An arterial blood gas (ABG) test measures the acidity (pH) and the levels of oxygen and carbon dioxide in the blood from an artery. This test is used to check how well your lungs are able to move oxygen into the blood and remove carbon dioxide from the blood.
As blood passes through your lungs, oxygen moves into the blood while carbon dioxide moves out of the blood into the lungs. An ABG test uses blood drawn from an artery, where the oxygen and carbon dioxide levels can be measured before they enter body tissues. An ABG measures:
- Partial pressure of oxygen (PaO2). This measures the pressure of oxygen dissolved in the blood and how well oxygen is able to move from the airspace of the lungs into the blood.
- Partial pressure of carbon dioxide (PaCO2). This measures the pressure of carbon dioxide dissolved in the blood and how well carbon dioxide is able to move out of the body.
- pH. The pH measures hydrogen ions (H+) in blood. The pH of blood is usually between 7.35 and 7.45. A pH of less than 7.0 is called acid and a pH greater than 7.0 is called basic (alkaline). So blood is slightly basic.
- Bicarbonate (HCO3). Bicarbonate is a chemical (buffer) that keeps the pH of blood from becoming too acidic or too basic.
- Oxygen content (O2CT) and oxygen saturation (O2Sat) values. O2 content measures the amount of oxygen in the blood. Oxygen saturation measures how much of the hemoglobin in the red blood cells is carrying oxygen (O2).
Blood for an ABG test is taken from an artery. Most other blood tests are done on a sample of blood taken from a vein, after the blood has already passed through the body's tissues where the oxygen is used up and carbon dioxide is produced.
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) |
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| Partial pressure of carbon dioxide (PaCO2): | 35-45 mm Hg (4.6-5.9 kPa) |
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| pH: | 7.35-7.45 |
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| Bicarbonate (HCO3): | 22-26 mEq/L (22-26 mmol/L) |
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| Oxygen content (O2CT): | 15-22 mL per 100 mL of blood (6.6-9.7 mmol/L) |
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| Oxygen saturation (O2Sat): | 95%-100% (0.95-1.00) |
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The normal values for children may differ from the adult values listed here.
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.
I requested an ABG from my General Practitioner so that I would have a baseline measure of my blood gases and could later compare new numbers with the baseline. I did this so that my Health Care Team could have a good indication of decline which will happen as the disease progresses.
It was a little painful but nothing compared with going to the dentist!
