What is an arterial blood gas test?

An arterial blood gas (ABG) A test assesses the oxygen, CO2 levels and blood acidity, known as the pH level or acid-base balance, in your blood. It obtains a sample from an artery, which transports oxygenated blood from the lungs to the body. In an ABG test, The blood oxygen measurement shows the efficiency of the lungs in transferring oxygen from air to blood during inhalation. The carbon dioxide measurement indicates the effectiveness of the lungs in removing carbon dioxide from blood during exhalation.

Carbon dioxide, produced by your body, is a waste product that is acidic in nature. A slight change in the acidity level of your blood and tissues, either being too acidic or too alkaline, can have severe consequences on your organs and even be 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.

A blood sample taken from the wrist is preceded by a blood circulation test. The provider will temporarily stop blood flow to the hand by applying pressure to the wrist arteries, then release the pressure to assess blood return speed. Upon normal blood flow, the sample is collected.

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). It measures the oxygen-carrying capacity of red blood cells.
  • Partial pressure of oxygen (PaO2). This tests the pressure of dissolved oxygen in the blood, indicating the effectiveness of oxygen transfer from the lungs to the bloodstream.
  • Partial pressure of carbon dioxide (PaCO2). It measures the concentration of carbon dioxide in the 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 a single test is rarely conclusive in diagnosing. If the results are abnormal, further tests will likely be ordered to make a diagnosis. Abnormal results may indicate issues with the lungs, 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.

 

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.