Your blood oxygen level measures how much oxygen is circulating with your red blood cells.
Oxygen levels may be low if someone feels short of breath, is breathing faster than usual, or feels too sick to do their usual daily activities.
Oxygen enters our body through our nose or mouth when we inhale and passes through our lungs into our bloodstream. Once in our bloodstream, the oxygen then goes to cells all over our body. Once cells use oxygen, they create carbon dioxide. Our bloodstream then carries the carbon dioxide back to our lungs, and we breathe it out (exhale it) through our mouth or nose.
Oxygen is tightly regulated within the body because hypoxemia can lead to many acute adverse effects on individual organ systems. These include the brain, heart, and kidneys. Oxygen saturation measures how much hemoglobin is currently bound to oxygen compared to how much hemoglobin remains unbound. At the molecular level, hemoglobin consists of four globular protein subunits. Each subunit is associated with a heme group. Each molecule of hemoglobin subsequently has four heme-binding sites readily available to bind oxygen. Therefore, during the transport of oxygen in the blood, hemoglobin is capable of carrying up to four oxygen molecules. Oxygen saturation refers to the percentage of oxygen in a person’s blood.
If you have lung or heart conditions, your doctor might want you to routinely check your blood oxygen levels at home.
How to measure your oxygen levels
- Pulse oximetry
- Arterial Blood Gas test
- Long term oxygen therapy (LTOT) assessment
- Hypoxic challenge (fitness-to-fly) test
What are normal oxygen level readings?
You can measure oxygen level using a device called a pulse oximeter. A pulse oximeter is a small clip that often attaches to a finger. An easy-to-use device to help you monitor the oxygen level in your blood. It is non-invasive (no needle) and takes just a few seconds to work. The “SpO2” reading on a pulse oximeter shows the percentage of oxygen in someone’s blood.
A normal level of oxygen is usually 95% or higher. Some people with chronic lung disease or sleep apnea can have normal levels around 90%.
- Oxygen level (SpO2) 90% or less This oxygen level is very concerning and may indicate a severe medical problem. Call or go to your nearest emergency room immediately. You may need an urgent x-ray or heart test.
- Oxygen level (SpO2) 91% to 94% This oxygen level is concerning and may indicate a medical problem. Call your health care provider immediately.
Go to a nearby urgent care facility.
- Oxygen level (SpO2) 95% to 100% This oxygen level is normal. Walk around for two minutes and measure your oxygen level again. If your oxygen level falls below 95%, follow the instructions above.
If your home SpO2 reading is lower than 94%, call your health care provider.
Arterial blood gas test
An arterial blood gas (ABG) test measures oxygen and carbon dioxide levels in our blood. It also measures PH.
An arterial blood gases (ABG) test is a blood test. It uses blood drawn from an artery. This is where the levels of oxygen and carbon dioxide can be measured before they enter body tissues.
When combined with a patient’s clinical features, blood gas analysis can facilitate diagnosis and management.
A healthy blood oxygen level varies between 75 and 100 millimeters of mercury (mm Hg).
What causes low blood oxygen levels?
Certain medical conditions can cause your blood oxygen levels to be too low.
Low blood oxygen may make you feel short of breath, tired, or confused. It can also damage your body.
Different situations can cause low oxygen levels as
- Pus, blood, or water filling the air sacs in the lungs
- Blood clots in the lung
- Scarring or loss of lung tissue
- Sudden exercise, if you have heart or lung disease
- Not breathing, in someone who is profoundly intoxicated, for example
Transitioning from low altitude, where the air has a high concentration of oxygen, to high altitude, where there’s a low oxygen concentration.
Injured your head or neck, which can affect your breathing
- Coronavirus disease (COVID-19).
- Carbon monoxide poisoning.
- Smoke inhalation injury.
- Multiple episodes of nausea and/or vomiting.
- Drug overdose.
- Chronic obstructive pulmonary disease (COPD).
- Cystic fibrosis.
- Heart disease.
- Sleep apnea
Normal oxygen Levels for specific conditions that frequently
require oxygen therapy
- In acute asthma, aim at an oxygen level (saturation) of 94–98%
- In cases of pneumonia who are not at risk of hypercapnic
respiratory failure, aim at an oxygen level (saturation) of 94–98%
- In acute breathlessness due to lung cancer, aim at an
oxygen level (saturation) of 94–98% unless there is coexisting COPD.
- In acute deterioration of pulmonary fibrosis or other
interstitial lung diseases, aim at an oxygen level (saturation) of 94–
98% or the highest possible if these targets cannot be achieved
- In most cases of pneumothorax, aim at an oxygen satur ation of 94–98% if the patient is not at risk of hypercapnic
respiratory failure. In patients with pneumothorax having hospital observation
without drainage, the use of high-concentration oxygen (15 L/
min flow rate via reservoir mask) is recommended unless the
patient is at risk of hypercapnic respiratory failure
- In pleural effusion, aim at an oxygen level (saturation) of 94–
98% (or 88–92% if the patient is at risk of hypercapnic respira tory failure) (grade D).
