What is the role of methemoglobin levels in the diagnosis of cyanide toxicity?

Updated: May 30, 2020
  • Author: Inna Leybell, MD; Chief Editor: Michael A Miller, MD  more...
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A methemoglobin level is especially important in cyanotic patients. The presence of methemoglobin suggests that little or no free cyanide is available for binding, because methemoglobin vigorously binds cyanide to form cyanomethemoglobin (which is not measured as methemoglobin).

Methemoglobin concentrations provide a guide for continued therapy after the use of methemoglobin-inducing antidotes, such as sodium nitrite. Elevated levels of methemoglobin (>10%) indicate that further nitrite therapy is not indicated and, in fact, may be dangerous.

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