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Total CO2 or bicarbonate is different than the partial pressure of CO2 (PCO2). Learn about PCO2
The Test Sample
What is being tested?
Bicarbonate is an electrolyte, a negatively charged ion that is used by the body to help maintain the body's acid-base (pH) balance. It also works with the other electrolytes (sodium, potassium, and chloride) to maintain electrical neutrality at the cellular level. This test measures the total amount of carbon dioxide (CO2) in the blood, which occurs mostly in the form of bicarbonate (HCO3-). The CO2 is mainly a by-product of various metabolic processes.
Measuring bicarbonate as part of an electrolyte or metabolic panel may help diagnose an electrolyte imbalance or acidosis or alkalosis. Acidosis and alkalosis describe the abnormal conditions that result from an imbalance in the pH of the blood caused by an excess of acid or alkali (base). This imbalance is typically caused by some underlying condition or disease.
The lungs and kidneys are the major organs involved in regulating blood pH through the removal of excess bicarbonate.
- The lungs flush acid out of the body by exhaling CO2. Raising and lowering the respiratory rate alters the amount of CO2 that is breathed out, and this can affect blood pH within minutes.
- The kidneys eliminate acids in the urine and they regulate the concentration of bicarbonate (HCO3-, a base) in blood. Acid-base changes due to increases or decreases in HCO3- concentration occur more slowly than changes in CO2, taking hours or days.
Any disease or condition that affects the lungs, kidneys, metabolism, or breathing has the potential to cause acidosis or alkalosis.
The bicarbonate test gives a healthcare practitioner a rough estimate of a patient's acid-base balance. This is usually sufficient, but measurements of gases dissolved in the blood (blood gases) may be done if more information is needed. Bicarbonate is typically measured along with sodium, potassium, and possibly chloride in an electrolyte panel as it is the balance of these molecules that gives the healthcare practitioner the most information.
How is the sample collected for testing?
A blood sample is drawn by needle from a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.