CO2 blood test: MedlinePlus Medical Encyclopedia

P CO2 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.
P 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.

T How the Test is Performed
P 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.

T How to Prepare for the Test
P 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.

T How the Test will Feel
P 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.

T Why the Test is Performed
P 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 fluid. This may cause an imbalance in your body's electrolytes.
P CO2 levels in the blood are affected by kidney and lung function. The kidneys help maintain the normal bicarbonate levels.

T Normal Results
P The normal range is 23 to 29 milliequivalents per liter (mEq/L) or 23 to 29 millimoles per liter (mmol/L).
P Normal value ranges may vary slightly among different laboratories. Talk to your provider about the meaning of your specific test results.
P The example above shows the common measurement range of results for these tests. Some laboratories use different measurements or may test different specimens.

T What Abnormal Results Mean
P Abnormal levels may be due to the following problems:
P Lower-than-normal levels
- Addison disease
- Diarrhea
- Ethylene glycol poisoning
- Ketoacidosis
- Kidney disease
- Lactic acidosis
- Metabolic acidosis
- Methanol poisoning
- Salicylate toxicity (such as aspirin overdose)
P Higher-than-normal levels
- Breathing disorders
- Cushing syndrome
- Hyperaldosteronism
- Vomiting
P The following conditions may also alter bicarbonate levels:
- Alkalosis
- Delirium
- Dementia
- Renal tubular acidosis; distal
- Renal tubular acidosis; proximal

T Alternative Names
P Bicarbonate test; HCO3-; Carbon dioxide test; TCO2; Total CO2; CO2 test - serum; Acidosis - CO2; Alkalosis - CO2

T References
P Robinson MT, Heffner AC. Acid-base disorders. In: Adams JG, ed. Emergency Medicine. 2nd ed. Philadelphia, PA: Elsevier Saunders; 2013:chap 160.
P Seifter JL. Acid-base disorders. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 118.

T Review Date 5/21/2017
P Updated by: Laura J. Martin, MD, MPH, ABIM Board Certified in Internal Medicine and Hospice and Palliative Medicine, Atlanta, GA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

