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First Aid & Emergencies

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Carbon Monoxide (CO)

How It Feels

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.


There is very little chance of a problem from having a blood sample taken from a vein.

  • You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
  • In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. You can treat this by using a warm compress several times a day.

Bleeding can be a problem for people who have bleeding disorders or take blood-thinning medicines such as aspirin or warfarin (Coumadin). If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.


A carbon monoxide blood test is used to detect carbon monoxide poisoning. Poisoning can happen if you breathe air that contains too much carbon monoxide. The test measures the amount of hemoglobin that has bonded with carbon monoxide. This is called the carboxyhemoglobin level.

The results are reported as a percentage. They show the amount of carbon monoxide bound to hemoglobin divided by the total amount of hemoglobin (multiplied by 100). The higher the percentage, the greater the risk of having symptoms of carbon monoxide poisoning camera.gif. A person with values below 10% may not have any symptoms.

These numbers are just a guide. The range for "normal" varies from lab to lab. Your lab may have a different range. Your lab report should show what range your lab uses for "normal." Also, your doctor will evaluate your results based on your health and other factors. So a number that is outside the normal range here may still be normal for you.

Results are usually available right away.


Carbon monoxide 1

People who don't smoke:

Less than 2% of total hemoglobin

People who smoke:

4%-8% of total hemoglobin

High values

WebMD Medical Reference from Healthwise

Last Updated: August 07, 2014
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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