Methemoglobin absorbs light at wavelengths that also absorb deoxyhemoglobin and oxyhemoglobin. Thus, methemoglobin interferes with the colorimetric testing that is used to obtain the percentage of oxyhemoglobin to deoxyhemoglobin. These may be helpful in determining the degree of tissue hypoxia and end-organ dysfunction. Urine pregnancy tests should be performed in females of childbearing age. Clinical recognition is paramount, as patients may have only vague complaints.
Treatment is determined by symptomatology.
Healthy asymptomatic patients without evidence of end-organ damage may require only observation. Supplemental oxygen Methylene blue is the first-line antidotal agent. Hyperbaric oxygen therapy or packed RBC exchange transfusions are alternative therapies for patients who are not candidates for methylene blue. Repeated doses of methylene blue in such instances may result in hemolysis. Methylene blue is ineffective for the treatment of sulfhemoglobinemia.