The Silent Killer: Carbon Monoxide

Centers for Disease Control and Prevention National Center for Environmental Health Division of Environment Hazards and Health Effects Air Pollution and Respiratory Health Branch


February 08, 2013

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In This Article

Evaluation of Patients With Possible CO Poisoning

Add these 7 considerations to your patient intake dialogue to prevent missing a diagnosis of CO poisoning:

1. Diagnosis is based on a suggestive history and physical findings coupled with confirmatory testing. If CO poisoning is suspected, patients should be examined for conditions that include smoke inhalation, trauma, medical illness, or intoxication.

2. Neurologic exam should include an assessment of cognitive function such as a Mini-Mental Status Exam.

3. The key to confirming the diagnosis is measuring the patient's carboxyhemoglobin (COHb) level. It is important to determine how much time has elapsed since the patient has left the toxic environment, because that will influence the COHb level. If the patient has been breathing room air normally for several hours, COHb testing may be less useful. The following are key points in measuring COHb:

   • An elevated COHb level of 2% for nonsmokers and > 9% for smokers strongly supports a diagnosis of CO poisoning.

   • Carbon monoxide levels can be tested either in whole blood or exhaled air.

4. The most common technology available in hospital laboratories for analyzing the blood is the multiple wavelength spectrophotometer, also known as a CO-oximeter. Venous or arterial blood may be used for testing.

5. A fingertip pulse CO-oximeter can be used to measure heart rate, oxygen saturation, and COHb levels. The conventional 2-wavelength pulse oximeter is not accurate when COHb is present.

6. COHb levels do not correlate well with the severity of illness, outcomes, or response to therapy, so it is important to assess clinical symptoms and history of exposure when determining the type and intensity of treatment.

7. Carbon monoxide can be produced endogenously as a byproduct of heme metabolism. Patients with sickle cell disease can have an elevated COHb level as a result of hemolytic anemia or hemolysis

Other testing such as a fingerstick blood sugar, alcohol and toxicology screen, head CT scan, or lumbar puncture may be needed to exclude other causes of altered mental status when the diagnosis of carbon monoxide poisoning is inconclusive.