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Arterial Blood Gases

Results

An arterial blood gas (ABG) test measures the acidity (pH) and levels of oxygen and carbon dioxide in the blood.

Normal

The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab and depend upon the elevation above sea level. Your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Results are usually available right away.

Arterial blood gases (at sea level and breathing room air) 1
Partial pressure of oxygen (PaO2):

Greater than 80 mm Hg (greater than 10.6 kPa)

Partial pressure of carbon dioxide (PaCO2):

35–45 mm Hg (4.6–5.9 kPa)

pH:

7.35–7.45

Bicarbonate (HCO3):

22–26 mEq/L (22–26 mmol/L)

Oxygen content (O2CT):

15–22 mL per 100 mL of blood (6.6–9.7 mmol/L)

Oxygen saturation (O2Sat):

95%–100% (0.95–1.00)

The concentration of oxygen being breathed, called the fraction of inhaled oxygen (FiO2), is also usually reported. This is only useful if you are receiving oxygen therapy from a tank or are on a ventilator.

Many conditions can change blood gas levels. Your doctor will talk with you about any abnormal results that may be related to your symptoms and past health.

What Affects the Test

Reasons you may not be able to have the test or why the results may not be helpful include the following:

  • You have a fever or an abnormally low body temperature (hypothermia).
  • You have a disease that affects how much oxygen is carried in your blood, such as severe anemia or polycythemia.
  • You smoke just before the test or breathe secondhand smoke, carbon monoxide, or certain paint or varnish removers in closed or poorly ventilated areas.

What To Think About

  • Arterial blood gas (ABG) values alone don't provide enough information to diagnose a problem. For example, they can't tell whether low levels are caused by lung or heart problems. Arterial blood gas values are most helpful when they are reviewed with other examinations and tests.
  • An ABG test is often done for a person who is in the hospital because of severe injury or illness. The test can measure how well the person's lungs and kidneys are working and how well the body is using energy.
  • An ABG test may be most useful when a person's breathing rate is increased or decreased or when the person has very high blood sugar (glucose) levels, a severe infection, or heart failure.
  • If several blood samples are needed, a thin tube (arterial catheter) may be placed in an artery. Blood can then be collected when needed.

WebMD Medical Reference from Healthwise

Last Updated: May 30, 2012
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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