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Carbon Monoxide in Exhaled Breath (Fraction)

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

This test measures the amount of carbon monoxide (CO) present in the air you exhale, often used to assess lung function and exposure to smoke or pollutants.

Quick summary

["Helps track lung health and exposure risks from environmental factors."]

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

Key facts at a glance

LOINC
29362-1
Short code
Deprecated S pneumB Ag Ser Ql
Synonyms
Deprecated S pneumB Ag Ser Ql
Category
coagulation
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
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 This Test Is Done

Your healthcare provider may order this test if you have symptoms like shortness of breath, cough, or if you’ve been exposed to smoke, fumes, or other substances that could affect your lungs. It can also be used in research or occupational settings to monitor air quality or exposure to harmful gases.

How the Test Works

You’ll breathe into a special device that captures your exhaled breath. The device measures the concentration of carbon monoxide, which binds to hemoglobin in your blood. This test is quick, painless, and doesn’t require blood or other bodily fluids.

What to Expect Before the Test

No special preparation is needed. You may want to avoid smoking or using mouthwash with alcohol-based products before testing, as these can interfere with results.

What the Results Mean

Higher than normal levels may indicate recent exposure to smoke, fumes, or other pollutants. Very high levels could suggest severe lung damage or poisoning. Your provider will discuss results in the context of your health history and symptoms.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

CO in Breath

Frequently asked questions

What does elevated carbon monoxide levels indicate?
Elevated levels may suggest recent exposure to smoke, carbon monoxide poisoning, or lung disease. It’s important to discuss these findings with your healthcare provider to determine the next steps, such as further testing or changes to your environment.
How long does it take to get results?
Results are typically available immediately after the test, as it’s a quick, non-invasive procedure. However, your healthcare provider will review the results and discuss them with you.
Can I smoke or drink before this test?
Avoid smoking or using mouthwash with alcohol-based products for at least 30 minutes before testing, as these can affect the accuracy of the 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