- In pulmonary embolism, aim at an oxygen level (saturation) of
94–98% (or 88–92% if the patient is at risk of hypercapnic
- In acute heart failure, aim at an oxygen level (saturation) of 94–
98% (or 88–92% if the patient is at risk of hypercapnic respira tory failure) (grade D).
- Continuous positive airway pressure (CPAP) with
entrained oxygen or high-flow humidified nasal oxygen to main tain level (saturation) 94–98% (or 88–92% if at risk of hypercapnia)
should be considered as an adjunctive treatment to improve gas
exchange in patients with cardiogenic pulmonary oedema who
are not responding to standard treatment (or non-invasive
ventilation (NIV) if there is coexistent hypercapnia and
acidosis) (grade B).
- In anaemia, aim at an oxygen level (saturation) of 94–98% or
88–92% if the patient is at risk of hypercapnic respiratory
failure (grade D).
- In sickle cell crisis and acute chest syndrome, aim for an
oxygen level (saturation) of 94–98% or aim at the level (saturation) level that
is usual for the individual patient (grade D).
Good practice point regarding sickle cell crisis
Arterial or arterialised capillary blood gases should be
sampled if there is any doubt about the reliability of oximetry
during a sickle cell crisis.
- In myocardial infarction and acute coronary syndromes,
aim at an oxygen level (saturation) of 94–98% or 88–92% if the
patient is at risk of hypercapnic respiratory failure (grade D).
- High concentrations of oxygen should be avoided in
patients with stroke, unless required to maintain normal oxygen
saturation. Aim at an oxygen level (saturation) of 94–98% or 88–92% if
the patient is at risk of hypercapnic respiratory failure (grade D).
- Covid normal oxygen level COVID-19 is a disease caused by a new virus, first seen in
Wuhan China. Since its discovery it has rapidly spread to many
countries across the globe which has resulted in the WHO
declaring that there is a virus pandemic. The symptoms can be
mild and similar to the flu or they can be severe, resulting in
admission to hospital and sometimes to intensive care.
Can I increase my blood oxygen level?
There are some ways to increase the levels of oxygen in your blood, including:
- Breathing in fresh air:
Opening your windows or going outside or by the sea for a walk can increase the amount of oxygen that your body brings in, which increases your overall blood oxygen level.
- (If you smoke) Quitting smoking:
Only two to three weeks after you quit smoking, your circulation will likely improve significantly. After one to nine months, your shortness of breath decreases. Both aspects contribute to your body’s ability to take in more oxygen.
- Practicing breathing exercises:
Simple breathing exercises can open your airways and increase the amount of oxygen in your blood.
- Oxygen therapy
Oxygen therapy can be extremely beneficial for those who frequently experience low oxygen levels, regardless of the reason. Oxygen therapy is a treatment that provides you with supplemental, or extra, oxygen. Although oxygen therapy may be common in the hospital, it can also be used at home.There are different types of devices that can give you oxygen. Some use tanks of liquid or gas oxygen. Others use an oxygen concentrator, which pulls oxygen out of the air.
There are several devices used to deliver oxygen at home. Your healthcare provider will help you choose the equipment that works best for you. Oxygen is usually delivered through nasal prongs (an oxygen cannula) or a face mask.
Sleeping with an oxygen concentrator can help you maintain your oxygen levels throughout the night, and your physician may prescribe this when consulted.
Ask your doctor/physician.
What is normal and abnormal blood oxygen levels during sleep?
Low sleep apnea oxygen level is a sign that your treatment for sleep apnea is not effective. Patients with breathing problems during sleep (sleep apnea, COPD) often have low oxygen levels in their blood. A normal blood oxygen level should be between 94% to 98%. As a result of not breathing for 30 seconds or more during sleep, your sleep apnea oxygen level would drop to 80% or less. Anything below 90% oxygen level is dangerous to your body and require intervention. Another thing to consider is that the brain can only survive 4 minutes once oxygen is completely cut off.
How does Sleep Apnea Oxygen Level affect the body?
Any value of blood oxygen level below 92% is abnormal however, the number of desaturations and the time spent with abnormal oxygen levels is important. If you only desaturated below 92% once or twice during a 7 hour sleep, and the desaturation level lasted only a couple of seconds, it’s not a reason for worry. Your body will be seriously affected when you’ll have long term low oxygen levels.
The low oxygen levels during sleep can make you feel very tired in the morning and will contribute to more restless sleep. When the oxygen levels start to drop, the carbon dioxide levels build up in your blood. This can lead to morning headaches, fatigue and sleepiness during the day.