NBDE Quiz # 18
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1. Question
In methemoglobinemia, all of the following are true except:
Correct16. The correct answer is C. Methemoglobin levels may be obtained by both arterial and venous blood draws. Hemoglobin is oxidized to methemoglobin. Elevated levels of methemoglobin in the blood are caused when the mechanisms that defend against oxidative stress within the red blood cell are overwhelmed and the oxygen carrying ferrous ion (Fe2+) of the heme group of the hemoglobin molecule is oxidized to the ferric state (Fe3+). This converts hemoglobin to methemoglobin, which is a non-oxygen binding form of hemoglobin that binds a water molecule instead of oxygen. Patients with G6PD deficiency lack the production of sufficient amounts of NADPH, an oxidizing agent. Normally, the production of methemoglobin is reduced back to a normal state by protective enzymes such as cytochrome b5 reductase (major pathway), and to a lesser extent NADPH methemoglobin reductase, glutathione, and ascorbic acid
Incorrect16. The correct answer is C. Methemoglobin levels may be obtained by both arterial and venous blood draws. Hemoglobin is oxidized to methemoglobin. Elevated levels of methemoglobin in the blood are caused when the mechanisms that defend against oxidative stress within the red blood cell are overwhelmed and the oxygen carrying ferrous ion (Fe2+) of the heme group of the hemoglobin molecule is oxidized to the ferric state (Fe3+). This converts hemoglobin to methemoglobin, which is a non-oxygen binding form of hemoglobin that binds a water molecule instead of oxygen. Patients with G6PD deficiency lack the production of sufficient amounts of NADPH, an oxidizing agent. Normally, the production of methemoglobin is reduced back to a normal state by protective enzymes such as cytochrome b5 reductase (major pathway), and to a lesser extent NADPH methemoglobin reductase, glutathione, and ascorbic acid