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How Does an Arterial Blood Gas (ABG) Study Work? What Does it Test?

An arterial blood gas (ABG) study is a blood test that measures the acidity, or pH of your blood, as well as your oxygen (O2) and carbon dioxide (CO2) levels. The test is used to evaluate the function of your lungs and how well they’re able to move oxygen into your blood while removing carbon dioxide, the waste product of respiration.[1]

When Should an ABG be Ordered?

abg study, Arterial Blood Gas Study, How Does an Arterial Blood Gas Study WorkThere are a number of reasons why your doctor may order an ABG. They include, but are not limited to:1

  • COPD exacerbation
  • Respiratory failure
  • Kidney failure
  • Shock
  • Trauma
  • Uncontrolled diabetes
  • Asthma
  • Hemorrhage
  • Drug overdose
  • Chemical poisoning

Key Components of an ABG Study

The components listed below represent the key features of an arterial blood gas (ABG) study. Each element has a different normal value and represents important aspects of a blood gas. The National Institute of Health reports the typical normal values below:1

  • pH: normal values range from 35 to 7.45. The pH of any fluid represents the measure of hydrogen ion (H) concentration in that fluid. The lower the pH, the more acidic the blood. The higher the pH, the more alkaline the blood.
  • Partial pressure of oxygen (PaO2): normal values range from 75 to 100 mmHg. PaO2 is a measure of oxygen in arterial blood.
  • Partial pressure of carbon dioxide (PaCO2): normal values range from 35 to 45 mmHg. PaCO2 is a measure of carbon dioxide in arterial blood.
  • Bicarbonate (HCO3): normal values range from 22 to 26 mEq/L. HCO3 is a measure of the amount of bicarbonate in your blood. Your blood brings bicarbonate to your lungs, which is then exhaled as carbon dioxide. A high level of bicarbonate in your blood may cause a condition known as metabolic alkalosis. A low level of bicarbonate in your blood may lead to a condition known as metabolic acidosis.
  • Oxygen saturation (SaO2): normal values vary between 95 to 100 percent. SaO2 represents the percentage of oxygen molecules in the blood that are saturated with hemoglobin. An estimate of oxygen saturation can also be done using a pulse oximeter, a small probe that attaches to the end of your finger.

How the Test is Performed

Many times, ABGs are drawn in the hospital, but they can also be drawn in your doctor’s office. The blood used for the test is usually drawn from the radial artery in your wrist, but it can also be drawn from an artery in your forearm or groin.[2]

Before the test, your doctor or other qualified health care practitioner may perform a modified Allen test, whereby pressure is applied to the arteries in your wrist for several seconds. This test checks to see if blood flow to your hand is within normal limits.2

Your doctor or other qualified health care practitioner will use a small needle when drawing the blood. You’re likely to experience more discomfort during this test than you would in the course of a regular blood draw from a vein, because arteries run deeper than veins and there are sensitive nerves in the underside of the wrist surrounding the insertion site. You may also feel lightheaded, faint, dizzy or nauseated during the procedure, but the test only lasts a few minutes and your discomfort should ease once it’s over.2

What the Results Mean

Your test results should be ready in as little as 15 minutes. Once your doctor reviews the results, she may order additional tests to help her formulate a diagnosis. Your test results will tell your doctor whether your lungs are getting enough oxygen, whether they’re removing enough carbon dioxide and whether your kidneys are functioning properly. If your arterial blood gas (ABG) study is abnormal, your doctor will consider the results, along with the results of your other tests. Only then will she be able to recommend a proper treatment plan moving forward.

For more information about having an arterial blood gas (ABG) study, talk to your primary care provider or hospitalist.

[1] Colduvell, Kathleen, RN, BSN, BA, CBC. Know Your ABGs: Arterial Blood Gases Explained. October 26, 2017.

[2] WebMD. What is an Arterial Blood Gas? Last reviewed October 4, 2017.


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