carbon monoxide (co) test

test overview

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 (co). this gas has no colour, odour, or taste, so you can't tell when you are breathing it. the test measures the amount of hemoglobin in your blood that has bonded with carbon monoxide.

carbon monoxide can come from any source that burns fuel. common sources are cars, fireplaces, powerboats, woodstoves, kerosene space heaters, charcoal grills, and gas appliances such as water heaters and ovens. these things usually cause no problems. but if they are not used or installed properly, carbon monoxide may build up in an enclosed space.

when you inhale carbon monoxide, it replaces the oxygen that is normally carried by the hemoglobin in your red blood cells. as a result, your brain and other tissues get less oxygen. this can cause serious symptoms or death.

why it is done

this test may be done if you have been exposed to carbon monoxide or if you have unexplained symptoms, such as:

• headache, dizziness, or vision problems.
• nausea or vomiting.
• muscle weakness.
• confusion or trouble thinking.
• extreme sleepiness.

how to prepare

do not smoke before you have this test. tobacco smoke contains carbon monoxide.

how it is done

a health professional uses a needle to take a blood sample, usually from the arm.

watch

how it feels

when a blood sample is taken, you may feel nothing at all from the needle. or you might feel a quick sting or pinch.

risks

there is very little chance of having a problem from this test. when a blood sample is taken, a small bruise may form at the site.

results

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). this is called the carboxyhemoglobin level.

results are usually available right away.

normal

each lab has a different range for what's normal. your lab report should show the range that your lab uses for each test. the normal range is just a guide. your doctor will also look at your results based on your age, health, and other factors. a value that isn't in the normal range may still be normal for you.

high values

high blood carbon monoxide values are caused by carbon monoxide poisoning. symptoms of carbon monoxide poisoning become more severe as the carbon monoxide levels increase.

women and children usually have fewer red blood cells than men do. so women and children may have more severe symptoms at lower levels.