Sleep Apnea Diagnosis and Oxygen Desaturation Effects

One of the most common sleep disorders in people with sleeping difficulties is obstructive sleep apnea (OSA). OSA is diagnosed with a test called an overnight sleep study that records the activity of the body during sleep.

A sleep study can provide doctors with important information about a person's sleep cycle, including how often and how long their breathing pauses (called apnea).

One of the most important measurements is a person's oxygen level during the different stages of sleep. When the level falls below what the body needs to function normally, it is called oxygen desaturation. This not only tells the doctor how severe OSA is but is also an indication of future health concerns.

Oximeter sensor on a patient's finger
Photomick / Getty Images

This article describes what causes oxygen desaturation in people with OSA as well as the symptoms and consequences of untreated OSA. Diagnosis and treatment options are also explored.

What Is Obstructive Sleep Apnea?

Obstructive sleep apnea occurs when your throat muscles relax and block your airway during sleep. When this happens, breathing can stop for anywhere from 10 seconds to over a minute in some cases.

People with OSA experience frequent, repeated pauses in breathing during sleep. Some experience hundreds of these in a night. And, while the person may be completely unaware of these gaps, their partner will often notice and become alarmed.

During these breathing gaps, people receive less air, which causes their blood oxygen levels to drop. While these levels will generally return to normal once regular breathing starts again, frequent breathing gaps can pose serious health concerns. This is why OSA is something you can't ignore.


Obstructive sleep apnea occurs when your throat muscles relax and block your airway repeatedly during sleep, causing your oxygen levels to drop.

Recognizing OSA

Obstructive sleep apnea is often recognized by a person's sleep partner, but what happens if you sleep alone? One of the telltale signs is feeling sleepy the next day even if you have had a full night's rest.

Depending on the severity of the condition, other symptoms may occur, including:

  • Loud snoring, snorting, gasping, or choking during sleep
  • Night sweats
  • Nocturia (nighttime urination)
  • Nighttime acid reflux
  • Dry mouth when awakening
  • Insomnia
  • Headaches
  • Irritability
  • Memory problems
  • Depression
  • Low sex drive
  • Weight gain

Risk Factors

You should also suspect OSA if you have risk factors for the disorder. People of any age, sex, or weight can have OSA, but it is much more common in people who:

  • Are assigned male at birth
  • Are over 50 years of age
  • Are obese
  • Smoke cigarettes
  • Sleep on their back
  • Regularly use alcohol or sedatives (medications for sleep and anxiety)
  • Have enlarged tonsils or adenoids
  • Have hypothyroidism (underactive thyroid gland)
  • Have had a stroke
  • Have certain head and face features contributing to narrow upper airway"
  • Have a neck circumference of 17 inches or more for someone assigned male at birth or 16 inches or more for someone assigned female at birth


Obstructive sleep apnea not only causes symptoms that awaken you or your partner during the night (like loud snoring, choking, or night sweats) but also daytime sleepiness, headaches, irritability, and memory problems.


If a doctor suspects you may have obstructive sleep apnea, they may refer you to a specialist called a somnologist, or sleep doctor. After a review of your symptoms, you may be given an in-office exam that estimates your risk of OSA based on:

  • Snoring
  • Tiredness
  • Observed apnea
  • Blood pressure
  • Body Mass Index (BMI)
  • Age
  • Neck circumference
  • Sex assigned at birth

Based on the findings, the doctor may recommend an overnight sleep study, also known as level 1 polysomnography or a home sleep test. Considered the gold standard for the diagnosis of OSA, the test involves connecting you to sensors that monitor your temperature, heart rate, brain waves, breathing rate and depth, nasal and mouth airflow, and body movements during sleep.

One of the more important tools in a sleep study is a pulse oximeter. This is a device that is clamped to your finger to monitor your blood oxygen levels.

Role of Pulse Oximetry

If you are getting enough oxygen during the day, your blood oxygen level will generally be between 95% and 100%. This is called oxygen saturation. During sleep. your breathing rate slows, so 90% is considered normal.

With obstructive sleep apnea, repeated gaps in breathing cause blood oxygen levels to drop by 3% or more, leading to oxygen desaturation. Oxygen levels are considered abnormal when they drop below 90%. They might be considered to be severely abnormal when they are below 80%.

The severity of OSA is measured based not only on blood oxygen levels but also how frequently and how long breathing stops, and how much airflow is reduced. Breathing gaps of longer than 10 seconds with airflow reductions of 30% or more are considered problematic.

If there are five to 15 of these events per hour, it is considered mild OSA; 15 to 29 of these events per hour is classified as moderate OSA. If 30 or more, the condition is classified as severe OSA.

If left untreated, OSA can do more than cause daytime sleepiness and irritability. Over time, it can increase the risk of high blood pressure, coronary artery disease (CAD), atrial fibrillation, and type 2 diabetes. This is why the treating OSA is so important, especially when it is moderate to severe.


Obstructive sleep apnea is best diagnosed with an overnight sleep study. The diagnosis is based on multiple factors, including your blood oxygen levels, airflow levels, and the frequency and duration of breathing gaps during sleep.


The treatment of obstructive sleep apnea varies depending on how severe the condition is. Treatment options may include:

  • Devices to help change your sleep position
  • Nasal steroids if allergies are affecting breathing
  • Continuous positive air pressure (CPAP) therapy, a device you wear at night that delivers pressurized room air through a mask
  • Tonsillectomy or adenoidectomy, surgery to remove the tonsils and/or adenoids, for children with OSA
  • Uvulopalatopharyngoplasty, surgical removal of the fleshy part of the soft palate
  • Weight loss


Obstructive sleep apnea (OSA) is a sleep disorder caused when throat muscles relax and interfere with breathing. Frequent and prolonged gaps can reduce the level of oxygen in the bloodstream.

Untreated OSA can lead to serious health problems, including an increased risk of high blood pressure, heart disease, and diabetes. This is why it is important to get diagnosed if you have symptoms and risk factors of OSA.

OSA is typically diagnosed with an overnight sleep study that, among other things, measures your blood oxygen with a pulse oximeter. Depending on the results of these and other tests, a doctor can decide which treatment options are best for you.

Frequently Asked Questions

  • What is a normal blood oxygen level during sleep?

    Oxygen levels above 90% are considered normal when sleeping. It's normal for your oxygen level to be slightly lower when you're asleep than when you're awake.

  • How do you monitor oxygen levels when sleeping?

    Overnight pulse oximetry monitors your blood oxygen levels while you are sleeping. You'll wear a finger clip that uses infrared sensors to measure oxygen in your hemoglobin (the protein in your blood that carries oxygen).

5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Brandon Peters, MD
Brandon Peters, MD, is a board-certified neurologist and sleep medicine specialist.