Clinical and Interpretive

Measurement of carbon monoxide is useful in verifying carbon monoxide toxicity in cases of suspected exposure. Carbon monoxide (CO) poisoning causes anoxia, because CO binds to hemoglobin with an affinity 240 times greater than that of oxygen, thus preventing delivery of oxygen to the tissues. Twenty percent saturation of hemoglobin induces symptoms (headache, fatigue, dizziness, confusion, nausea, vomiting, increased pulse, and respiratory rate). Sixty percent saturation is usually fatal. This concentration is reached when there is 1 part CO per 1,000 parts air.

Carboxyhemoglobin diminishes at a rate of about 15% per hour when the patient is removed from the contaminated environment. The most common cause of CO toxicity is exposure to automobile exhaust fumes.

Significant levels of carboxyhemoglobin can also be observed in heavy smokers. Victims of fires often show elevated levels from inhaling CO generated during combustion. Susceptibility to CO poisoning is increased in anemic persons.