Obtain a careful history of neurologic and cardiac symptoms consistent with CO poisoning and ask about sick housemates or pets and possible sources of CO exposure. Note that the most common symptoms include headache, dizziness, weakness, and nausea.
Use the physical exam to confirm neurologic or cardiac signs and to exclude alternative diagnoses and concomitant illnesses.
Determine levels of blood carboxyhemoglobin; confirm CO exposure in nonsmokers with levels greater than 3% and in smokers with levels greater than 10%.
Check other diagnostic tests, including ECG, ABG, and chest x-ray, to assess complications and concomitant problems.
Do not use CO levels from noninvasive pulse oximeters to rule out CO poisoning.
Use neuroimaging in patients in whom alternative diagnoses are likely but not as a primary diagnostic test for CO poisoning.