Illness and Conditions - Medical Tests
Carbon Dioxide (Bicarbonate)
Carbon dioxide (CO2) is a gaseous waste product from metabolism . The blood carries carbon dioxide to your lungs, where it is exhaled. More than 90% of carbon dioxide in your blood exists in the form of bicarbonate (HCO3). The rest of the carbon dioxide is either dissolved carbon dioxide gas (CO2) or carbonic acid (H2CO3). Your kidneys and lungs balance the levels of carbon dioxide, bicarbonate, and carbonic acid in the blood.
This test measures the level of bicarbonate in a sample of blood from a vein. Bicarbonate is a chemical (buffer) that keeps the pH of blood from becoming too acidic or too basic.
Bicarbonate is not usually tested by itself. It may be done on a blood sample taken from a vein as part of a panel of tests that looks at other electrolytes , such as sodium, potassium, and chloride. It can also be done as part of an arterial blood gas (ABG) test. For the arterial blood gas study, the blood sample is taken from an artery.
Why It Is Done
A carbon dioxide (bicarbonate) test helps find and keeps track of conditions that affect blood bicarbonate levels, including many kidney diseases, some lung diseases, and metabolic conditions.
It is often done as part of a group of laboratory blood tests (chemistry screen) to help find the cause of many kinds of symptoms.
How To Prepare
You do not need to do anything before you have this test.
Many medicines may change the results of this test. Be sure to tell your doctor about all the nonprescription and prescription medicines you take.
Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results may mean. To help you understand the importance of this test, fill out the medical test information form (What is a PDF document?) .
How It Is Done
The health professional drawing blood will:
How It Feels
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
There is very little risk of complications from having blood drawn from a vein.
A carbon dioxide (bicarbonate) test measures the level of bicarbonate in the blood.
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and 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 in 1 to 2 days.
High carbon dioxide (bicarbonate) levels may be caused by:
Low carbon dioxide (bicarbonate) levels may be caused by:
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:
What To Think About
Last Revised: May 30, 2012
Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.
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