Carbon Dioxide (CO2) is a natural byproduct of your body’s metabolism. As your body breaks down nutrients for energy, CO2 is produced and transported through the bloodstream—mostly in the form of bicarbonate (HCO3)—to the lungs, where it is exhaled. In healthy individuals, CO2 levels in the blood remain within a stable, normal range.
CO2 plays a critical role in maintaining your body's acid-base balance (pH). It acts as a buffer to keep your blood from becoming too acidic or too alkaline. As an electrolyte, CO2 works alongside other key electrolytes like sodium, potassium, and chloride to maintain cellular stability and fluid balance.
A CO2 blood test (also called a bicarbonate test, total CO2 test, or CO2 content test) measures the amount of carbon dioxide in your blood, primarily in the form of bicarbonate. This test helps assess your acid-base balance and electrolyte levels, and may indicate whether there is an underlying condition affecting your lungs, kidneys, or metabolic function.
Bicarbonate (HCO3) test
Total CO2 (TCO2)
CO2 content test
CO2 serum test
Carbon dioxide content
Maintaining the right level of carbon dioxide is essential for healthy body function. Abnormal CO2 levels—either too high or too low—can signal a range of health conditions such as:
Respiratory issues
Kidney dysfunction
Metabolic imbalances
Dehydration
Acidosis or alkalosis
The test is often part of a comprehensive metabolic panel (CMP) or electrolyte panel, which also checks sodium, potassium, and chloride levels.
Your healthcare provider may order a CO2 test if you’re experiencing symptoms of a pH imbalance or electrolyte disorder, including:
Shortness of breath
Nausea or vomiting
Fatigue
Breathing difficulties
CO2 levels may also be monitored regularly if you’re undergoing oxygen therapy, certain surgeries, or treatments for chronic lung or kidney conditions.
While they’re often used interchangeably, there is a subtle difference:
Bicarbonate (HCO3) is the main form of carbon dioxide in your blood.
The CO2 blood test actually measures total bicarbonate levels.
This is why the terms CO2 test and bicarbonate test usually refer to the same lab measurement.
Normal carbon dioxide levels in the blood typically range from:
20 – 29 milliequivalents per liter (mEq/L) for adults
However, what's considered "normal" can vary slightly by lab. A CO2 result outside the reference range does not always mean there’s a serious health issue—factors like dehydration, medications, or temporary illness may affect levels.
In some cases, your doctor may order an arterial blood gas (ABG) test to get more precise measurements of CO2, bicarbonate, pH, and oxygen levels. Unlike a standard blood test taken from a vein, an ABG sample is drawn from an artery and is particularly useful in evaluating lung function and respiratory conditions.
Too low or high bicarbonate levels can be associated with:
Metabolic acidosis (too much acid in the body)
Metabolic alkalosis (too much base)
Kidney disease
Liver failure
Diarrhea or vomiting
Chronic obstructive pulmonary disease (COPD)
Eating disorders like anorexia
Your healthcare provider will interpret your CO2 level alongside other test results and symptoms to identify the root cause.
The carbon dioxide (CO2) blood test is a quick and effective tool for assessing acid-base status and electrolyte balance in your body. It’s often part of broader metabolic testing and is especially important for people with respiratory, kidney, or metabolic concerns.
If your test results are outside the normal range, follow up with your doctor. The results must be interpreted in context, alongside other lab values and clinical symptoms.
University of Rochester Medical Center – Carbon Dioxide (Blood)
Kovesdy CP. Metabolic acidosis and kidney disease. Nephrol Dial Transplant. 2012.
Bijapur MB et al. Central Venous vs. Arterial Blood Gas Analysis. Indian J Crit Care Med. 2019.
Seifter JL, Chang HY. Disorders of Acid-Base Balance. Kidney Dis (Basel). 2017.
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If your comprehensive metabolic panel (CMP) shows an elevated level of carbon dioxide (CO2), it could mean there's an imbalance in your body's pH (acid-base) levels. CO2 in this test refers to bicarbonate (HCO3-), which helps keep your blood's pH stable. When CO2 levels are higher than normal, it may indicate certain health issues. Here's what you need to know:
Respiratory Issues
Problems with breathing can affect CO2 levels in your blood. For example:
Slow or shallow breathing (hypoventilation) may cause CO2 to build up in your blood.
Chronic respiratory conditions like COPD can also make it harder for your lungs to remove CO2.
Metabolic Alkalosis
This happens when there’s too much bicarbonate in your blood. Causes include:
Excessive vomiting (which removes stomach acid).
Dehydration or losing fluids for a long time.
Overuse of diuretics (medications that help remove excess water from your body).
