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Total Carbon Dioxide in Blood (Calculated from Arterial Blood Gas)

Published: August 9, 2026Updated: August 16, 2026

This test measures the amount of carbon dioxide dissolved in your blood, calculated from an arterial blood gas (ABG) sample. It helps assess how well your body is balancing acidity and alkalinity in your bloodstream.

Quick summary

["Helps diagnose and monitor conditions affecting blood acid-base balance."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
41647-9
Short code
CO2 BldA Calc-sCnc
Synonyms
CO2 BldA Calc-sCnc
Category
chemistry
Sample
whole-blood
Container
Lavender-top (EDTA)
Units
N/A
Ref low
22
Ref high
28
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
calculated
CPT
82374
Specimen volume
3 mL
Stability
Room temperature: 4h, Refrigerated: 24h
Hemolysis max
0
Lipemia max
0
Icterus max
0
TAT
4–24 hours
Order
routine

What Does This Test Measure?

Total carbon dioxide (CO₂) is a key component of your blood’s acid-base balance. It’s derived from the arterial blood gas test, which measures oxygen, carbon dioxide, and pH levels. This test specifically quantifies the dissolved CO₂ in your blood, which can indicate how efficiently your lungs are removing waste gases and maintaining proper acidity levels.

Why Might You Need This Test?

Your doctor may order this test if you have symptoms like shortness of breath, rapid breathing, or signs of respiratory or metabolic disorders. It’s also used in monitoring patients with chronic lung diseases, kidney issues, or those receiving treatments affecting acid-base balance.

When Is This Test Performed?

This test is typically performed on an arterial blood sample, often taken from a radial artery in your wrist. It’s usually done quickly in a clinical setting, especially if you’re experiencing respiratory distress or undergoing intensive medical care.

What Are Common Conditions Monitored With This Test?

Total CO₂ levels help identify conditions like respiratory acidosis (too much CO₂), respiratory alkalosis (too little CO₂), metabolic acidosis or alkalosis, and kidney-related imbalances. It’s also useful in assessing patients with conditions like chronic obstructive pulmonary disease (COPD), asthma, or kidney failure.

Reference range

Adult: 22-28 mmol/LN/A

Specimen: whole-blood

No special preparation usually required. Stay well hydrated. Inform your healthcare provider of all medications and supplements you are taking.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

Total CO₂ levels provide critical insights into your body’s ability to regulate acid-base balance. Abnormal results can signal underlying issues such as inefficient lung function, fluid imbalances, or metabolic disorders. Doctors use these findings to adjust treatments, such as oxygen therapy, medication, or lifestyle changes, to restore balance and improve health outcomes.

Short name

CO₂ in arterial blood (calculated)

Frequently asked questions

What does a high or low total CO₂ level mean?
A high total CO₂ level may suggest respiratory acidosis, where your body retains too much CO₂ (common in conditions like severe asthma or COPD). A low level could indicate respiratory alkalosis, often seen in hyperventilation or high-altitude exposure. Your doctor will interpret results in the context of your symptoms and overall health.
Unlike standard blood tests that measure individual components like glucose or cholesterol, this test specifically calculates CO₂ levels from an arterial blood sample. It’s part of an arterial blood gas (ABG) panel, which also includes measurements of oxygen saturation, pH, and bicarbonate levels to assess acid-base balance comprehensively.
Yes, drawing blood from an artery can be slightly more uncomfortable than a standard vein draw, but it’s usually done quickly. You may feel a brief pinch or pressure, and some patients experience mild bruising afterward. Your healthcare provider will explain the process and ensure you’re comfortable.
While lifestyle factors like diet, exercise, or smoking may indirectly influence your overall health, they don’t directly alter the calculated CO₂ levels in this test. However, conditions like chronic lung disease or kidney problems that affect acid-base balance could be influenced by lifestyle choices.
The frequency depends on your health condition. If you have a chronic illness like COPD or kidney disease, your doctor may recommend regular monitoring. Otherwise, this test is typically ordered only when symptoms or medical needs warrant it, such as during acute illness or before certain treatments.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy