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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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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