We may earn a commission through products purchased using links on this page. Products or services advertised on this page may be offered by an entity that is affiliated with us. Learn more about our process here.

Obstructive sleep apnea (OSA) is a common sleep disorder, believed to affect at least 2% to 4% of people Trusted Source American Academy of Sleep Medicine (AASM) AASM sets standards and promotes excellence in sleep medicine health care, education, and research. See Full Reference . During sleep, people with OSA experience multiple partial or complete obstructions of the airway, termed hypopneas and apneas. Additional symptoms may include loud snoring, gasping or choking, and daytime sleepiness.

If you have recently received a diagnosis of sleep apnea or taken a sleep study, you may have noticed an AHI reading on your results. AHI is short for apnea-hypopnea index Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. See Full Reference . This is a scale doctors use when diagnosing obstructive sleep apnea (OSA).

What Is the Apnea-Hypopnea Index (AHI)?

The apnea-hypopnea index (AHI) is a diagnostic tool for determining the presence and severity of obstructive sleep apnea (OSA).

People with OSA experience a collapse of their airways during sleep. When this causes their breathing to completely stop or reduce to 10% of normal levels Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. See Full Reference for at least 10 seconds, it is called an apnea. Hypopneas occur when your airways partially collapse, resulting in shallow breathing. If your airflow decreases by more than 30% for at least 10 seconds, it can be considered a hypopnea. Apneic and hypopneic events disrupt sleep and lead to lower blood oxygen levels, contributing to long-term health complications Trusted Source National Heart, Lung, and Blood Institute (NHLBI) The NHLBI is the nation's leader in the prevention and treatment of heart, lung, blood and sleep disorders. See Full Reference .

The AHI sleep apnea scale helps doctors calculate the severity of your symptoms. The AHI is different from the central apnea-central hypopnea index (CAHI) used for central sleep apnea, a form of sleep apnea that develops when the brain fails to tell the respiratory muscles to breathe.

How Is AHI Measured?

The apnea-hypopnea index (AHI) represents the average number of apneas and hypopneas you experience each hour during sleep. To measure it, doctors divide the total number of apneic and hypopneic events Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. See Full Reference by the total number of hours you were asleep. To register as an event, an apnea or hypopnea must last at least 10 seconds or longer.

Doctors typically calculate AHI during a sleep study, or polysomnogram, which monitors your brain waves, blood oxygen levels, heart rate, and breathing while you sleep. Polysomnography generally takes place at a sleep laboratory, but some may be able to perform a simplified version at home.

While the AHI is the primary measurement for diagnosing OSA, your doctor may review other metrics to better understand the severity of your OSA. For example, the oxygen desaturation index Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. See Full Reference (ODI) measures how many times per hour, on average, your blood oxygen levels fall below normal for 10 seconds or longer. Another important metric, especially for children, is the level of carbon dioxide in the blood. A high level of carbon dioxide may arise due to a long period of breathing at less than full capacity, even if the airway is not completely blocked.

 

Understanding the Apnea-Hypopnea Index for Adults and Children

The AHI is measured on a numeric scale. Scores for adults are divided into three categories, which correspond to different levels of OSA severity:

  • Mild: An AHI of at least five events per hour, but fewer than 15.
  • Moderate: An AHI of at least 15 events per hour, but fewer than 30.
  • Severe: An AHI of at least 30 events per hour.

While five is the cutoff for adults, an AHI of one or above is sufficient to diagnose obstructive sleep apnea in children. Children breathe faster than adults in order to support their faster metabolism and smaller lung capacity. This is why even one apneic event can have more of an impact for a child.

Although the categories are not as standardized as they are for adults, most sleep experts consider childhood sleep apnea Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. See Full Reference to fall into three categories:

  • Mild: Children with an AHI of one to five events per hour may be diagnosed with mild sleep apnea.
  • Moderate: Children with an AHI of six to 10 events per hour may be diagnosed with moderate sleep apnea.
  • Severe: Children with an AHI of more than 10 events per hour may be diagnosed with severe sleep apnea.

Adolescents may be diagnosed using either the child or adult AHI scale.

Sleep Apnea AHI Chart

Adult AHIPediatric AHI
Mild OSA≥ 5 to < 15 events per hour≥ 1 to ≤ 5 events per hour
Moderate OSA≥ 15 to < 30 events per hour> 5 to ≤ 10 events per hour
Severe OSA≥ 30 events per hour> 10 events per hour

Drawbacks of the AHI

While the AHI can help doctors diagnose OSA, it does not take into account all factors which may point to the severity, or existence, of OSA.

Hypopneas May Be Measured Differently

Most experts agree on the standard definition of an apnea as a reduction in airflow of at least 90%. Hypopneas are more subjective, since they occur when your airways partially collapse. As a result, there is no standard measurement for what counts as a hypopnea.

Experts have experimented with defining hypopneas according to a certain percentage of decreased airflow, coupled with associated changes in blood oxygen levels or arousals from sleep. However, there is no set definition, and as a result, different definitions of hypopnea can lead to different AHI scores.

The AHI Exclusively Measures the Number of Respiratory Events

The AHI only tells you how often you experience a pause in breathing during sleep. It does not reveal other important elements about that breathing event which could point to the severity of your OSA. For example, it does not show how that pause in breathing affects your blood oxygen levels, which, when repeatedly decreased over time, may increase your risk of related conditions like hypertension and diabetes.

The AHI also does not measure how long an apnea or hypopnea lasts; only that it occurs for at least 10 seconds. People with apneas lasting 30 seconds may experience greater consequences than people whose apneas last 10 seconds.

