How is the clinical diagnosis of acute carbon monoxide (CO) toxicity confirmed?

Updated: Sep 18, 2018
  • Author: Guy N Shochat, MD; Chief Editor: Gil Z Shlamovitz, MD, FACEP  more...
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Answer

The clinical diagnosis of acute carbon monoxide (CO) poisoning should be confirmed by demonstrating an elevated level of carboxyhemoglobin (HbCO). Either arterial or venous blood can be used for testing. [3]

Analysis of HbCO requires direct spectrophotometric measurement in specific blood gas analyzers. Bedside pulse carbon monoxide (CO)-oximetry is now available but requires a special unit and is not a component of routine pulse oximetry. A 2012 study showed that noninvasive pulse CO-oximetry correlates with more rapid diagnosis and initiation of hyperbaric oxygen therapy than laboratory CO-oximetry. However, the impact on clinical outcome is still not proven. [23]  A 2017 clinical policy statement from the American College of Emergency Physicians (ACEP) recommends against using pulse CO-oximetry to diagnose CO toxicity in patients with suspected acute CO poisoning (level B recommendation). [24]  

Elevated CO levels of at least 3–4% in nonsmokers and at least 10% in smokers are significant. [3] However, low levels do not rule out exposure, especially if the patient already has received 100% oxygen or if significant time has elapsed since exposure. HbCO levels in cigarette smokers typically range from 3-5%, but may be as high as 10% in some heavy smokers. [3] Presence of fetal hemoglobin, as high as 30% at 3 months, may be read as an elevation of HbCO level to 7%. [25] Symptoms may not correlate well with HbCO levels.


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