Skip to content

Total Carbon Dioxide (Total CO₂) in Blood

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

This test measures the amount of carbon dioxide dissolved in your blood, which helps assess how well your body is balancing acids and bases (acid-base balance).

Quick summary

["Your blood’s carbon dioxide levels help determine if your body is maintaining proper pH balance."]

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

Key facts at a glance

LOINC
19889-5
Short code
CO2 VFr ExG
Synonyms
CO2 VFr ExG
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
22
Ref high
28
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
82374
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

What Does This Test Measure?

Total CO₂ in your blood includes both dissolved carbon dioxide and bicarbonate ions, which are critical for buffering acidity. This test reflects your body’s ability to regulate these compounds, often in relation to respiratory or metabolic processes.

Why Might You Need This Test?

Doctors may order this test to evaluate conditions affecting acid-base balance, such as respiratory disorders (e.g., chronic obstructive pulmonary disease), metabolic disorders (e.g., kidney disease), or to monitor treatment responses in patients with conditions like diabetes or heart failure.

How Is This Test Performed?

A small blood sample is drawn from a vein, typically in your arm. The sample is analyzed in a lab to measure the total carbon dioxide content, often using methods like blood gas analysis or automated chemistry analyzers.

What Are Common Uses?

This test is commonly used alongside other blood gas tests (like pH and bicarbonate) to diagnose and monitor conditions that disrupt normal acid-base equilibrium, such as respiratory acidosis or alkalosis.

Reference range

Adult: 22-28 mmol/LN/A

Specimen: serum

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.

Abnormal total CO₂ levels can indicate underlying issues like poor lung function (reducing CO₂ removal), kidney problems (affecting bicarbonate production), or metabolic imbalances. High levels may suggest respiratory alkalosis, while low levels could signal respiratory acidosis or other metabolic disturbances.

Short name

Total CO₂

Frequently asked questions

What does a high or low total CO₂ level mean?
A high total CO₂ level may suggest respiratory alkalosis (e.g., due to rapid breathing or overventilation) or conditions that reduce CO₂ elimination by the lungs. A low level could indicate respiratory acidosis (e.g., due to hypoventilation) or metabolic factors like kidney disease.
How often should I get this test?
The frequency depends on your health condition. Your healthcare provider will determine if regular monitoring is needed, such as for chronic lung diseases, kidney problems, or other conditions affecting acid-base balance.
Can diet or lifestyle affect this test results?
Dietary changes (e.g., high-protein or high-fat meals) or physical activity can temporarily influence blood gas levels, including CO₂. Avoid heavy meals or strenuous exercise before testing to ensure accurate results.
  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