How To Read Sleep Study Results: AHI, Oxygen And Sleep Stages

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To read sleep study results, start with the AHI, then check oxygen, sleep stages and arousals. The apnea-hypopnea index (AHI) counts breathing pauses and shallow breaths per hour of sleep. In adults, an AHI under 5 is considered normal (MedlinePlus). The other lines on the report fill in the picture: how well you slept, how low your oxygen fell and how often you woke briefly. This guide explains each number in plain words, with normal ranges from medical sources. It is for education only. Your sleep clinician must interpret your own report.

Have your AHI? Try the AHI calculator to see how the number is worked out.

What Is In A Sleep Study Report?

A sleep study records brain waves, heart rate, breathing and blood oxygen across the night (NHLBI). A report turns that into sections: sleep time and stages, breathing events, oxygen levels, arousals and limb movements. A technologist collects the data and a doctor reviews it, which may take up to two weeks before a follow-up visit (Sleep Foundation). New to the test? Read what happens during a sleep study first.

What Is A Normal Sleep Study?

Normal values depend on the lab, your age, your sex and whether it was your first night (OHRI normal values). The American Thoracic Society (ATS) primer gives these typical numbers for the sleep part of a report (ATS primer):

Measure Typical Normal
Sleep efficiency (time asleep while in bed) About 80%
Sleep latency (time to fall asleep) Under 30 minutes
REM latency (time to first REM) About 60 to 120 minutes
Stage N1 (light) About 5%
Stage N2 About 50%
Stage N3 (deep) About 20%
REM 20 to 25%

A review article gives similar figures: falling asleep in 10 to 20 minutes on average, stage 2 at 45 to 55 percent and REM at 20 to 25 percent (Pulmonary Chronicles). It lists REM latency as 80 to 120 minutes, so sources differ a little. Learn about the stages in stages of sleep, what is deep sleep and what is REM sleep.

Typical Sleep Stage Shares Four cards from the American Thoracic Society primer. N1 about 5 percent. N2 about 50 percent. N3 about 20 percent. REM 20 to 25 percent. Typical Share of the Night ~5%N1 light sleep ~50%N2 sleep ~20%N3 deep sleep 20-25%REM sleep Source: ATS interpreting sleep studies primer. Values vary by lab and age.

Sleep Study Results Explained: AHI And Severity

The AHI is the number of apneas plus hypopneas divided by the hours of sleep (ATS primer). An apnea is a full stop of airflow for at least 10 seconds. A hypopnea is a drop in airflow of at least 30 percent for at least 10 seconds, together with a drop in blood oxygen of 3 percent or an arousal (ATS primer, AASM criteria review). Some insurers use a 4 percent oxygen drop instead, so labs can score the same night a little differently (ATS primer).

The NHS bands are mild at 5 to 14, moderate at 15 to 30 and severe over 30 (NHS). The ATS primer states mild as 5 to 15, moderate as 15 to 30 and severe over 30, so the edges differ slightly by source (ATS primer). Sleep studies can help show which type of sleep apnea you have and how serious it is (NHLBI). Obstructive sleep apnea, the most common type, happens when the airway collapses or is blocked during sleep (MedlinePlus).

AHI Bands Four bands of events per hour: under 5 is normal in adults, 5 to 14 mild, 15 to 30 moderate, over 30 severe. Edges differ slightly between sources. AHI Events per Hour Under 5Normal (adults) 5 to 14Mild 15 to 30Moderate Over 30Severe Sources: MedlinePlus, NHS, ATS primer.

AHI, RDI And RERAs

Some reports also show a respiratory disturbance index (RDI). It adds respiratory effort-related arousals (RERAs) to the count. A RERA is a breathing effort that ends in an arousal without an oxygen drop, and it needs a brain-wave recording to score (ATS primer). Home tests have no brain-wave sensors, so see home sleep apnea test for why their score can read lower.

Oxygen Nadir Sleep Study: What The Numbers Mean

Oxygen results come from the finger clip. The ATS primer lists the oxygen desaturation index (ODI), the mean oxygen level and the nadir, which is the lowest reading of the night. It also lists hypoxemic burden, the share of sleep spent below 90 percent oxygen (ATS primer). The primer does not give a nadir cut-off, and neither did the other pages I could open. So ask your clinician what your own nadir and time below 90 percent mean for you. Do not rely on a number from a forum.

