An arterial blood gas (ABG) test helps assess someone with chronic obstructive pulmonary disease (COPD). Not everyone with COPD needs the test, but doctors may use it in certain situations.

COPD is a progressive condition, which means that it typically worsens over time. Doctors must carefully manage COPD to help avoid complications and adverse effects.

This article explores the arterial blood gas (ABG) test, explaining what it is and why doctors may use it for people with COPD. It looks at what the test involves, how often a person needs it, and what the results mean. In addition, it answers some frequently asked questions.

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An ABG test assesses the partial pressures of gas in the blood and the acid-base content. Medical professionals may use an ABG test to evaluate someone’s lung function.

Research indicates that ABG testing is helpful for monitoring disease progression in chronic COPD.

Experts explain that, for the body to function properly, the lungs must take in an equal amount of oxygen to what the body tissues consume. Additionally, the amount of carbon dioxide that metabolism produces must be equal to the amount of carbon dioxide that the lungs get rid of.

Testing can reveal if these processes are not optimal or if respiratory failure is present. ABG tests measure the following values:

  • pH value
  • PaO2 — partial pressure of oxygen in arterial blood
  • PaCO2 — partial pressure of carbon dioxide in arterial blood

Doctors can use ABG test results to evaluate if someone with COPD has airflow limitations and if their condition is worsening.

For an ABG test, a doctor obtains a blood sample from an artery using a needle. They will typically take the sample from an artery in the wrist, but they can also take it from an artery in the arm or groin.

If someone is already in the hospital and doctors are monitoring them for a particular condition, they may obtain the blood through an arterial catheter.

Medical professionals place the blood on ice and often use automated blood analyzers to evaluate the sample.

A doctor may decide to give someone with COPD an ABG test if their signs and symptoms indicate that this may be useful.

For example, experts note that if someone has a significantly decreased forced expiratory volume and signs of dyspnea, they may need an ABG test. Forced expiratory volumeis the volume of air that a person can exhale during a forced breath in a certain number of seconds. Dyspnea refers to shortness of breath or not being able to get enough air.

Another situation in which doctors may decide to do an ABG test is when a person experiences a COPD exacerbation. This might include increased coughing and wheezing or a respiratory infection.

Additionally, doctors may use an ABG test before someone with COPD has anesthesia for surgery. They may also use the test to evaluate the individual after the operation.

Learn more about exacerbations of COPD.

A person’s doctor can provide them with information about anything specific they need to do to prepare for an ABG test.

If a person is taking certain medications, such as blood thinners, the doctor may advise stopping them before the test. However, a person should continue taking their medication unless their doctor advises otherwise.

If a person has oxygen therapy but is able to breathe without it, they may need to turn the oxygen off 20 minutes before the test. The medical professional performing the test can provide more information about this if it is relevant.

Doctors look at the results of an ABG test to interpret the findings in light of a person’s symptoms and condition.

Experts advise that acceptable ranges may vary among laboratories and age groups. The following is an example of a typical range of values:

  • pH: 7.35–.45
  • PaO2: 75–100 millimeters of mercury (mmHg)
  • PaCO2: 35–45 mmHg
  • HCO3: 22–26 milliequivalents per liter (meq/L)
  • Base excess/deficit: -4 to +2
  • SaO2: 95–100%

A person’s doctor can explain what their test results mean in more detail and answer any questions they may have.

The following answers some common questions about ABG tests.

How does COPD affect arterial blood gas?

Experts explain that, in people with COPD, pH and PaO2 levels decrease and PaCO2 levels increase. Using an ABG test to detect these changes can help monitor the condition’s progression.

Does COPD cause acidosis or alkalosis?

COPD can cause acidosis. Respiratory acidosis occurs when the lungs cannot properly remove carbon dioxide.

ABG tests can help doctors monitor the progression of COPD and evaluate exacerbations of the condition. They may also use an ABG test if someone with COPD requires surgery.

An ABG test involves a doctor taking a blood sample using a needle. A person can speak with a doctor to find out details about the procedure and what their test results mean.