Health Topics
What is an arterial blood gas test?
An arterial blood gas (ABG) test measures the amount of oxygen and carbon dioxide (CO2) in a sample of your blood. The blood oxygen measurement shows how well your lungs move oxygen from the air into your blood when you breathe in. The carbon dioxide measurement shows how well your lungs remove carbon dioxide from your blood when you breathe out.
Most blood tests take a sample from a vein. For this test, a health care provider will take a sample of blood from an artery (a blood vessel that carries oxygen-rich blood from your heart and lungs to your body). That's because blood from an artery has higher oxygen levels than blood from a vein.
An ABG test usually includes the following levels:
- Oxygen saturation (O2 Sat). This measures how much oxygen your red blood cells are carrying.
- Partial pressure of oxygen (PaO2). This measures the pressure of oxygen that's dissolved in your blood. It helps show how well your lungs move oxygen from the air into your blood when you breathe in.
- Partial pressure of carbon dioxide (PaCO2). This measures the amount of carbon dioxide (an acidic waste product that your body makes naturally) in your blood. It also shows how well your lungs remove carbon dioxide from your blood when you breathe out.
- Acid-base balance (pH level). This measures the acidity of your blood. Too much acid is called acidosis. Too much base (alkaline) is called alkalosis. If your blood and tissues become even slightly too acidic or too basic (alkaline), it can affect many of your organs and even become life-threatening.
An ABG test may also measure your bicarbonate (HCO3) concentration. Bicarbonate is an electrolyte. Electrolytes are electrically charged minerals that help control the amount of fluids and the balance of acids and bases (pH balance) in your body. Most of the carbon dioxide in your blood is stored as bicarbonate. So, this measurement can help show your carbon dioxide levels.
Other names: blood gas test, arterial blood gases, ABG, oxygen saturation test
What is it used for?
An ABG test is used to help:
- Diagnose serious problems with your lungs and breathing. Your lungs are responsible for getting oxygen into your blood, CO2 out of it, and for helping to keep your pH balance normal.
- Diagnose kidney disorders. Like the lungs, your kidneys help to keep your pH balance normal. They also help your body remove CO2.
- Find out whether treatment is working for breathing disorders, kidney disease, or other conditions that may affect your acid-base balance.
Why do I need an arterial blood gas (ABG) test?
There are many reasons why you may need this test. For example, you may need an ABG test if you:
- Have symptoms of acidosis (too much acid in your blood), such as:
- Uncontrolled rapid or deep breathing, which may be a sign that your lungs are trying to adjust acids or bases by changing the amount of oxygen or carbon dioxide in your blood.
- Arrhythmia. (a problem with the rate or rhythm of your heartbeat).
- Confusion.
- Fatigue.
- Have symptoms of alkalosis (too little acid in your blood), such as:
- Confusion.
- Nausea and vomiting.
- Muscle twitching and/or cramps.
- Numbness in hands, feet, or face.
- Arrhythmia.
- Are being treated for a lung disease or a condition that affects your breathing, such as:
- Asthma.
- Chronic obstructive pulmonary disease (COPD).
- Cystic fibrosis.
- Myasthenia gravis.
- Have symptoms of:
- Carbon monoxide poisoning.
- An inhalation injury (breathing in smoke, hot air, and/or harmful chemicals).
- A recent head or neck injury that could affect your breathing.
- Are receiving oxygen therapy in the hospital.
What happens during an arterial blood gas test?
The sample is usually taken from an artery on the inside of your wrist, but it may be taken from an artery in your arm or groin. For a newborn, the sample may be taken from the baby's heel or the umbilical cord shortly after birth.
If your blood sample is taken from your wrist, the provider will first test your blood circulation by applying pressure to the arteries in your wrist in order to cut off blood flow to your hand for several seconds. Then the provider will let go of your wrist to check how quickly blood flow returns to your hand. If your blood flow is normal, the provider will collect a blood sample.
A blood sample taken from an artery tends to be more uncomfortable than most blood tests, which use a vein. So, the provider may apply some numbing medicine to your skin after testing your circulation. The provider will insert a needle with a syringe into the artery to remove some blood.
When the syringe is full, the provider will bandage the puncture site. Pressure will be applied to the site for at least 5 minutes to stop the bleeding.
