Arterial Blood Gas (ABG) 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.

Why this test is done

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.

How to prepare

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.

Sample type

Blood

Other names for this test

blood gas test, arterial blood gases, ABG, oxygen saturation test