EBSCO Health

Print PageSend to a Friend
Health Library Home>Article


Pronounced: car-BOXY-heem-uh-glow-ben

What Is Carboxyhemoglobin?

Carboxyhemoglobin is formed when carbon monoxide gas binds with hemoglobin in the blood.

Hemoglobin is a protein that carries oxygen in red blood cells. It can permanently bind to hemoglobin when carbon monoxide gas is inhaled. This replaces the oxygen that hemoglobin normally carries and slows down oxygen delivery to organs.

Reason for the Test

This test is done when carbon monoxide poisoning is suspected.

This test can also be used to monitor the treatment and recovery of people who have been diagnosed with carbon monoxide poisoning.

Type of Sample Taken

A blood sample will be taken from a vein in the arm.

Prior to Collecting the Sample

You do not need to do anything special before this test.

During the Sample Collection

You will be asked to sit. An area inside your elbow will be cleaned with a wipe. A large band will be tied around your arm. The needle will be put in a vein. A tube will collect the blood from the needle. The band on your arm will be taken off. After the blood is collected, the needle will be removed. Gauze will be held on the site to help stop bleeding. You may also be given a bandage. This test takes about 5-10 minutes.

After Collecting the Sample

After the blood sample is taken, you may need to stay seated for 10 to 15 minutes. If you are lightheaded, you may need to stay seated longer. When you feel better, you can leave.

A bit of blood may ooze from the vein beneath the skin. It will cause a bruise. A bruise will usually fade in a day or two.

Call your doctor right away if you have redness, swelling, lasting bleeding, or pain.


You will get your results as soon as possible.

In smokers, levels of carboxyhemoglobin range from 2.1% to 10%. In nonsmokers, normal levels are less than 2.3%.

Talk to your doctor about your test results. A test may point to an illness that you do not have. It can also miss an illness that you may have. The doctor will check your symptoms and all test results before making a diagnosis.


Blood gases. Lab Tests Online—American Association for Clinical Chemistry website. Available at: http://labtestsonline.org/understanding/analytes/blood-gases/tab/faq. Updated May 1, 2019. Accessed May 13, 2019.

Carbon monoxide poisoning. Centers for Disease Control and Prevention website. Available at: http://www.cdc.gov/co/. Updated September 16, 2018. Accessed May 13, 2019.

Carbon monoxide toxicity. EBSCO DynaMed website. Available at:http://www.dynamed.com/topics/dmp~AN~T115658/Carbon-monoxide-toxicity. Updated May 2, 2019. Accessed May 13, 2019.

Carboxyhemoglobin measurement. EBSCO DynaMed website. Available at:http://www.dynamed.com/topics/dmp~AN~T906782/Carboxyhemoglobin-measurement.Updated October 8, 2018. Accessed May 13, 2019.

Last reviewed March 2019 by EBSCO Medical Review Board James P. Cornell, MD  Last Updated: 5/13/2019