Will I need to do anything to prepare for the test?
You may need to stop taking certain medicines before this test, so tell your provider about all the medicines and supplements you take. But don't stop taking any medicines unless your provider tells you to.
- If you take blood thinners, including aspirin, ask your provider whether you should stop taking them before your test.
- Certain medicines may also upset your acid-base balance and lead to abnormal ABG test results.
If you are on oxygen therapy, your oxygen may be turned off for about 20 minutes before the test. This will be done only if you can breathe without oxygen therapy.
Are there any risks to the test?
There is very little risk to having an arterial blood gas test. You may have some bleeding, bruising, or soreness at the spot where the needle was put in. Very rarely, the needle may damage a nerve or the artery. You may be told to avoid lifting heavy objects for 24 hours after the test.
What do the results mean?
ABG test results involve many body systems that affect each other. There are also many health conditions that can cause abnormal results. For these reasons, it's best to have your provider explain what your results mean for your health.
Generally, for each of the following measurements, your ABG test results will also list their normal ranges:
- Oxygen saturation (O2Sat). 95-100%.
- Partial pressure of oxygen (PaO2). 75-100 millimeters of mercury (mmHg).
- Partial pressure of carbon dioxide (PaCO2). 35-45 mmHg.
- Acid-base balance (pH level). 7.35-7.45.
- Bicarbonate (HCO3). 22-26 milliequivalents per liter (mEq/L).
An ABG test alone usually can't provide a diagnosis. So, if your results are not normal, your provider will likely order more tests. In general, abnormal results may mean you have a problem with your lungs or kidneys or a metabolic disorder. Metabolic disorders affect how your body uses food for energy.
Learn more about laboratory tests, reference ranges, and understanding results.
Is there anything else I need to know about an arterial blood gas test?
Another type of test, called pulse oximetry, can check your blood oxygen saturation levels. A small clip-like device, called a pulse oximeter, is usually attached to your finger. The device tells you the percentage of red blood cells that are full of oxygen. Pulse oximetry may be useful if blood oxygen levels are the only concern. Ask your provider if this test is right for you.
References
- American Lung Association [Internet]. Chicago: American Lung Association; c2025. How Lungs Work; [updated 2025 Apr 22; cited 2025 June 9]; [about 3 screens]. Available from: http://www.lung.org/lung-health-and-diseases/how-lungs-work
- Merck Manual Consumer Version [Internet]. Kenilworth (NJ): Merck & Co. Inc.; c2025. Acid-Base Disorders; [revised 2025 Mar; cited 2025 Jun 9]; [about 4 screens]. Available from: https://www.merckmanuals.com/home/hormonal-and-metabolic-disorders/acid-base-balance/overview-of-acid-base-balance
- Merck Manual Consumer Version [Internet]. Kenilworth (NJ): Merck & Co. Inc.; c2025. Arterial Blood Gas (ABG) Analysis and Pulse Oximetry; [revised 2023 Nov; cited 2025 Jun 9]; [about 2 screens]. Available from: https://www.merckmanuals.com/home/lung-and-airway-disorders/diagnosis-of-lung-disorders/arterial-blood-gas-abg-analysis-and-pulse-oximetry
- National Cancer Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; NCI Dictionary of Cancer Terms: Oxygen saturation test; [cited 2025 Jun 9]; [about 1 screen]. Available from: https://www.cancer.gov/publications/dictionaries/cancer-terms/def/oxygen-saturation-test
- National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; How the Lungs Work; [updated 2022 Mar 24; cited 2025 Jun 9]; [about 2 screens]. Available from: https://www.nhlbi.nih.gov/health/lungs
- Nurse.org [Internet]. Bellevue (WA): Nurse.org; Arterial Blood Gases (ABGs) Explained; [updated 2025 May 13; cited 2025 Jun 9]; [about 12 screens]. Available from: https://nurse.org/articles/arterial-blood-gas-test
- Testing.com [Internet]. Seattle (WA): OneCare Media; c2025. Blood Gases; [modified 2021 Dec 13; cited 2025 Jun 9]; [about 24 screens]. Available from: https://www.testing.com/tests/blood-gases/
The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.