Blood Gas Test

Written by Rachel Nall | Published on July 18, 2012
Medically Reviewed by Brenda B. Spriggs, MD, MPH, FACP

Overview

Your red blood cells transport oxygen and carbon dioxide — blood gases — throughout the body. The oxygen and carbon dioxide levels of your blood and the pH balance of your blood can indicate the presence of certain medical conditions, such as cardiac, lung or kidney disorders and the presence or status of other critical conditions such as:

  • uncontrolled diabetes
  • hemorrhage
  • drug overdose
  • shock

Your physician may order a test known as a blood gas analysis or arterial blood gas (ABG) test to determine your levels. This test requires collecting a small amount of blood from an artery and reading the results within 10 minutes.

What Are the Uses of a Blood Gas Test?

While your oxygen and breathing levels can indicate to your physician how oxygenated your blood is, a blood gas analysis provides a more precise measurement.

Knowing your blood’s pH balance and oxygen and carbon dioxide levels helps your doctor understand how well your lungs and kidneys function. Identifying imbalances in your pH and blood gas levels can provide an early warning about how your body is handling illness.

Your physician may order a blood gas analysis if he or she suspects you are experiencing any of the following conditions:

  • lung disease
  • kidney disease
  • metabolic disease
  • head or neck injuries that affect breathing

How Is a Blood Gas Test Performed?

An ABG test requires obtaining a 2 ml sample of blood. This blood can be obtained from an artery in your wrist, arm, or groin. A medical provider will first apply an alcohol or antiseptic swab to your skin, and then use a needle to draw blood.

The blood sample will be analyzed via a portable machine or in an on-site laboratory. To get the best test result, the test must be analyzed within 10 minutes of drawing blood.

Interpreting the Results of a Blood Gas Test

The arterial blood gas test returns several key results, which can aid in diagnosing a condition as well as determining how well certain treatments are working for your body (such as treatment for lung diseases).

One result that an arterial blood gas test provides is pH balance. The typical pH balance for your blood is 7.38 to 7.42. If your blood pH is lower than 7.38, it is more acidic and has higher carbon dioxide levels. A blood pH higher than 7.42 may indicate that your blood is more basic or alkaline and has a higher bicarbonate level.

While the normal values at sea level may vary based on the lab testing the sample, normal values, according to the National Institutes of Health (NIH), include:

  • arterial blood pH: 7.38 to 7.42
  • partial pressure of oxygen (PaO2): 75 to 100 mmHg
  • partial pressure of carbon dioxide (PaCO2): 38 to 42 mmHg
  • oxygen saturation (SaO2): 94 to 100 percent
  • bicarbonate (HCO3): 22 to 28 mEq/L

If you live higher than sea level, your blood oxygen levels may be lower.

These results can indicate certain medical conditions., such as the ones in the table below. If your levels are off balance, your physician can recommend treatments, such as oxygen therapy, to get them back to normal.

Blood pH

Bicarbonate

PCO2

Condition

Common Causes

Less than 7.4

Low

Low

Metabolic acidosis

Kidney failure, shock,

diabetic ketoacidosis

Greater than 7.4

High

High

Metabolic alkalosis

Chronic vomiting, low blood potassium

Less than 7.4

High

High

Respiratory acidosis

Lung diseases, including pneumonia or COPD

Greater than 7.4

Low

Low

Respiratory alkalosis

Breathing too fast, pain or anxiety

What Are the Test’s Side Effects?

Because the test does not require a large sample of blood, it is considered low-risk. If you are dehydrated or have deep arteries, drawing blood may be more difficult. Always tell your physician if you have a medical condition that may affect bleeding or if you’re taking medications, such as blood thinners, that may cause you to bleed more than expected.

Side effects associated with the arterial blood gas test include:

  • bleeding or bruising at the puncture site
  • feeling faint
  • blood accumulating under the skin
  • infection at the puncture site

Notify your medical provider if you experience unexpected or prolonged side effects.

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