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Total Carbon Dioxide (Plasma/Serum) by Acid-Base Chemistry

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

This test measures the amount of carbon dioxide 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 are critical for maintaining healthy pH and respiratory function."]

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

Key facts at a glance

LOINC
62264-7
Short code
CO2 VFr/PPres Gas DS
Synonyms
CO2 VFr/PPres Gas DS
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 carbon dioxide (TCO₂) includes both dissolved CO₂ and bicarbonate ions (HCO₃⁻) in your blood plasma or serum. This test reflects your body’s buffering capacity against acidity, influenced by respiration and metabolic processes.

Why Is This Test Done?

Doctors may order this test to evaluate conditions like respiratory disorders (e.g., COPD), metabolic acidosis/alkalosis, kidney function, or fluid balance issues. It’s often paired with other blood gas tests (e.g., pH, oxygen levels).

How Is the Test Performed?

A small blood sample is drawn from a vein (usually in your arm). The sample is sent to a lab where specialized equipment measures CO₂ content using acid-base chemistry methods, such as blood gas analyzers.

What Do Results Mean?

Results help determine whether your body is producing too much or too little CO₂, which can indicate problems with breathing, kidney function, or metabolic processes. Abnormal levels may signal underlying health concerns requiring further evaluation.

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.

◆Associated findings1

Short name

Total CO₂

Frequently asked questions

How does carbon dioxide relate to acid-base balance in my body?
Carbon dioxide acts as a key regulator of blood pH. When you exhale, your lungs remove excess CO₂, helping maintain a balanced pH. High levels may signal hypercapnia (too much CO₂), while low levels may suggest hypocarbia (too little), often linked to respiratory or metabolic disorders.
Can diet or exercise affect my CO₂ test results?
Yes, diet (e.g., high-protein or low-carb meals) and physical activity can temporarily alter CO₂ levels, especially if they impact breathing or metabolism. However, results are typically interpreted in the context of your overall health and symptoms, not just diet alone.
What symptoms might indicate abnormal CO₂ levels?
Symptoms like shortness of breath, fatigue, confusion, or rapid breathing may signal abnormal CO₂ levels. Always discuss symptoms with your healthcare provider, as they may relate to conditions like asthma, heart disease, or kidney problems.
  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