Since the AHI represents an average taken across the night, it does not reveal patterns in breathing from hour to hour, or connections between sleep position and apneic events. Moreover, since the AHI is calculated during one night in a sleep lab, it might not be accurate for someone whose AHI changes from night to night.

Home Sleep Tests Underestimate the AHI

Home sleep tests calculate the AHI based on the total recording time, as opposed to the more precise total sleep time measured in a polysomnogram. As a result, at-home sleep tests often underestimate AHI by about 15%.

It is important to note these shortcomings of the AHI, because they can affect treatment. If doctors rely solely on AHI when recommending treatment, it may lead them to overlook other aspects of the person’s health history and their related symptoms. For example, for people with a high AHI but no daytime sleepiness, common OSA treatments may be less effective at reducing the risk of hypertension Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. See Full Reference or related cardiovascular conditions. Scientists are still debating how best to incorporate other diagnostic criteria, such as daytime sleepiness, blood oxygen levels, and blood pressure, for a fuller picture of OSA.

The Impact of OSA Treatment on the AHI

Continuous positive airway pressure (CPAP) therapy to keep the airway open is the recommended treatment option for obstructive sleep apnea. Studies have found that sleeping with a CPAP device can decrease the AHI by 73% Trusted Source National Library of Medicine, Biotech Information The National Center for Biotechnology Information advances science and health by providing access to biomedical and genomic information. See Full Reference . When people with severe OSA use their CPAP devices for at least six hours, their AHI returns to normal levels (below five events per hour).

Thanks for the feedback - we're glad you found our work instructive!

Thanks for the feedback - we're glad you found our work instructive!

Submitting your Answer...

References

+9 Sources
  1. American Academy of Sleep Medicine. (2014). The International Classification of Sleep Disorders – Third Edition (ICSD-3). Darien, IL.

    https://aasm.org/
  2. Borsini, E., Noguiera, F., & Nigro, C. (2018). Apnea-hypopnea index in sleep studies and the risk of over-simplification. Sleep Science, 11(1), 45–48.

    https://pubmed.ncbi.nlm.nih.gov/29796201/
  3. Ho, V., Crainiceanu, C. M., Punjabi, N. M., Redline, S., & Gottlieb, D. J. (2015). Calibration model for apnea-hypopnea indices: Impact of alternative criteria for hypopneas. Sleep, 38(12), 1887–1892.

    https://pubmed.ncbi.nlm.nih.gov/26564122/
  4. National Heart, Lung, and Blood Institute. (n.d.). Sleep apnea., Retrieved August 30, 2021, from

    https://www.nhlbi.nih.gov/health-topics/sleep-apnea
  5. Pevernagie, D. A., Gnidovec-Strazisar, B., Grote, L., Heinzer, R., McNicholas, W. T., Penzel, T., Randerath, W., Schiza, S., Verbraecken, J., & Arnardottir, E. S. (2020). On the rise and fall of the apnea-hypopnea index: A historical review and critical appraisal. Journal of Sleep Research, 29(4), e13066.

    https://pubmed.ncbi.nlm.nih.gov/32406974/
  6. Temirbekov, D., Güneş, S., Yazıcı, Z. M., & Sayın, İ. (2018). The ignored parameter in the diagnosis of obstructive sleep apnea syndrome: The oxygen desaturation index. Turkish Archives of Otorhinolaryngology, 56(1), 1–6.

    https://pubmed.ncbi.nlm.nih.gov/29988275/
  7. Yu, J. L., & Afolabi-Brown, O. (2019). Updates on management of pediatric obstructive sleep apnea. Pediatric Investigation, 3(4), 228–235.

    https://pubmed.ncbi.nlm.nih.gov/32851328/
  8. Barbé, F., Durán-Cantolla, J., Sánchez-de-la-Torre, M., Martínez-Alonso, M., Carmona, C., Barceló, A., Chiner, E., Masa, J. F., Gonzalez, M., Marín, J. M., Garcia-Rio, F., Diaz de Atauri, J., Terán, J., Mayos, M., de la Peña, M., Monasterio, C., del Campo, F., Montserrat, J. M., & Spanish Sleep And Breathing Network (2012). Effect of continuous positive airway pressure on the incidence of hypertension and cardiovascular events in nonsleepy patients with obstructive sleep apnea: A randomized controlled trial. JAMA, 307(20), 2161–2168.

    https://pubmed.ncbi.nlm.nih.gov/22618923/
  9. Boyd, S. B., Upender, R., Walters, A. S., Goodpaster, R. L., Stanley, J. J., Wang, L., & Chandrasekhar, R. (2016). Effective Apnea-Hypopnea Index (“Effective AHI”): A new measure of effectiveness for positive airway pressure therapy. Sleep, 39(11), 1961–1972.

    https://pubmed.ncbi.nlm.nih.gov/27568799/

Learn More About Sleep Apnea

Sleep Apnea Treatment

Sleep Apnea Treatment

By Jay Summer | January 20, 2023
Sleep Apnea Symptoms

Sleep Apnea Symptoms

By Rob Newsom | January 20, 2023
What Causes Sleep Apnea?

What Causes Sleep Apnea?

By Jay Summer | January 20, 2023
Man with sleeping apnea and CPAP machine

Diagnosing Obstructive Sleep Apnea

By Alexa Fry | January 20, 2023

Sleep Apnea

By Eric Suni | January 20, 2023

Central Sleep Apnea

By Eric Suni | January 20, 2023

How to Use a CPAP Machine for Better Sleep

By Eric Suni | January 20, 2023

Orthopnea

By Eric Suni | January 20, 2023

Sleep Respiratory Rate

By Austin Meadows | January 20, 2023

ASV Machines

By Danielle Pacheco | January 18, 2023