Abbreviation: COHb
A hemoglobin molecule whose binding site is occupied by carbon monoxide (which binds with much higher affinity than oxygen). Carboxyhemoglobinemia (i.e., carbon monoxide toxicity) causes fatigue, headache, nausea, chest pain, respiratory failure, seizures, and coma. Chronic smokers can have baseline carboxyhemoglobin levels of 10-15%.