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Carbon Dioxide Combining Power Blood Test

Last updated Jan. 25, 2016

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

  • CO2 Combining Power Blood Test

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

  • Carbon dioxide (CO2) combining power is the readiness with which CO2 combines with blood. It is used to estimate the acid-base balance in the body and the buffering capacity of blood
  • CO2 is released by cells as a waste product during metabolism. It gets absorbed by red blood cells and converted to carbonic acid (H2CO3). In this form, carbon dioxide is carried to the lungs for excretion (exhalation)
  • Carbon dioxide plays an important role as a buffer while in the form of carbonic acid. This means that it helps stabilize 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, it may result in widespread health issues
  • An acid and base react together to form water, which is called neutralization. Carbonic acid exists in an equilibrium between bicarbonate (HCO3-, a base) and hydronium (H+, an acid). If levels of acid in blood increase, carbonate neutralizes it; if levels of base increase, hydronium neutralizes it
  • The Carbon Dioxide Combining Power Blood Test helps determine the carbon dioxide combining power of blood. It helps diagnose metabolic acidosis or metabolic alkalosis

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

Following are the clinical indications for performing the Carbon Dioxide Combining Power 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 Carbon Dioxide Combining Power Blood Test?

Following is the specimen collection process for Carbon Dioxide Combining Power 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 Carbon Dioxide Combining Power Blood Test Result?

Following is the significance of the Carbon Dioxide Combining Power Blood Test:

  • A high value for the test may indicate:
    • Metabolic alkalosis
    • Gastric suction
    • Peptic ulcer
    • Hypothyroidism
    • Potassium deficit
    • Emphysema 
  • A low value for the 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 Carbon Dioxide Combining Power Blood Test. These include diet, exercise, and one’s 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.

What are some Useful Resources for Additional Information?

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:

Kee, J. L. (2010). Laboratory and diagnostic tests with nursing implications (8th ed.). Upper Saddle River, NJ: Pearson.

Lab Tests Online (2013, October 25). Retrieved July 24, 2014 from http://labtestsonline.org/understanding/analytes/electrolytes/

Martini, F., Nath, J. L., & Bartholomew, E. F. (2012). Fundamentals of anatomy & physiology (9th ed.). San Francisco: Benjamin Cummings.

Schnell, Z. B., Van, L. A., & Kranpitz, T. R. (2003). Davis's Comprehensive handbook of laboratory and diagnostic tests: With nursing implications. Philadelphia: F.A. Davis. 

Williamson, M. A., Snyder, L. M., & Wallach, J. B. (2011). Wallach's interpretation of diagnostic tests (9th ed.). Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins.

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Jan. 25, 2016
Last updated: Jan. 25, 2016