Doctors can check people’s blood for typical or atypical carbon dioxide (CO2) levels to help diagnose certain medical conditions. For example, a carbon dioxide test or CO2 test can help diagnose kidney and respiratory problems.
The CO2 test is a simple blood test that measures the amount of CO2 gas in a person’s blood. It is usually part of a larger test known as an electrolyte panel. Healthcare professionals may refer to this as a basic metabolic panel.
The kidneys and lungs maintain the concentration of CO2 in the blood. If a person’s blood CO2 levels are above the typical range, a doctor may request further tests to check kidney and lung function to assess other gasses in the blood or check for fluid retention.
In this article, we look at the CO2 test, typical blood CO2 levels, and what atypical results might mean.
The CO2 blood test measures the amount of carbon dioxide in the blood. Carbon dioxide can be present in the form of CO2, bicarbonate (HCO3), and carbonic acid (H2CO3). It mainly occurs in the form of bicarbonate.
As part of its typical functions, the human body naturally produces certain acids and bases that balance each other. Any disruption to this balance can be an early sign of an underlying medical condition.
Carbon dioxide is an acidic component because it
A healthcare professional can measure the levels of CO2 in a person’s blood using a simple blood test. They may take blood from either an artery, which involves an arterial blood draw, or a vein, which involves a venous blood draw.
A venous blood draw provides a measure of bicarbonate levels. An arterial blood draw
A
The test procedure usually takes around 2 to 5 minutes. A nurse or healthcare professional will make a tiny prick in the person’s arm and collect blood in a test tube to send away for testing.
A person may experience a slight feeling of discomfort from where the nurse drew the blood, but this is temporary and will resolve on its own.
A healthcare professional may order a CO2 test as part of a routine checkup or to investigate the underlying cause of certain symptoms. They may also recommend it in the case of a medical emergency or just before surgery.
People experiencing the following symptoms may receive a CO2 blood test:
A healthcare professional will likely perform a CO2 blood test as part of an electrolyte panel to check a person’s bicarbonate levels.
This test measures levels of electrolytes, including sodium, chloride, and potassium, in the blood, along with bicarbonate levels. Electrolytes keep the body’s fluid balance in check and help maintain heart rhythm, muscle contractions, and brain function.
The electrolyte panel tells doctors how well a person’s kidneys are functioning. High or low bicarbonate levels can indicate that a person has metabolic alkalosis or acidosis, respectively.
Both arterial and venous blood draws can provide an overall picture of a person’s electrolyte status and the balance of acids and bases in their blood.
Results of the CO2 test may vary depending on the person’s age, sex, and medical history, as well as the test administration method and whether the individual takes any type of medication.
In most cases, reference ranges vary depending on the laboratory conducting the test, due to differing types of equipment and testing methods. The type of units that healthcare professionals use to report results can also vary between laboratories.
LabTestsOnlineUK notes that the typical range of total blood CO2 (bicarbonate) is 22 to 29 millimoles per liter (mmol/L) according to the International System of Units (SI units). This is equivalent to 22 to 29 milliequivalents per liter (mEg/L) for conventional units.
Changes in CO2 levels may suggest that someone is losing or retaining typical body fluids. This points to an imbalance in the body’s electrolyte system.
However, people should note that while an atypical CO2 test result could mean that there are either high or low CO2 levels in the body, they may not always indicate a problem. A person can discuss their results with a doctor.
A person may have low total blood CO2 if their levels are lower than 22 mmol/L or 22 mEg/L. However, these ranges can vary between laboratories.
Lower-than-typical CO2 levels could indicate:
- Addison’s disease
- diabetic ketoacidosis, where the body produces too many blood acids
- poisoning with ethylene glycol, such as from antifreeze poisoning
- metabolic acidosis, which can be due to conditions such as kidney disease, liver disease, and persistent diarrhea
- respiratory alkalosis, which results from respiratory disorders such as hyperventilation
- salicylate toxicity, such as from an aspirin overdose
- lactic acidosis, or a buildup of lactate in the body
A person may have high total blood CO2 if their levels are higher than 29 mmol/L or 29 mEg/L. However, these ranges can vary between laboratories.
Higher-than-typical CO2 levels may indicate:
- lung conditions
- Cushing’s syndrome
- hyperaldosteronism, a condition that affects the adrenal glands
- respiratory tract infection
- metabolic alkalosis, which can result from dehydration, vomiting, and anorexia
- kidney failure
As with any simple blood draw, people may experience minor side effects from the CO2 test. The risks are minor and may include:
- bleeding, bruising, or pain at the site of the needle prick
- lightheadedness
- dizziness
- formation of a hematoma, or a lump of blood under the skin’s surface
If these symptoms persist for longer than a day or worsen, a person needs to inform a doctor.
Carbon dioxide (CO2) is a naturally occurring gas in the body. Levels of CO2 may increase or decrease for a number of reasons.
Undergoing a CO2 blood test can help healthcare professionals identify any underlying medical conditions that are present, which a doctor will be able to diagnose and treat.