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Carbon Dioxide (Total) in Plasma/Serum

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

This test measures the amount of carbon dioxide dissolved in your blood plasma or serum, which helps assess how well your body is balancing acidity and alkalinity.

Quick summary

["Total CO₂ levels help doctors check if your blood pH is stable and identify potential acid-base imbalances."]

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

Key facts at a glance

LOINC
39464-3
Short code
CO2 DiafP-sCnc
Synonyms
CO2 DiafP-sCnc
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
SNOMED
394971007
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

Why Is This Test Done?

Your healthcare provider may order this test to evaluate conditions affecting your body’s acid-base balance, such as respiratory or metabolic disorders. It’s often used alongside other blood tests like pH or bicarbonate levels to diagnose issues like respiratory failure, kidney disease, or diabetic ketoacidosis.

What to Expect Before the Test

No special preparation is needed for this test. You may have a small needle inserted into your arm or vein to draw blood. If done via a fingerstick, it’s quick and painless. If you’re on blood thinners, let your provider know to avoid excessive bruising.

What the Results Mean

Total CO₂ levels can indicate whether your body is producing too much or too little carbon dioxide. Low levels may suggest hyperventilation or overcompensation from metabolic issues, while high levels could point to conditions like respiratory depression or kidney problems.

Common Conditions Monitored

This test is commonly used to monitor patients with chronic obstructive pulmonary disease (COPD), kidney disease, or those with severe infections. It also helps track responses to treatments like diuretics or mechanical ventilation.

Reference range

Adult: 22-28 mmol/LN/A

Specimen: serum

No special preparation required. For PSA, avoid sexual activity for 24-48 hours before the test.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Total CO₂ (Plasma/Serum)

Frequently asked questions

What does a low total CO₂ level mean?
A low total CO₂ level may suggest your body is losing too much carbon dioxide (e.g., from rapid breathing or overuse of diuretics) or that your kidneys are not processing it properly. This could indicate conditions like hyperventilation, metabolic alkalosis, or certain kidney disorders.
What does a high total CO₂ level mean?
A high total CO₂ level may indicate your body is retaining too much carbon dioxide, which can happen with respiratory issues (e.g., hypoventilation) or kidney problems that fail to excrete waste products properly. It may also appear in severe dehydration or certain metabolic disorders.
Can diet affect total CO₂ levels?
Dietary factors like high protein intake or certain medications (e.g., diuretics) can indirectly influence blood chemistry, including CO₂ levels. However, total CO₂ is primarily measured in blood, so dietary changes alone won’t directly alter this test result unless they affect hydration, breathing, or kidney function.
  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