Apnea Hypopnea Index (AHI)

What Is AHI?

The apnea-hypopnea index (AHI) is a scale that tells whether you have a sleep disorder called apnea and, if so, how serious it is.

Sleep apnea is when you stop breathing for 10 seconds or more while you’re asleep. A similar disorder, hypopnea, is a partial loss of breath for 10 seconds or longer. You might wake up many times during the night to "catch your breath," but you probably won’t know it.

If your doctor thinks you have sleep apnea, they may have you do a sleep study. You’ll spend the night at a sleep center, where you’ll be hooked up to equipment that checks your heart rate, breathing patterns, brain waves, blood oxygen levels, and other vital signs while you sleep. This test is also called polysomnography. In some cases, your doctor might give you a device to wear at home to measure your breathing and blood oxygen levels.

The sleep tests will tell your doctor how many times each hour you have apnea or hypopnea.

What Do the Numbers in the AHI Mean?

The AHI is the number of times you have apnea or hypopnea during one night, divided by the hours of sleep.

  • Normal sleep: An AHI of fewer than five events, on average, per hour
  • Mild sleep apnea: An AHI of five to 14 events per hour
  • Moderate sleep apnea: An AHI of 15 to 29 events per hour
  • Severe sleep apnea: An AHI of 30 or more events per hour

Children are less likely to have sleep apnea episodes. Most specialists see an AHI above 1 as unusual for them. A child typically needs treatment if their AHI is higher than 5.

Treatment After a Moderate or Severe AHI Score

If you score moderate or severe on the AHI, you might need to use a CPAP (continuous positive airway pressure) machine while you sleep. With a CPAP, you wear a mask over your nose that’s attached to a machine with a hose. It blows air into your nose, and that should help keep you from waking often during the night. It also may record your AHI.

Your doctor might also suggest lifestyle changes that will help keep your airways open, like losing weight, exercising, quitting smoking, and sleeping on your side or stomach instead of your back.

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Related Sleep Apnea Testing

The respiratory disturbance index (RDI) is similar to AHI. In addition to apneas and hypopneas, it counts the number of times those events disturb your sleep, called respiratory effort-related arousals.

A sleep study will also check for low blood oxygen levels, called desaturation. The oxygen desaturation index (ODI) is the number of times your blood oxygen falls for more than 10 seconds, divided by the number of sleep hours.

WebMD Medical Reference Reviewed by Melinda Ratini, DO, MS on March 03, 2020

Sources

SOURCES:

Mayo Clinic: "Sleep Apnea."

National Heart, Lung, and Blood Institute: "What is Sleep Apnea?"

American Sleep Apnea Association: "Getting a Sleep Apnea Diagnosis," "Children's Sleep Apnea," "What does AHI represent?" "Children's Sleep Apnea."

Division of Sleep Medicine, Harvard Medical School: "Apnea: Understanding the Results."

Jonas, D., et al. Screening for Sleep Apnea in Adults: An Evidence Review for the U.S. Preventive Services Task Force, Agency for Healthcare Research and Quality, 2017.

Turkish Archives of Otorhinolaryngology: “The Ignored Parameter in the Diagnosis of Obstructive Sleep Apnea Syndrome: The Oxygen Desaturation Index.”

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