COPD
Measuring Oxygen Saturation and Testing for Hypoxemia
ByDeborah Leader, RN
Updated on June 03, 2024
Medically reviewed bySusan Russell, MD
Oxygen saturation, or "O2 sat" for short, is a measure of how much oxygen is in your blood. For most healthy adults and children, a normal oxygen saturation level is between 95% and 100%. Hypoxemia occurs with lower levels of oxygen in the blood and can lead to complications or even death at dangerously low levels below 90%.
An oxygen saturation below 90% requires medical attention because it means your body isn't getting enough oxygen to function properly. It is monitored through pulse oximetry (a device typically clipped to the finger) or through arterial blood gas testing.
This article covers conditions that affect the amount of oxygen in your blood and the complications of having low oxygen saturation. You will also learn how to measure your blood oxygen levels at home (if recommended) and when to seek treatment.
Conditions That Cause Low Oxygen Levels
Blood disorders, problems with circulation, and lung issues can prevent your body from absorbing or transporting enough oxygen. When this happens, it can lower your blood's oxygen saturation level.
Examples of conditions that can affect your oxygen saturation include:
- Respiratory infections (e.g., a cold, the flu, COVID-19): Any condition that affects your ability to breathe will affect your oxygen intake
- Chronic obstructive pulmonary disease (COPD): A group of chronic lung diseases that make it difficult to breathe
- Asthma: A chronic lung disease that causes airways to narrow
- Pneumothorax: A partial or total collapse of the lung
- Anemia: Not having enough healthy red blood cells
- Heart disease: A group of conditions that affect the heart's function
- Pulmonary embolism: When a blood clot causes blockage in an artery of the lung
Congenital heart defects are structural heart conditions present at birth. They also can contribute to low oxygen levels in the blood.
Other Causes of Low Oxygen Levels
A drop in oxygen saturation in the blood is called hypoxemia.
It can be caused by situational factors, like:
- Less oxygen in the air (for example, when you are flying in an airplane)
- Breathing in carbon monoxide, cyanide, or another substance that binds more strongly to hemoglobin than oxygen does
- Medications, such as narcotics, that can cause breathing to slow
Conditions that affect breathing, oxygen absorption, and red blood cell or hemoglobin count can also cause low O2 sat.
Are Home Pulse Oximeters Useful for COVID Recovery?
How to Measure Oxygen Levels
Oxygen saturation is measured in one of two ways: an arterial blood gas test (ABG or Sa02) or pulse oximetry (Sp02).
ABG is usually only done in a hospital, while pulse oximetry can be done in other healthcare settings (like a provider's office) and even at home.
The 4 Best Pulse Oximeters to Use at Home, Tested and Reviewed
ABG
An ABG value refers to the levels of oxygen and carbon dioxide in blood running through your veins.
During an ABG, a healthcare provider draws blood from an artery, such as the radial artery in the wrist or the femoral artery in the groin. The sample is immediately analyzed by a machine or in a lab.
Your ABG value can give your healthcare provider a sense of how efficiently your hemoglobin—the protein in red blood cells that transports oxygen throughout the body—exchanges oxygen and carbon dioxide.
What Do Arterial Blood Gases (ABGs) Measure?
Pulse Oximetry
A pulse oximetry reading reflects the percentage of oxygen saturation in arterial blood. It will generally read at about two percentage points higher or lower than the ABG results.
Unlike the ABG test, pulse oximetry does not involve a needle. Instead, the test uses a sensor to read wavelengths reflected from the blood. The probe is attached to your finger, earlobe, or another place on the body. Some studies have shown that the right middle finger works best. In some people, the right thumb may also work well.
A pulse oximeter can give results on a screen in just a few seconds. Most oximeters work best when used on the middle finger. Nail polish can interfere with oximeter measurement. If at-home monitoring is recommended, you can check your oxygen saturation levels using wearable pulse oximetry devices.
Even some smartwatches even have this feature. You can also buy a pulse oximetry device at your local pharmacy or online.
| Oxygen Saturation Levels | ||
|---|---|---|
| Reading | ABG Level | O Sat Result |
| Below Normal | < 80 mmHg | < 95% |
| Normal | > 80 mmHg | 95% to 100% |
What Is a Dangerously Low Oxygen Level?