Kidney Problems
Your kidneys play a big role in balancing bicarbonate and CO2 levels. If they aren’t working properly—like in chronic kidney disease—they might not remove enough bicarbonate, leading to higher CO2 levels.
Cushing's Syndrome
This condition occurs when your body produces too much cortisol, a hormone that can affect your CO2 levels.
Chronic Lung Conditions
Diseases like chronic obstructive pulmonary disease (COPD) or other lung issues can cause difficulty in removing CO2 from your blood.
If you have high CO2 levels, don’t panic! Elevated CO2 can be caused by many factors, and it’s important to work with your healthcare provider to figure out what’s going on. They might recommend additional tests or ask about symptoms like breathing problems, dehydration, or recent illnesses.
Here are some questions you can ask your doctor:
What could be causing my high CO2 levels?
Do I need more tests?
Are there lifestyle changes or treatments that can help?
An elevated carbon dioxide (CO2) level on a comprehensive metabolic panel (CMP) can indicate an imbalance in the body’s acid-base regulation, potentially pointing to conditions like respiratory or metabolic alkalosis, kidney dysfunction/failure, or respiratory disorders like COPD. The presence of high CO2 levels suggests that the body may be retaining too much bicarbonate, which can disrupt normal pH levels and impact overall health. Next steps should include further investigation by a healthcare provider to determine the root cause. This may involve additional tests such as arterial blood gas analysis, kidney function tests, or respiratory assessments. Treatment will depend on the underlying condition, ranging from managing respiratory function to addressing kidney health or electrolyte imbalances. It’s important to follow up with a healthcare professional to tailor an appropriate treatment plan.
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A low level of carbon dioxide (CO2) in the blood—typically referring to a low bicarbonate (HCO3) concentration—can result from various medical conditions and physiological imbalances. This can signal disruptions in your body's acid-base balance, often pointing to metabolic acidosis or respiratory alkalosis, depending on the pH level of your blood.
Several health conditions and situations can cause CO2 levels to drop:
Hyperventilation (rapid breathing that lowers CO2)
Aspirin (salicylate) or alcohol overdose
Diarrhea, dehydration, or severe malnutrition
Liver disease or kidney dysfunction
Heart attack (especially a large or massive one)
Hyperthyroidism (overactive thyroid)
Uncontrolled diabetes
Sepsis (a severe body-wide infection)
The meaning of low bicarbonate levels can vary based on your blood pH:
When both bicarbonate and blood pH are low (pH < 7.4), the condition is known as metabolic acidosis. It occurs when your body produces too much acid or the kidneys fail to remove enough acid. Common causes include:
Chronic kidney failure
Liver failure
Severe or prolonged diarrhea
Lactic acidosis (from intense exercise, shock, or certain diseases)
Diabetic ketoacidosis
Seizures
Cancer
Prolonged lack of oxygen (hypoxia)
When bicarbonate is low but blood pH is elevated (pH > 7.4), it may indicate respiratory alkalosis, which is often due to excessive loss of CO2 through rapid breathing. Common triggers include:
Hyperventilation
Fever
Severe pain
Anxiety or panic attacks
Certain medications are known to reduce blood bicarbonate levels, either directly or as a side effect of how they affect acid-base regulation:
Methicillin (antibiotic)
Nitrofurantoin (used for urinary tract infections)
Tetracycline (broad-spectrum antibiotic)
Thiazide diuretics (used to manage blood pressure or fluid retention)
Triamterene (a potassium-sparing diuretic)
If your CO2 or bicarbonate levels are low, your doctor will evaluate them alongside other tests such as electrolyte panels, blood pH, and clinical symptoms to determine the root cause and appropriate treatment.
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Unlimited Plan Member since 2021
I have been using Healthmatters.io since 2021. I travel all over the world and use different doctors and health facilities. This site has allowed me to consolidate all my various test results over 14 years in one place. And every doctor that I show this to has been impressed. Because with any health professional I talk to, I can pull up historical results in seconds. It is invaluable. Even going back to the same doctor, they usually do not have the historical results from their facility in a graph format. That has been very helpful.
Karin
Advanced Plan Member since 2020
What fantastic service and great, easy-to-follow layouts! I love your website; it makes it so helpful to see patterns in my health data. It's truly a pleasure to use. I only wish the NHS was as organized and quick as Healthmatters.io. You've set a new standard for health tracking!
Paul
Healthmatters Pro Member since 2024
As a PRO member and medical practitioner, Healthmatters.io has been an invaluable tool for tracking my clients' data. The layout is intuitive, making it easy to monitor trends and spot patterns over time. The ability to customize reports and charts helps me present information clearly to my clients, improving communication and outcomes. It's streamlined my workflow, saving me time and providing insights at a glance. Highly recommended for any practitioner looking for a comprehensive and user-friendly solution to track patient labs!
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