What is the role of co-oximetry in the workup of methemoglobinemia?

Updated: Dec 09, 2018
  • Author: Mary Denshaw-Burke, MD, FACP; Chief Editor: Emmanuel C Besa, MD  more...
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Answer

Co-oximetry should be performed if available. The co-oximeter is an accurate device for measuring methemoglobin and is the key to diagnosing methemoglobinemia. It is a simplified spectrophotometer that can measure the relative absorbance of 4 different wavelengths of light and thus is capable of differentiating methemoglobin from carboxyhemoglobin, oxyhemoglobin, and deoxyhemoglobin. Newer co-oximeters can also measure sulfhemoglobin, which can be confused with methemoglobin by older devices.

Availability of appropriate equipment may be a problem. Lipemic specimens may result in a falsely elevated methemoglobin level. In addition, the presence of methylene blue interferes with the accurate measurement of methemoglobin by co-oximetry, hence this method cannot be used to monitor methemoglobin levels after treatment with methylene blue is initiated. Blood substitutes can cause co-oximetry to yield unreliable results.


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