Carbon Monoxide (CO)
A carbon monoxide blood test is used to detect
poisoning from breathing carbon monoxide (CO), a
colorless, odorless, poisonous gas. The test measures the amount of hemoglobin
that has bonded with carbon monoxide. This amount is also called the
carboxyhemoglobin level. See a picture of
what happens during carbon monoxide poisoning .
When a person inhales carbon monoxide,
it combines with the red blood cells that normally carry oxygen to the body's
tissues and replaces the oxygen that is normally carried in the blood. As a
result, less oxygen is carried to the brain and other body tissues. Carbon
monoxide can cause severe poisoning and death.
Carbon monoxide is
made during burning when there is not enough oxygen present for complete
combustion. The main sources of carbon monoxide are engine fumes (such as from cars or boats),
fires burning with poor ventilation (such as gas heaters and indoor cooking
fires), factories, and smoking tobacco.
Why It Is Done
A carbon monoxide blood test is used to
detect poisoning from breathing carbon monoxide. You might have this test if
you have been exposed to the gas or if you have unexplained symptoms, such
How To Prepare
Do not smoke before you have this
Talk to your doctor about any concerns you have regarding
the need for the test, its risks, how it will be done, or what the results may
mean. To help you understand the importance of this test, fill out the
medical test information form(What is a PDF document?).
How It Is Done
The health professional drawing blood
- Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.
- Clean the needle site with
- Put the needle into the vein. More than one needle stick
may be needed.
- Attach a tube to the needle to fill it with
- Remove the band from your arm when enough blood is
- Put a gauze pad or cotton ball over the needle site as
the needle is removed.
- Put pressure on the site and then put on a
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
There is very little chance of a
problem from having 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
- In rare cases, the vein may become swollen after the blood
sample is taken. This problem is called phlebitis. A warm compress can be used
several times a day to treat this.
- Ongoing bleeding can be a
problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and
other blood-thinning medicines can make bleeding more likely. If you have
bleeding or clotting problems, or if you take blood-thinning medicine, tell
your doctor before your blood sample is taken.