Most people need an oxygen level of 89% or more to ensure that cells in your body have the oxygen they need to work. Low oxygen saturation in the blood can mean there's less oxygen in the body's tissues, including the organs and muscles. When this happens, it's called hypoxia.
If the level falls for a short time, permanent damage isn't likely. Your cells can adapt to a lack of oxygen when the deficiency is small. But repeated episodes (caused by a lung condition or sleep apnea, for example) can cause damage. Oxygen levels above 90% are normal when you're asleep, so you should see a healthcare provider to diagnose any lower levels.
A level that falls to 88% or less requires immediate care.
Keep in mind that a pulse oximeter may not work at an extremely low level of 80% or less oxygen saturation. Other factors that can affect accuracy include skin thickness or pigment, cold hand temperature, and whether or not you smoke.
Sleep Apnea and Low Blood Oxygen During Sleep
Hypoxia usually happens because there is not enough oxygen in the blood (hypoxemia). However, it can also happen when:
- There are not enough red blood cells to carry oxygen to the tissues due to severe bleeding, after a trauma, or conditions like sickle cell anemia.
- There is inadequate blood flow due to a stroke, in which there is low blood flow to a region of the brain, or a slow heart rhythm or heart attack, in which there is low blood flow to the heart muscles.
- The tissues require even more oxygenated blood than can be delivered due to severe infections that cause sepsis, which may result in hypoxemia and eventually organ failure.
With larger deficiencies, cell damage and cell death can happen and, in some cases, prove fatal.
| Pulse Ox Reading | Heart Rate | What You Should Do |
| 95% to 100% | 60-100 | Normal |
| 95% | 101-109 | Continue monitoring |
| 93% to 94% | 110-130 | Call your healthcare provider |
| 92% or lower | 131 or higher | Call 911 or go to the ER |
What Does An Oxygen Desaturation Index (ODI) Mean?
Treating Low Oxygen Saturation
Generally speaking, an oxygen saturation level below 95% is considered abnormal. This should be evaluated by a healthcare provider. An oxygen saturation level below 90% requires emergency medical attention.
Raising Blood Oxygen Levels Quickly
The following can help raise blood oxygen quickly:
- Sit up straight rather than lying flat. Keep in mind that if your oxygen levels have fallen due to low blood flow (as with a stroke or heart rhythm change), this position may not help.
- Get some fresh air or go inside if you are outdoors and it is very hot/very cold.
- Cough to loosen up any mucus (like from allergies or a cold/the flu).
- Take deep, full breaths to get oxygen into your blood.
If oxygen saturation is dangerously low, they will need oxygen therapy—sometimes urgently. A healthcare provider will also need to quickly diagnose and treat the underlying problem, often by using tests that include a chest X-ray or an electrocardiogram (heart rhythm reading).
An oxygen level of 85% or less requires immediate care for critical illness. The brain is the most susceptible organ to hypoxia. Brain cells can begin to die within five minutes of oxygen deprivation. If hypoxia lasts longer, it can lead to coma, seizures, and brain death. It is very important to find out the cause of low oxygen saturation so the problem can be fixed.
The full treatment plan will depend on the cause of the low saturation levels.
COPD and Asthma
With chronic conditions like COPD and asthma, the cause of hypoxia is usually low air exchange in the lungs and alveoli. In addition to oxygen therapy, steroids or rescue inhalers (bronchodilators) might be needed to open the airways.
Cardiovascular Conditions
In circulatory conditions like heart disease, impaired blood flow reduces oxygen delivery. In this case, medications that improve heart function, such as beta-blockers for heart failure or prescription medications to treat heart arrhythmias, can help improve oxygen saturation.
Anemia
With anemia, the blood supply to the tissues is reduced because there are not enough healthy red blood cells with hemoglobin to carry oxygen. Sometimes, a red blood cell transfusion is necessary to increase a person's level of healthy red blood cells.
Oxygen Saturation and COPD
Summary
Oxygen saturation is the measure of how much oxygen is traveling through your body in your red blood cells. Normal oxygen saturation for healthy adults is usually between 95% and 100%.
If you have a chronic health condition that affects your lungs, blood, or circulation, regularly tracking your oxygen saturation may be recommended. An oxygen saturation level below 95% is not normal. A level under 90% requires emergency care.
14 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 Deborah Leader, RN
Deborah Leader RN, PHN, is a registered nurse and medicalwriter who focuses on COPD.
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