COHB is Hb with carbon monoxide (CO) instead of the normal oxygen bound to it. CO has a much great affinity than oxygen for Hb. The source of the CO may be exhaust (such as from a car, truck, boat, or generator), smoke from a fire, or tobacco smoke. COHB is formed in CO poisoning. The COHB level is useful in judging the extent of CO 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, angina, and MI. Physiologically, COHB levels increase due to hemolysis. CO is a natural by-product of the breakdown of protoporphyrin to bilirubin.
Normal range:
Nonsmokers: 0.5 " “1.5% saturation of Hb
Smokers (1 " “2 packs/day): 4 " “5%
Heavy smokers (>2 packs/day): 8 " “9%
Use
Verifying CO toxicity in cases of suspected exposure
Interpretation
Increased In
CO poisoning
Hemolytic disease
Blood in the intestine
Reactions of intestinal bacteria
Calorie reduction
Following exercise
Methylene chloride toxicity (found in paint removers)
Limitations
COHB 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 COHB 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.