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Total Carbon Dioxide Blood Test

Last updated May 13, 2019

Approved by: Krish Tangella MD, MBA, FCAP

The Total Carbon Dioxide Blood Test determines the levels of carbon dioxide, bicarbonate, carbonate, and carbonic acid in blood.

What are other Names for this Test? (Equivalent Terms)

  • Total CO2 Levels Blood Test

What is the Total Carbon Dioxide Blood Test? (Background Information)

  • Total carbon dioxide (CO2) is a measure that includes carbon dioxide, bicarbonate (HCO3-), carbonate (CO32-), and carbonic acid (H2CO3-). The vast majority of carbon dioxide is present as bicarbonate
  • CO2 is released by cells as a waste product during metabolism. It gets absorbed by red blood cells and converted to carbonic acid by the enzyme carbonic anhydrase. In this form, carbon dioxide is carried to the lungs for excretion
  • Carbon dioxide plays an important role as a buffer while in the form of carbonic acid. This means that it helps stabilize the blood against rapid changes in acidity or basicity
  • Blood pH must remain between 7.2 and 7.6. If levels fall above or below this range, even slightly, widespread problems may result
  • An acid and base react together to form water. This is called neutralization. Carbonic acid exists in an equilibrium between carbonate (a base) and hydronium (H+, an acid). If levels of acid in the blood increase, carbonate neutralizes them and if levels of base increase, hydronium neutralizes them
  • The Total Carbon Dioxide Blood Test determines the levels of carbon dioxide, bicarbonate, carbonate, and carbonic acid in blood. It helps diagnose metabolic acidosis or metabolic alkalosis

What are the Clinical Indications for performing the Total Carbon Dioxide Blood Test?

Following are the clinical indications for performing the Total Carbon Dioxide Blood Test:

  • Monitoring the effects of diuretic drugs
  • Abnormal blood pressure
  • Muscle twitches and spasms
  • Muscle fatigue
  • Nausea, vomiting, diarrhea
  • Abnormal heart rhythms
  • Large changes in the amount of urine produced
  • Significant trauma and/or blood loss
  • Altered mental status

How is the Specimen Collected for the Total Carbon Dioxide Blood Test?

Following is the specimen collection process for Total Carbon Dioxide Blood Test:

Sample required: Blood

Process of obtaining blood sample in adults:

  • A band is wrapped around the arm, 3-4 inches above the collection site (superficial vein that lies within the elbow pit)
  • The site is cleaned with 70% alcohol in an outward spiral, away from the zone of needle insertion
  • The needle cap is removed and is held in line with the vein, pulling the skin tight
  • With a small and quick thrust, the vein is penetrated using the needle
  • The required amount of blood sample is collected by pulling the plunger of the syringe out slowly
  • The wrap band is removed, gauze is placed on the collection site, and the needle is removed
  • The blood is immediately transferred into the blood container, which has the appropriate preservative/clot activator/anti-coagulant
  • The syringe and the needle are disposed into the appropriate “sharp container” for safe and hygienic disposal

Preparation required: No special preparation is needed prior to the test.

What is the Significance of the Total Carbon Dioxide Blood Test Result?

The significance of the Total Carbon Dioxide Blood Test result is explained.

A low value for the Total Carbon Dioxide Blood Test may indicate:

  • Metabolic alkalosis
  • Gastric suction
  • Peptic ulcer
  • Hypothyroidism
  • Potassium deficit
  • Emphysema

A high value for the Total Carbon Dioxide Blood Test may indicate:

  • Metabolic acidosis
  • Diabetic ketoacidosis
  • Shock
  • Acute renal failure
  • Salicylate toxicity

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

  • Certain factors may interfere with the Total Carbon Dioxide Blood Test. These include diet, exercise, and hydration status

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider of the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

The following DoveMed website links are useful resources for additional information: 




Please visit our Laboratory Procedures Center for more physician-approved health information:


References and Information Sources used for the Article:

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Jan. 13, 2016
Last updated: May 13, 2019