MCQ Hematology Answer 26

The Correct Answer is D


Explanation:

Recognize an individual with methemoglobinemia who has been exposed to an offending agent. Rapid development of extreme dyspnea and cyanosis, in the setting of no hypoxia, should be the clue to consider methemoglobinemia. In this case, the patient was exposed to two different known medications (pyridium and sulfamethoxazole) associated with increased levels of methemoglobin in susceptible individuals.

Methemoglobin is the derivative of hemoglobin, in which the iron of the heme group is oxidized from the ferrous to the ferric state. It is the oxidation status that determines the oxygen-carrying capacity of hemoglobin. When iron is in the ferrous form (deoxyhemoglobin), oxygen can easily bind, in contrast to the inability to bind to the ferric hemes of methemoglobin.

Steady-state methemoglobin levels in the blood are usually <1% but can increase markedly when susceptible individuals (heterozygotes for methemoglobin reductase deficiency) are exposed to certain medications or chemicals. Correct therapy is prompt institution of methylene blue, to which individuals will respond rapidly with resolution of cyanosis.

Category: Hematology MCQs