Skip to content

Total Carbon Dioxide in Blood (Arterial or Venous)

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 acidity and alkalinity (acid-base balance).

Quick summary

["Your blood’s CO₂ levels help doctors check for conditions like respiratory issues or metabolic disorders."]

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

Key facts at a glance

LOINC
34520-7
Short code
CO2 BldCo-sCnc
Synonyms
CO2 BldCo-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
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

Why It’s Done

Doctors may order this test if you have symptoms like shortness of breath, fatigue, or signs of acid-base imbalances. It’s also used in monitoring conditions like chronic obstructive pulmonary disease (COPD) or kidney problems.

What to Expect

A blood sample is taken from a vein (usually in your arm), and the CO₂ content is measured. The test is quick and typically done in a lab.

Normal vs. Abnormal Results

While exact ranges vary by lab, abnormal results may signal respiratory or metabolic issues. Your doctor will interpret the results in the context of your symptoms and overall health.

Common Conditions It Helps Diagnose

This test can help diagnose or monitor respiratory disorders (e.g., pneumonia, asthma), metabolic acidosis or alkalosis, or kidney function. It’s also useful in assessing patients with chronic illnesses like diabetes or heart 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.

CO₂ levels reflect how efficiently your lungs remove carbon dioxide and how your body compensates for acid-base imbalances. Low levels may indicate hyperventilation or respiratory alkalosis, while high levels could suggest hypoventilation or metabolic acidosis.

Short name

CO₂ Blood

Frequently asked questions

What does a high or low CO₂ level mean?
A high CO₂ level (hypercapnia) may mean your lungs aren’t working well, or your body isn’t removing enough carbon dioxide. A low level (hypocapnia) could suggest you’re breathing too quickly, which might happen with anxiety or certain medications.
Does this test require fasting?
No fasting is usually required for this test, but your doctor may ask you to avoid certain medications or foods that could affect results (like caffeine or alcohol). Always follow your provider’s instructions.
Can I take this test at home?
No, this test requires a blood sample collected by a healthcare professional in a clinical setting. Some at-home blood pressure monitors may measure related metrics, but CO₂ levels are only tested in labs.
  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