Carbon Monoxide, Whole Blood

Whole blood

7 mL

0.6 mL

Lavender-top (EDTA) tube or green-top (heparin) tube; submit original full, unopened tube.

A morning specimen is not as good as one that is drawn in the late afternoon or evening, especially if the patient is an outpatient who may have occupational exposure (ie, policemen, firemen on day shifts, mechanics). CO tends to be cleared from the blood in hours. Treatment for carbon monoxide poisoning involves removal of the individual from the contaminated area and the administration of oxygen. The half-life of carboxyhemoglobin is five to six hours when the patient breathes room air; it is reduced to 1 to 1¹/₂ hours when the patient breathes 100% oxygen. In severe cases, hyperbaric oxygen treatment at two to three atmospheres is recommended, if available. In the latter instance, the carboxyhemoglobin half-life is reduced to approximately 25 minutes. Hyperbaric oxygen therapy may reduce the incidence of neurological manifestations after exposure. Hyperbaric oxygen therapy has been recommended when the carboxyhemoglobin concentration exceeds 25%. Some have cautioned against basing decisions to institute hyperbaric oxygenation solely on the carboxyhemoglobin concentration owing to the inconsistent correlation between such a measurement and clinical severity.

Determine the extent of carbon monoxide poisoning, toxicity; check on the effect of smoking on the patient; work up headache, irritability, nausea, vomiting, vertigo, dyspnea, collapse, coma, convulsions; work up persons exposed to fires and smoke inhalation

Carbon monoxide levels are of limited value in testing for smoking, since it is cleared rapidly. The half-life of carboxyhemoglobin in individuals with normal cardiopulmonary function is one to two hours. Urinary cotinine, if available, is preferable as a test for tobacco use. Arterial blood gases may be of limited value in treatment decisions for carbon monoxide poisoning.²

Co-oximetry

• Environmental exposure: Nonsmoker: <2.0%, smoker: <9.0%

• Occupational exposure: BEI®: 3.5%¹

Carboxyhemoglobin is useful in judging the extent of carbon monoxide toxicity and in considering the effect of smoking on the patient. A direct correlation has been claimed between CO level and symptoms of atherosclerotic diseases, intermittent claudication, angina, and myocardial infarction. Exposure may occur not only from smoking but also from garage exposure, and from various motors. This test may be included when blood gases are ordered, when there is sufficient sample, and when such instrumentation is available.

A danger of missed diagnosis of CO intoxication is continued exposure of the patient and others to a toxic environment.³ The cherry red color of CO poisoning is not consistently seen.⁴ CO intoxication may contribute to the risk of myocardial infarction.^4,5

A strong correlation is present between carboxyhemoglobin levels and psychometric testing abnormalities.² Psychometric testing measures actual neurologic disability and may therefore better define carboxyhemoglobin poisoning severity than blood CO level.