How do I read my sleep study results?

The main number on a sleep study report is the apnea-hypopnea index (AHI) for a lab study, or the respiratory event index (REI) for a home test.¹ Both count pauses in breathing and shallow breaths per hour.^{2, 3} For adults, under 5 per hour is normal, and higher numbers fall into the mild, moderate or severe range for sleep apnea.¹

By Wesper. Published November 2, 2026.

What is the main number on a sleep study report?

The main number is a breathing index. It shows how many times per hour your breathing stopped or became shallow. A pause in breathing that lasts at least 10 seconds is called an apnea. A period of reduced, shallow breathing is called a hypopnea.⁴

Your study was ordered by a medical provider and done either overnight in a sleep lab or at home. A study in a sleep lab usually reports the AHI, or apnea-hypopnea index. The AHI is the number of apneas plus hypopneas, divided by the hours you were asleep.²

Home sleep apnea tests generally use the REI, or respiratory event index.^{1, 2} Home tests usually do not record brain waves, so they do not measure sleep stages directly.^{2, 3} Instead, the REI divides the breathing events by monitoring time, which is the recording time with periods of poor signal and estimated awake time taken out.² You can read more in our guide to the REI and how it differs from the AHI.

What do the severity ranges mean?

The severity ranges show whether your AHI or REI is in the normal range or in the mild, moderate or severe range for obstructive sleep apnea (OSA). The American Academy of Sleep Medicine (AASM) uses the same ranges for both numbers in adults.¹

These ranges help your doctor describe your results. Only a medical provider can diagnose sleep apnea.⁵ The AASM also says testing should be part of a full sleep evaluation with follow-up care.³

What do the oxygen numbers mean?

The oxygen numbers show what happened to the oxygen level in your blood during the night. Both in-lab studies and home tests measure blood oxygen.^{6, 7}

One oxygen number you may see is the ODI, or oxygen desaturation index. It is the average number of times per hour of the study that your blood oxygen dropped by a set amount.⁸ Depending on the rules your sleep center uses, a drop counts if oxygen falls by at least 3% or at least 4%.⁸

The ODI is a separate number from your AHI or REI. Your breathing index counts pauses and shallow breaths, and the ODI counts oxygen drops.^{2, 8} Our article on the oxygen desaturation index goes into more detail.

What else might be on your report?

Depending on the type of test, your report may also show sleep stages, leg movements or heart rate.^{6, 7} An in-lab sleep study, also called a polysomnogram, records your brain waves, heartbeats and breathing. It also tracks your eye, leg and arm movements and the oxygen level in your blood.⁶

A sleep technologist scores an in-lab study by marking your sleep stages and any events of abnormal breathing or leg movement.⁶ That is why a lab report may list your sleep stages and leg movements. Some lab reports also list an RDI, or respiratory disturbance index, which adds a third type of breathing event called a respiratory effort-related arousal.²

A home sleep apnea test report focuses on breathing. These devices measure your breathing and blood oxygen level, and some also measure heart rate or other information about your body.⁷ For more of the terms you may see, read our explanation of sleep and respiratory metrics.

Why might two reports show different numbers?

Two reports can show different numbers because sleep centers may use different rules to count shallow breaths. The AASM's recommended rule counts a hypopnea when reduced airflow comes with a 3% drop in oxygen or a brief arousal seen in the brain waves. An alternative rule counts it only when there is a 4% drop in oxygen.³

Depending on which rule is used, the AHI can be quite different for the same person.³ Home tests that use standard sensors cannot detect shallow breaths that are linked only to a brief arousal in the brain.³ Breathing can also change from night to night, which is another reason two tests may not match.³

The hours used in the math matter as well, because the AHI divides by sleep time and the REI divides by monitoring time.² Illustrative example: 60 breathing events over 6 hours of sleep works out to 10 per hour, and the same 60 events over 8 hours of monitoring works out to 7.5 per hour. Our article on the 3% and 4% hypopnea rules explains the scoring rules in more detail.

What happens next?

Next, a doctor reviews your results and uses them to make a diagnosis and plan treatment if you need it.⁶ For a home test, the raw data must be reviewed by a physician who is board-certified in sleep medicine or overseen by one.⁵ A diagnosis must not be based on computer scoring alone.⁵ Scoring and review of a home test may take several days or weeks.⁷

A negative home test cannot rule out sleep apnea. If your symptoms still fit, further testing is needed.⁷ The AASM recommends an in-lab sleep study when a home test is negative, unclear or did not record enough usable data.³ Our article on what happens after a negative home sleep test walks through this step.

Frequently asked questions

What is a normal AHI?

For adults, an AHI or REI under 5 events per hour is considered normal.¹ Your doctor will look at your result together with your symptoms.

What is the difference between AHI and REI?

AHI counts apneas and hypopneas per hour of sleep and is used for in-lab studies. REI counts breathing events per hour of monitoring time and is used for home sleep apnea tests.²

What does ODI mean on a sleep study?

ODI stands for oxygen desaturation index. It is the average number of times per hour that your blood oxygen dropped by a set amount during the study.⁸

Can I have sleep apnea symptoms with a normal result?

Yes. A negative home sleep apnea test cannot rule out sleep apnea, so further testing is needed if your symptoms still fit.⁷ If an in-lab study is negative and your doctor still suspects sleep apnea, a second in-lab study may be considered.³

Talk with your doctor or sleep provider about your results, especially if a number or term on your report is unclear or your symptoms continue. Bring your report to the visit so you can go through it together.

This article is for general education and is not medical advice. Talk with a licensed medical provider about your symptoms and testing options.

Sources

1. American Academy of Sleep Medicine. Quality Measure #277: Sleep apnea severity assessment at initial diagnosis. Version 9.0, December 2024. aasm.org
2. American Academy of Sleep Medicine. AASM style guide for sleep medicine terminology. Updated November 2015. aasm.org
3. Kapur VK, Auckley DH, Chowdhuri S, Kuhlmann DC, Mehra R, Ramar K, Harrod CG. Clinical practice guideline for diagnostic testing for adult obstructive sleep apnea: an American Academy of Sleep Medicine clinical practice guideline. J Clin Sleep Med. 2017;13(3):479-504. aasm.org
4. Centers for Medicare & Medicaid Services. National Coverage Determination 240.4: CPAP therapy for obstructive sleep apnea. cms.gov
5. Rosen IM, Kirsch DB, Carden KA, et al. Clinical use of a home sleep apnea test: an updated American Academy of Sleep Medicine position statement. J Clin Sleep Med. 2018;14(12):2075-2077. aasm.org
6. American Academy of Sleep Medicine. Sleep study. Sleep Education patient page, reviewed September 2020. sleepeducation.org
7. American Academy of Sleep Medicine. Home sleep apnea test. Sleep Education patient page, reviewed August 2020. sleepeducation.org
8. LOINC. 90567-9: Oxygen desaturation index. loinc.org