CO2 blood test
Bicarbonate test; HCO3-; Carbon dioxide test; TCO2; Total CO2; CO2 test - serum; Acidosis - CO2; Alkalosis - CO2CO2 is carbon dioxide. This article discusses the laboratory test to measure the amount of carbon dioxide in the liquid part of your blood, called the serum.
In the body, most of the CO2 is in the form of a substance called bicarbonate (HCO3-). Therefore, the CO2 blood test is really a measure of your blood bicarbonate level.
How the Test is Performed
A blood sample is needed. Most of the time, blood is drawn from a vein located on the inside of the elbow or the back of the hand.
Blood is drawn from a vein
Venipuncture is the collection of blood from a vein. It is most often done for laboratory testing.
How to Prepare for the Test
Many medicines can interfere with blood test results.
- Your health care provider will tell you if you need to stop taking any medicines before you have this test.
- DO NOT stop or change your medicines without talking to your provider first.
How the Test will Feel
You may feel slight pain or a sting when the needle is inserted. You may also feel some throbbing at the site after the blood is drawn.
Why the Test is Performed
The CO2 test is most often done as part of an electrolyte or basic metabolic panel. Changes in your CO2 level may suggest that you are losing or retaining acidic fluid. This may cause an imbalance in your body's electrolytes.
Electrolyte
Electrolytes are minerals in your blood and other body fluids that carry an electric charge. Electrolytes affect how your body functions in many ways...
CO2 levels in the blood are affected by kidney and lung function. The kidneys help maintain the normal bicarbonate levels.
Normal Results
The normal range is 23 to 29 milliequivalents per liter (mEq/L) or 23 to 29 millimoles per liter (mmol/L).
Normal value ranges may vary slightly among different laboratories. Talk to your provider about the meaning of your specific test results.
The example above shows the common measurement range of results for these tests. Some laboratories use different measurements or may test different specimens.
What Abnormal Results Mean
Abnormal levels may be due to the following problems:
Lower-than-normal levels:
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Addison disease
Addison disease
Addison disease is a disorder that causes the adrenal glands to not produce enough hormones.
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- Diarrhea
- Ethylene glycol poisoning
-
Ketoacidosis
Ketoacidosis
Diabetic ketoacidosis (DKA) is a life-threatening problem that affects people with diabetes. It occurs when the body starts breaking down fat at a r...
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- Lactic acidosis
Acidosis
Acidosis is a condition in which there is too much acid in the body fluids. It is the opposite of alkalosis (a condition in which there is too much ...
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Metabolic acidosis
Metabolic acidosis
Metabolic acidosis is a condition in which there is too much acid in the body fluids.
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- Renal tubular acidosis -- distal
- Renal tubular acidosis -- proximal
- Respiratory alkalosis (compensated)
- Salicylate toxicity (such as aspirin overdose)
- Ureteral diversion
Higher-than-normal levels:
- Bartter syndrome
- Burns
- Congestive heart failure
-
Cushing syndrome
Cushing syndrome
Cushing syndrome is a disorder that occurs when your body has a high level of the hormone cortisol.
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- Excessive sweating
-
Hyperaldosteronism
Hyperaldosteronism
Hyperaldosteronism is a disorder in which the adrenal gland releases too much of the hormone aldosterone into the blood. Hyperaldosteronism can be pr...
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- Respiratory acidosis (compensated)
- Syndrome of inappropriate diuretic hormone secretion (SIADH)
- Vomiting
Delirium may also alter bicarbonate levels.
Delirium
Delirium is sudden severe confusion due to rapid changes in brain function that can occur with physical or mental illness.
References
Bansal A. Respiratory acidosis, respiratory alkalosis, and mixed acid-base disorders. In: Johnson RJ, Floege J, Tonelli M, eds. Comprehensive Clinical Nephrology. 7th ed. Philadelphia, PA: Elsevier; 2024:chap 15.
Seifter JL. Acid-base disorders. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 110.
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Blood test - illustration
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. Preparation may vary depending on the specific test.
Blood test
illustration
-
Blood test - illustration
Blood is drawn from a vein (venipuncture), usually from the inside of the elbow or the back of the hand. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. Preparation may vary depending on the specific test.
Blood test
illustration
Review Date: 6/20/2023
Reviewed By: Jacob Berman, MD, MPH, Clinical Assistant Professor of Medicine, Division of General Internal Medicine, University of Washington School of Medicine, Seattle, WA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.
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