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Arterial Blood Gas (ABG) Test
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Lab Tests

Arterial Blood Gas (ABG) Test

An arterial blood gas (ABG) test measures the levels of oxygen and carbon dioxide in your blood to evaluate how well your lungs and kidneys are functioning.

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 oxygen measurement indicates how well your lungs move oxygen from the air into your blood, while the carbon dioxide measurement shows how well your lungs remove CO2 from your blood. Unlike most blood tests that use a vein, this test draws blood from an artery, which carries oxygen-rich blood from the heart and lungs to the body.

An ABG test typically includes the following measurements:

  • Oxygen saturation (O2 Sat): Measures how much oxygen your red blood cells are carrying.
  • Partial pressure of oxygen (PaO2): Measures the pressure of oxygen dissolved in your blood.
  • Partial pressure of carbon dioxide (PaCO2): Measures the amount of carbon dioxide, an acidic waste product, in your blood.
  • Acid-base balance (pH level): Measures the acidity of your blood. Imbalances can lead to acidosis (too much acid) or alkalosis (too much base/alkaline), which can be life-threatening.
  • Bicarbonate (HCO3): An electrolyte that helps control fluid and pH balance; it is the form in which most carbon dioxide is stored in the blood.

What is it used for?

The ABG test is used to:

  • Diagnose serious lung and breathing problems.
  • Diagnose kidney disorders, which also help regulate pH balance.
  • Monitor the effectiveness of treatments for breathing disorders, kidney disease, or acid-base imbalances.

Why do I need an arterial blood gas (ABG) test?

You may need this test if you exhibit symptoms of acid-base imbalances or are being treated for specific conditions:

  • Symptoms of acidosis: Rapid/deep breathing, arrhythmia, confusion, or fatigue.
  • Symptoms of alkalosis: Confusion, nausea, vomiting, muscle twitching/cramps, numbness in extremities or face, or arrhythmia.
  • Lung conditions: Asthma, chronic obstructive pulmonary disease (COPD), cystic fibrosis, or myasthenia gravis.
  • Other concerns: Carbon monoxide poisoning, inhalation injury, recent head or neck injury, or while receiving oxygen therapy in a hospital.

What happens during an arterial blood gas test?

The sample is usually taken from an artery in the wrist, though the arm or groin may be used. For newborns, the sample may be taken from the heel or umbilical cord. If taken from the wrist, the provider will first test your circulation by applying pressure to the arteries to ensure blood flow returns properly. A needle is then used to collect blood, and pressure is applied to the site for at least 5 minutes afterward to stop bleeding.

Will I need to do anything to prepare for the test?

Inform your provider of all medications and supplements you take, as some may affect acid-base balance or require you to stop taking blood thinners (including aspirin). If you are on oxygen therapy, it may be turned off for approximately 20 minutes before the test, provided you can breathe without it.

Are there any risks to the test?

Risks are minimal but include bleeding, bruising, or soreness at the puncture site. Rarely, the needle may damage a nerve or the artery. You may be advised to avoid lifting heavy objects for 24 hours following the procedure.

What do the results mean?

Because ABG results involve multiple body systems, your provider must interpret them in the context of your overall health. Normal ranges generally include:

  • Oxygen saturation (O2Sat): 95-100%
  • Partial pressure of oxygen (PaO2): 75-100 mmHg
  • Partial pressure of carbon dioxide (PaCO2): 35-45 mmHg
  • Acid-base balance (pH level): 7.35-7.45
  • Bicarbonate (HCO3): 22-26 mEq/L

Abnormal results may indicate lung or kidney issues or a metabolic disorder. Your provider will likely order follow-up tests if results are abnormal.

Is there anything else I need to know?

Pulse oximetry is another test that uses a clip-like device on your finger to check blood oxygen saturation. It may be used if blood oxygen levels are the only concern.

Frequently Asked Questions

pulse oximeter only measures the percentage of hemoglobin saturated with oxygen and cannot distinguish between low oxygen levels caused by lung failure versus low levels caused by anemia or carbon monoxide poisoning. An ABG test provides a comprehensive picture, including the partial pressure of oxygen (PaO2), the partial pressure of carbon dioxide (PaCO2), and the blood pH. This allows clinicians to assess ventilation (how well you are blowing off CO2) and acid-base status, which are critical for adjusting ventilator settings or oxygen flow rates in acute care settings.
You can generally eat and drink normally before an ABG test unless you are fasting for other concurrent blood work. However, smoking significantly affects the results by increasing carbon monoxide levels, which binds to hemoglobin and reduces its oxygen-carrying capacity. If you are a smoker, inform your provider, as they may interpret the oxygen saturation differently. Additionally, if you are receiving supplemental oxygen, the exact flow rate and duration of use must be documented at the time of the draw, as this directly impacts the PaO2 value and the clinical interpretation of your lung function.
While complications are rare, patients should monitor the puncture site for signs of excessive bleeding, expanding bruising, or a pulsating mass (pseudoaneurysm). More critically, if the test was performed on the wrist, watch for signs of arterial insufficiency in the hand, such as the fingers turning pale or blue, feeling cold, or experiencing numbness and tingling. If you notice any of these symptoms, or if bleeding does not stop after 15 minutes of firm pressure, seek immediate medical care to prevent tissue damage or infection.
n ABG test is generally more uncomfortable than a standard venipuncture because it involves puncturing an artery, which is deeper and under higher pressure. The procedure is often performed on the wrist (radial artery) or elbow (brachial artery). Patients typically feel a sharp pinch followed by a throbbing sensation. Recovery involves applying firm pressure to the site for 5 to 10 minutes to prevent bleeding. Most people can resume normal activities immediately, but they should avoid heavy lifting or straining with that arm for 24 hours to minimize the risk of hematoma formation.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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