A patient seated in the chair before a blood draw
In person

Carbon Dioxide (CO2)

Your blood’s main acid-base buffer, measured from one blood draw.

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  • 2,000+ lab locations. Find one near you
  • Nothing due at the lab. FSA / HSA accepted
  • Ordered by a licensed clinician

At a glance

Collection
Blood draw
A standard blood draw at the lab.
Preparation
None
Nothing to do ahead of time. Water is fine.
Results
1 to 2 days
Typical turnaround after your visit.
Where
2,000+ lab locations
Nationwide, with nothing due at the lab.

About this test

This test measures carbon dioxide in your blood, mostly in the form of bicarbonate. Bicarbonate helps keep your blood from becoming too acidic or too alkaline, and your kidneys and lungs both help control it. It is usually read with sodium, potassium, and chloride. No fasting is needed.

For adults 18 and older. Test availability varies by lab location.

Who should take this test?

This test is for adults whose healthcare provider wants to follow acid-base balance, often during medication check-ins, kidney follow-up, or after a past electrolyte result.

Ask about this test

Not sure this is the right test?

AI-generated. For information only, not medical advice. Call 911 for an emergency.

What does this test measure?

Your result shows your bicarbonate level, which can help a healthcare provider understand your acid-base balance alongside your other electrolytes and kidney markers.

Carbon dioxide (CO2, bicarbonate)
This result mostly reflects bicarbonate, a form of carbon dioxide that helps keep your blood from becoming too acidic or too alkaline. Your lungs and kidneys work together to hold it steady. It is read with the other electrolytes to look at your body’s acid-base balance.
Why it’s measured: A window on acid-base balance, read with the other electrolytes.

How it works

  1. Step 1

    Order online

    Check out here. A licensed clinician in your state reviews your order and sends it to the lab.

  2. Step 2

    Visit a lab

    Bring a photo ID to any of 2,000+ lab locations. No fasting needed, and nothing is due at the lab.

  3. Step 3

    Get your results

    Results post to your account, usually in 1 to 2 days, each number next to the lab’s reference range.

Find a lab near you

Choose from 2,000+ lab locations nationwide. Your order works at any of them.

What your results tell you

CO2 is reported in millimoles per liter (mmol/L) and compared with the lab’s reference range, which is shown on your report.

  • Your number next to the lab’s reference range
  • Explained in plain language
  • A licensed clinician reviews your order and, if appropriate, orders the test.
  • A lab report you can download and share

Acid-base changes have many possible causes, so talk with a healthcare provider about your result along with your other electrolytes.

Clinical-grade testing, from the comfort of home.

From the lab to your report, every step of our process meets the gold standard in medical testing.

  • CLIA-certified labs

    Every lab we partner with is certified under the Clinical Laboratory Improvement Amendments, meeting both state and federal standards with regular independent inspections.

  • We protect your health data

    We protect your health data with encryption and do not sell it. Some results must be reported to public health authorities by law. See our Privacy Notice.

  • Rigorous quality assurance

    All partner labs run regular internal quality checks, participate in proficiency testing, and comply with federal and state lab regulations.

  • Clinician-reviewed reports

    Results are reviewed by an independent, licensed clinician.

Questions

Common questions.

Anything else, our care team answers by phone, text, or email.

They are related. Your cells make carbon dioxide as they use energy, and much of it travels in the blood as bicarbonate before your lungs breathe it out. This test measures that total, which mostly reflects bicarbonate, a buffer that helps hold acid-⁠base balance steady.

CO2 is read together with sodium, potassium, and chloride because they shift in related ways. A healthcare provider looks at the pattern, not one number, when thinking about hydration, kidney function, breathing, or medicines that affect acid-⁠base balance.

A single CO2 result does not explain why a value is high or low, and it does not measure how well your lungs work. It is one part of an acid-⁠base picture that a healthcare provider puts together with your other results, symptoms, and history.

Lab tests are informational and don’t diagnose conditions on their own. Available to adults 18 and older; test availability varies by lab location. A licensed clinician reviews your order and, if appropriate, orders the test. All testing is performed at CLIA-certified laboratories. Not for emergencies: if you think you may be having a medical emergency, call 911.