Carbon Monoxide (CO)

Carboxyhemoglobin

Results

A carbon monoxide blood test is used to detect poisoning from breathing carbon monoxide (CO), a colorless, odorless, poisonous gas. The test measures the level of a compound called carboxyhemoglobin.

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 poisoning.

Results are usually available right away.

Normal

Carbon monoxide

Nonsmokers:	Less than 3% of total hemoglobin
Smokers:	2%–10% of total hemoglobin

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.

Symptoms related to high carbon monoxide values

Percent of total hemoglobin	Symptoms
20%–30%	Headache, nausea, vomiting, and trouble making decisions
30%–40%	Dizziness, muscle weakness, vision problems, confusion, and increased heart rate and breathing rate
50%–60%	Loss of consciousness
Over 60%	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.

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Author:	Maria G. Essig, MS, ELS	Last Updated: March 18, 2008
Medical Review:	Caroline S. Rhoads, MD - Internal Medicine R. Steven Tharratt, MD, MPVM, FACP, FCCP - Pulmonology, Critical Care, Medical Toxicology
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