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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 it in your blood exists in the form of bicarbonate (HCO3). The rest of it 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 that acts as a buffer. It keeps the
pH of blood from becoming too acidic or too
Bicarbonate is not usually tested by itself. The test may be done
on a blood sample taken from a vein as part of a panel of tests that looks at
electrolytes. These may include items such as sodium, potassium, and chloride.
It can also be done as part of an
arterial blood gas (ABG) test. For this blood
gas study, the blood sample comes from an artery.
A carbon dioxide test helps find and
checks conditions that affect blood bicarbonate levels. These include many
kidney diseases, some lung diseases, and
This test is often done as part of a group of lab blood tests (chemistry screen) to help find the cause of many kinds of symptoms.
You do not need to do anything special to prepare for this test.
Be sure to tell your doctor about all the medicines you take, even over-the-counter ones. Many medicines can change the results of this test.
Talk to your doctor if you have any concerns about
the need for the test, its risks, how it will be done, or what the results will
mean. To help you learn about this test and how important it is, fill out the
medical test information form(What is a PDF document?).
The health professional taking a sample of your blood will:
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 chance of a problem from having a blood sample taken from a vein.
A carbon dioxide (bicarbonate) test measures the
level of bicarbonate in the blood.
These numbers are just a guide. The range for "normal" varies from lab to lab. Your lab may have a different range. Your lab report should show what range your lab uses for "normal." Also, your doctor will evaluate your results based on your health and other factors. So a number that is outside the normal range here may still be normal for you.
Results are usually ready in 1 to 2 days.
High carbon dioxide (bicarbonate) levels may be caused
Low carbon dioxide (bicarbonate) levels may be caused
You may not be able to have the test, or the results may not be helpful, if:
Fischbach F, Dunning MB III (2015). A Manual of Laboratory and Diagnostic Tests, 9th ed. Philadelphia: Wolters Kluwer Health.
Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.
Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby Elsevier.
ByHealthwise StaffPrimary Medical ReviewerE. Gregory Thompson, MD - Internal MedicineAdam Husney, MD - Family MedicineSpecialist Medical ReviewerRobert L. Cowie, MB, FCP(SA), MD, MSc, MFOM - Pulmonology
Current as ofApril 3, 2017
Current as of:
April 3, 2017
E. Gregory Thompson, MD - Internal Medicine
& Adam Husney, MD - Family Medicine & Robert L. Cowie, MB, FCP(SA), MD, MSc, MFOM - Pulmonology
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