{17 18}

• Sleep position therapy (SPT) has been shown to help reduce AHI in people whose OSA worsens when lying on their backs but may not significantly improve overall sleep quality.¹⁹

Using AHI to measure treatment success

When starting CPAP therapy, your doctor will recommend the best pressure settings. The goal is to find the lowest pressure setting that helps keep airways open and reduces AHI.

Modern CPAP machines collect data so your doctor can monitor treatment effectiveness remotely. If your AHI remains elevated, your doctor may adjust pressure settings for better performance. Some machines automatically adjust pressure based on breathing patterns.

Your doctor may also watch for symptom improvement, such as fewer morning headaches, less frequent snoring, higher energy levels during the day or fewer naps, ²⁷ to determine if the CPAP therapy is working. Successful treatment of OSA often depends on maintaining a regular CPAP routine.

Special considerations for interpreting AHI

Many factors affect how the apnea-hypopnea index (AHI) is interpreted, including age. For example, obstructive sleep apnea (OSA) is considered severe for children at lower AHIs compared to adults.

In general, AHI scores increase with age, although older individuals may not accurately report symptoms. This can result in underdiagnosis of OSA among people over the age of 65.²⁰ Older adults are also at higher risk of heart conditions, which can impact treatment decisions.

Weight management can be a key part of OSA treatment for people with excess weight or obesity. Weight loss can lead to improvements in AHI scores,²¹ but is not a standalone cure for OSA. Treatment often works better when weight management is combined with treatments like CPAP.

If you have questions about your AHI score or what it means for your health, talk to your doctor.