Carbon Monoxide (CO)
A carbon monoxide blood test is used to
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 is also called the
Carbon monoxide results are reported as
a percentage: The amount of carbon monoxide bound to hemoglobin is divided by
the total amount of hemoglobin (and then multiplied by 100). The higher the
percentage, the greater the risk of having symptoms of carbon monoxide
poisoning. With values below 10%, a person may not have any symptoms of
The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what’s normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Results are usually available right away.
Less than 2% of total hemoglobin
4%–8% of total hemoglobin
carbon monoxide values are caused by carbon monoxide poisoning. Symptoms of
carbon monoxide poisoning become more severe as the carbon monoxide levels
Symptoms related to high carbon monoxide values1
| Percent of total hemoglobin|| Symptoms|
Headache, nausea, vomiting, and trouble
Dizziness, muscle weakness, vision
problems, confusion, and increased heart rate and breathing rate
Loss of consciousness
Seizures, coma, death
Women and children may have more severe symptoms of carbon
monoxide poisoning at lower carbon monoxide levels than men because women and
children usually have fewer red blood cells.
What Affects the Test
- Smokers already have some carbon monoxide in their blood.
who are regularly exposed to car exhaust, such as taxi drivers and traffic
police, often have high carbon monoxide levels (8% to 12%).
What To Think About
- A person with symptoms and possible exposure to carbon monoxide,
such as someone who lives in a house with an old heating system and complains
of ongoing headaches, should be tested for carbon monoxide
- A person who may have carbon monoxide poisoning should
be removed from the place of likely exposure and given oxygen to breathe before
carbon monoxide poisoning is suspected, other tests (such as arterial blood
gases and a complete blood count) may be done. An arterial blood gas (ABG) test
may be done to determine whether symptoms are caused by carbon monoxide
poisoning or by another disease that causes similar symptoms. See the topics
Arterial Blood Gases (ABG) and
Complete Blood Count (CBC).