Carbon Monoxide (Blood)
Does this test have other names?
CO blood test, CO blood gas, arterial blood gas
What is this test?
This test measures the level of carbon monoxide (CO) in your blood.
Carbon monoxide is a colorless, tasteless, and odorless gas made by combustion. Breathing
in CO can be fatal because it doesn't allow oxygen to get to your heart and other
This test looks for carboxyhemoglobin. This substance is made in your blood when hemoglobin
combines with carbon monoxide instead of oxygen.
Most deaths from CO result from smoke inhalation. Other sources include heaters that
don’t work as they should, kitchen stoves and tools that are not vented correctly,
camping stoves, charcoal grills, water heaters, and cars with their engines running
in an enclosed space like a garage. All of these can cause CO to spread throughout
Why do I need this test?
You may need this test if your healthcare provider thinks you have CO poisoning. Symptoms
of carbon monoxide poisoning include:
Severe poisoning can cause nerve system symptoms such as:
Carbon monoxide poisoning can be hard to recognize in very young children. For example,
a child may merely appear fussy and not want to eat.
You may also have this test if you have been in contact with CO. This is especially
true if you inhaled smoke during a fire. You may also have this test if you've been
near a car that had its engine running in an enclosed space for a long time.
What other tests might I have along with this test?
Your healthcare provider may also order these tests:
Your provider may also order an MRI scan if you also have symptoms of nervous system
What do my test results mean?
Many things may affect your lab test results. These include the method each lab uses
to do the test. Even if your test results are different from the normal value, you
may not have a problem. To learn what the results mean for you, talk with your healthcare
Results are given as a percentage or as a decimal. These are the normal ranges for
CO levels in the blood:
Adults: less than 2.3%, or 0.023
Adult smokers: 2.1% to 4.2%, or 0.021 to 0.042
Adult heavy smokers (more than 2 packs a day): 8% to 9%
Hemolytic anemia: Up to 4%
Newborn: greater than 12%
If your levels are higher, you may have CO intoxication or poisoning.
How is this test done?
The test requires a blood sample, which is drawn through a needle from a vein in your
Does this test pose any risks?
Taking a blood sample with a needle carries risks that include bleeding, infection,
bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight
stinging sensation or pain. Afterward, the site may be slightly sore.
What might affect my test results?
Other factors aren't likely to affect your results.
How do I get ready for this test?
You don't need to prepare for this test. But be sure your healthcare provider knows
about all medicines, herbs, vitamins, and supplements you are taking. This includes
medicines that don't need a prescription and any illicit drugs you may use.