Arterial Blood Gas (ABG) Test

What is an arterial blood gas test?

An arterial blood gas (ABG) test measures the amount of oxygen and carbon dioxide in your blood. It also checks the acidity of your blood. This is called your acid-base balance or your pH level. The blood sample is taken from an artery, which is a blood vessel that carries oxygen-rich blood from your lungs to your body.

In an ABG test, the blood oxygen measurement shows how well your lungs move oxygen from the air into your blood when you breath in. The carbon dioxide measurement shows and how well your lungs remove carbon dioxide from your blood when you breath out.

Carbon dioxide is an acidic waste product that your body makes. If your blood and tissues become even slightly too acidic or too basic (alkaline), it can seriously affect many of your organs and even become life-threatening.

Your lungs and your kidneys do much of the work to keep your acid-base balance normal. So, the acid-base measurement from an ABG test can help diagnose and monitor conditions that affect your lungs and kidneys as well as many other conditions that may upset your acid-base balance.

Other names: blood gas test, arterial blood gases, ABG, oxygen saturation test

What is it used for?

An ABG test is used to help:

• Check your acid-base balance
• Diagnose serious problems with your lungs and breathing
• Diagnose kidney disorders
• 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 a problem with your acid-base balance, 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
  • Nausea and vomiting
  • Arrhythmia (a problem with the rate or rhythm of your heartbeat)
  • Confusion
  • Fatigue
  • Muscle twitching and/or cramps
• 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 after you have had:
  • 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 a blood oxygen level test?

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. That's because blood from an artery has higher oxygen levels than blood from a vein.

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. The provider will hold your wrist and apply pressure to the arteries 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 first. 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?

If you take blood thinners, including aspirin, ask your health care provider whether you should stop taking them before your test. And tell your provider about all other medicines and supplements you take. But don't stop taking any medicines unless your provider tells you to.

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 a blood oxygen level 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. And there are 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.

Your ABG test results will list many measurements, including:

• Oxygen saturation (O2Sat). 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 oxygen moves from your lungs to your bloodstream.
• Partial pressure of carbon dioxide (PaCO2). This measures the amount of carbon dioxide in your blood. It also shows how easily carbon dioxide can move out of your body.
• 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. These conditions are symptoms of other problems that upset the acid-base balance in your body.

An ABG test alone usually can't provide a final diagnosis. So, if your results are not normal, your provider will likely order more tests to make a diagnosis. 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. Certain medicines may also upset your acid-base balance and lead to abnormal ABG test results.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about blood oxygen level tests?

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.