Arousal Index Normal Range And Limb Movements

An arousal is a brief shift out of deeper sleep that you may not remember. The ATS primer gives the normal arousal index as under about 10 to 25 per hour, depending on age. For the periodic limb movement index (PLMI), which counts leg jerks, it gives under 15 per hour in adults (ATS primer). MedlinePlus notes that the same test also helps find narcolepsy, periodic limb movement disorder and REM sleep behavior disorder (MedlinePlus).

Other Report Lines Four cards. Arousal index under about 10 to 25 per hour depending on age. Limb movement index under 15 per hour in adults. Nadir is the lowest oxygen reading. Hypoxemic burden is the share of sleep below 90 percent oxygen. Other Lines on the Report Under 10-25arousals per hourvaries by age Under 15limb movementsper hour, adults Nadirlowest oxygenreading of the night Burdenshare of sleepunder 90% oxygen Source: ATS interpreting sleep studies primer.

A Simple Order For Reading The Report

Polysomnography report interpretation is easier in steps. Doctors read the whole report together, but you can follow along in this order:

  1. Sleep time and efficiency. Did you sleep enough during the test for the data to be useful?
  2. Breathing events. Check the AHI and how it splits by position and by REM sleep.
  3. Oxygen. Look at the nadir, the mean and the time below 90 percent.
  4. Arousals and limb movements. Compare the arousal and limb movement indexes with the ranges above.
  5. Sleep stages. See how much deep sleep and REM you had.

The OHRI page offers normal values for healthy adults split by sex, age and first versus later night, taken from a published meta-analysis (OHRI normal values). That is a reminder that no single normal number fits everyone. Your clinician compares your results with your own age, health and symptoms.

Why One Night Can Mislead

A sleep study is a snapshot of one night. The ATS primer shows an example where a home test gave an AHI of 8.4, and it says the lower number reflected poor sleep efficiency and less REM sleep (ATS primer). Apnea is often worse in certain positions or in REM sleep. In its sample report, the worst AHI was 53 when lying on the back in REM sleep (ATS primer). That is why the report may break results down by position and stage. The ICSD-3 criteria summarized in one review say obstructive sleep apnea can be diagnosed above 15 events an hour even without symptoms, while at 5 to 15 events an hour symptoms are also needed (AASM criteria review). So your symptoms matter as much as the score. Tell your clinician about snoring, gasping and daytime sleepiness. If your night felt very different from normal, tell your clinician.

Questions To Ask Your Clinician

  • What was my AHI, and which scoring rule did the lab use?
  • How was my oxygen, and what does my lowest reading mean?
  • Did my sleep stages and arousals look typical for my age?
  • Was this night like my usual sleep?
  • What are my treatment options, and what is the next step?

What Happens After The Results?

NHLBI says your doctor will review the results and develop a treatment plan for any diagnosed sleep disorder (NHLBI). For obstructive sleep apnea, the NHS lists lifestyle changes, a CPAP machine, a mandibular advancement device, surgery, mouth and face exercises and hypoglossal nerve stimulation (NHS). Read sleep apnea treatment and how to get used to CPAP. Still deciding on a test? See sleep apnea screening tests.

Quick Takeaways

  • AHI under 5 is normal in adults, and 5 to about 15, 15 to 30 and over 30 are mild, moderate and severe.
  • Sleep stages, oxygen, arousals and limb movements each add to the picture.
  • Normal ranges vary by lab, age, sex and night.
  • Your clinician should explain your own numbers.

Related reading: alternatives to CPAP, what causes sleep apnea, how much deep sleep you need and REM sleep behavior disorder.

FAQs About Sleep Study Results

Can One Number Show Whether I Have Sleep Apnea?

The AHI is the main number used to diagnose obstructive or central sleep apnea, but your doctor also uses your symptoms and the rest of the report (MedlinePlus).

Why Is A Home Test AHI Different From A Lab AHI?

Home tests usually count events per recording time and cannot score arousals. The ATS primer’s example shows a lower home AHI linked to poor sleep efficiency and less REM sleep (ATS primer).

Can Two Labs Score The Same Study Differently?

Yes. Scoring rules differ. One accepts a 3 percent oxygen drop for a hypopnea, and another uses 4 percent (ATS primer).

Does A Normal AHI Mean My Sleep Is Fine?

Not always. The AHI only tracks breathing events. The test also looks for narcolepsy, periodic limb movement disorder and REM sleep behavior disorder (MedlinePlus).

How Long Until I Get My Results?

It may take up to two weeks, followed by a review appointment (Sleep Foundation).

Sources