What Is a Normal Co2 Level in the Body

Carbon dioxide is in the air, in the ocean, and even in soda. You can also find carbon dioxide in your blood, where it plays an important role in regulating your breathing and maintaining the pH of your blood. Learn about the different ways to test carbon dioxide levels and what the results mean.

What is Carbon Dioxide?

Carbon dioxide, which has the chemical formula CO₂, is a gas that is naturally found in the Earth's atmosphere and the human body. When cells convert sugars and fats into energy, they create CO₂ as a byproduct. This CO₂ then travels through the blood and into the lungs, where it is exhaled out of the body [1].

Most of the CO₂ in the body (usually over 90%) is actually in the form of bicarbonate (HCO_3- ). The rest is dissolved in the blood or found in the form of carbonic acid (H₂CO₃). CO₂ naturally switches between these different forms depending on how acidic or basic the blood is, otherwise known as blood pH [1, 2].

CO₂, especially in the form of bicarbonate, plays an important role in maintaining the pH of the blood. Bicarbonate acts as a buffer, preventing blood from becoming too acidic or basic [3].

The breathing rate is also regulated by CO₂. A high level of CO₂ in the blood tells the body that it's not getting enough oxygen, which will trigger the urge to breathe [4].

The body creates CO₂ as a byproduct of energy production. It helps maintain blood pH and regulates breathing.

Why test CO₂ levels?

CO₂ levels are most commonly used to evaluate the acid-base balance in the blood, which may be disturbed by issues in the lungs or kidneys. Three pieces of information are needed to get a full picture of acid-base status, which include [1]:

• Blood pH, which is based on the concentration of hydrogen ions in the blood. Hydrogen ions are released when an acid reacts with water and is a marker for acidity.
• Bicarbonate (HCO_3-), the most common form of CO₂ in your body. It plays an important role in maintaining blood pH.
• Partial pressure of CO₂ (pCO₂), which represents the pressure that CO₂ gas exerts in the blood.

Besides acid-base balance, CO₂ levels are also helpful in monitoring lung diseases and the effectiveness of oxygen therapy [1].

Testing CO₂ levels can reveal acid-base imbalances in the blood that may be due to lung or kidney problems.

Carbon Dioxide (CO₂) Blood Test

Test Types

There are several different tests that measure CO₂ levels in the blood. Each test measures a different form or aspect of CO₂ and sometimes multiple tests are needed to get a full picture of an individual's health.

Total Carbon Dioxide Test

The serum total carbon dioxide test (TCO₂ test) measures the total amount of CO₂ (in all forms) in the blood, including [1]:

• CO₂ bound to other compounds
• HCO_3-
• H₂CO₃.

This test requires a blood sample, which a medical professional will usually take from a vein in the arm [1].

The TCO₂ test does not measure the components typically used to evaluate acid-base balance (blood pH, HCO_3-, and pCO₂ are what is needed) [1].

However, since so much of a person's CO₂ is in the form of HCO_3-, the total CO₂ is often used as a surrogate for HCO_3- levels. In fact, the terms CO₂ and HCO_3- are sometimes used interchangeably in terms of these tests [1].

Because the TCO₂ test is fairly quick and easy to perform, it is usually the first test used to screen for acid-base disorders. If results are abnormal, additional tests may be performed [1].

The total carbon dioxide test estimates HCO_3- levels and is used to screen for acid-base imbalances.

Arterial Blood Gas Test

The arterial blood gas (ABG) test is also commonly performed. It measures pCO₂, pO₂, and blood pH. In addition, it is possible to calculate HCO_3- levels using the results of this test. This means the ABG test provides all the information needed to fully evaluate acid-base balance [5].

The ABG test is also a little more difficult to perform compared to other tests. This test requires a blood sample from the artery, which can be more painful and potentially has more complications compared to drawing blood from the veins [1, 6].

Despite being harder to perform, the ABG test is still one of the best ways to evaluate blood pH imbalances and is commonly performed whenever an acid-base disorder is suspected [1, 6].

The arterial blood gas gives the most complete picture of acid-base status in a patient.

Bicarbonate Test

The bicarbonate test measures only the amount of HCO_3- in the blood using samples from the veins. It is less commonly used than the ABG test because it provides less information. However, a venous HCO_3- test is also easier and cheaper to perform than an ABG test, making it sometimes more popular in rural areas or less developed countries [1, 6].

CO₂ tests are used to evaluate the acid-base balance in the blood or lung issues.

Carbon Dioxide (CO₂) Normal Levels

Normal ranges can vary between laboratories due to differences in equipment, techniques, and chemicals used. If your results are outside of the normal range, it may not necessarily mean there is something wrong. However, a normal result also doesn't mean a particular medical condition is absent. Always talk with your doctor to learn more about your test results.

By Test Type

For total CO₂ in the blood, the normal range is about 23 to 30 mEq/L [2].

For HCO_3- in the blood, the normal range is about 22 to 26 mEq/L [7].

For pCO₂ in the arteries, the normal range is about 35 to 45 mmHg [7].

However, these ranges can vary depending on many factors, such as [1]:

• Gender: men usually have slightly higher CO₂ levels than women
• Blood sample source: venous blood has slightly higher CO₂ levels than arterial blood
• Altitude: higher elevations may lower CO₂ levels

Learn More

This post is part of a three-part series about carbon dioxide. Read the other parts to learn about:

• Carbon dioxide poisoning and the causes & risks of high CO₂ levels
• The causes & risks of low CO₂ levels

Takeaway

Carbon dioxide (CO₂) blood tests are normally used to evaluate issues with your breathing or imbalances in your blood pH. Many factors can affect your CO₂ levels, most of which stem from kidney and lung disorders. Correcting an abnormal CO₂ level usually involves treating the underlying condition that is causing the imbalance.

What Is a Normal Co2 Level in the Body

Source: https://labs.selfdecode.com/blog/carbon-dioxide-co2/

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