Carboxyhemoglobin Levels in Smokers

Cigarettes contain a multitude of harmful substances, one of which is carbon monoxide. When carbon monoxide is combined with hemoglobin, carboxyhemoglobin (COHb) is formed. Since carbon monoxide has a much higher affinity for hemoglobin than oxygen does, the carboxyhemoglobin levels are higher in those with more carbon monoxide exposure, such as smokers.


Smoking increases blood carboxyhemoglobin levels.

Hemoglobin is a protein molecule found in red blood cells.  It transports oxygen from the lungs to body tissue as well as ridding the tissue of carbon dioxide by carrying it to the lungs to be exhaled. A hemoglobin level is one of the measurements included in a complete blood count (CBC).  When carbon monoxide binds with hemoglobin to form carboxyhemoglobin, it reduces the efficacy of the hemoglobin and the capacity of the blood to transport oxygen.

Carboxyhemoglobin Blood Levels

Nonsmokers have a carboxyhemoglobin level of less than 15 percent.  Smokers, on the other hand, have levels ranging from 3 to 15 percent. A level of 10 percent is the point at which the average person will begin to experience mild signs of carbon monoxide poisoning. 

Dangers of Increased Carboxyhemoglobin

Increased carboxyhemoglobin blood levels caused by smoking results in a compensating increase in overall hemoglobin, which can mask conditions such as anemia.  Other conditions diagnosed on the basis of hemoglobin threshold levels can be missed and go untreated as well, including nutritional deficiencies, malignancies and inflammatory conditions. Lower exercise tolerance and increased risk for heart attack during exercise is also observed in individuals with elevated levels of carboxyhemoglobin. 

Reducing Carboxyhemoglobin Levels

The cessation of a smoking habit reduces smoking-related blood carboxyhemoglobin levels to near normal levels after as little as 12 hours after the last cigarette.  Regular aerobic exercise such as jogging also reduces carbon monoxide in smokers, but because of the increased risk for heart attack associated with smoking, check with your physician before commencing a new exercise regime.

About the Author

Nancy Lovering is a writer, photographer and teaching assistant. She took novel writing at Langara College and photography at British Columbia Institute of Technology. She obtained her teaching assistant certificate through Delta School District Continuing Education. She previously worked as an assistant controller while in the Certified General Accountants program, and has training in dog psychology through Custom Canine Teaching Ltd. in Vancouver, BC.

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