Review Question - QID 213630

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Hemoglobin C Evaluation Diagnostic QID: 213630 (M1.OMB.19.1)

QID 213630 (Type "213630" in App Search)

A 41-year-old man presents to his primary care physician with a 3-month history of dyspnea on exertion. He says that he recently started playing in a father-son recreational soccer league and realized that he begins to become short of breath almost immediately after starting to play. He says that he was never the most physically active person and currently works as an office secretary. He says that he became worried because he feels like his level of fatigue and shortness of breath is unusual for someone of his age. Physical exam reveals splenomegaly but is otherwise unrevealing. A peripheral blood smear is obtained and the results are shown in Figure A. Which of the following would most likely reveal the etiology of this patient's symptoms?

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Blood ferritin level

22%

2/9

Blood heavy metal levels

11%

1/9

Flow cytometry assay

0/9

Methemoglobin reduction test

22%

2/9

Protein electrophoresis

44%

4/9

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This patient who is experiencing fatigue and shortness of breath on exertion and who presents with splenomegaly and crystals on peripheral blood smear most likely has hemoglobin C disease, which can be diagnosed using protein electrophoresis.

Hemoglobin C disease is caused by a structural variant of normal hemoglobin where the glutamic acid at the 6 position of the beta chain is mutated to a lysine. This mutation leads to the crystallization of hemoglobin and results in a mild hemolytic anemia. This disease is similar to sickle cell anemia but is milder in presentation. Notably, this disease can be differentiated from other structural causes of anemia through hemoglobin electrophoresis where patients will have hemoglobin C rather than the normal hemoglobin A. Markers of hemolysis will also be elevated such as indirect bilirubin and lactate dehydrogenase.

Figure/Illustration A shows a peripheral blood smear with characteristic crystals as indicated by the black circles on the illustration. These crystals are classically seen in hemoglobin C disease.

Incorrect Answers:
Answer 1: Blood ferritin level is useful in analysis of iron-related anemias; however, iron deficiency anemia and anemia of chronic disease would present with microcytic red blood cells rather than crystals on peripheral blood smear.

Answer 2: Blood heavy metal levels are useful in diagnosing lead poisoning anemia or sideroblastic anemia; however, these diseases would present with sideroblasts rather than crystals on peripheral blood smear.

Answer 3: Flow cytometry assay would be useful in diagnosing paroxysmal nocturnal hemoglobinuria; however, this disease would present with dark urine after sleep and no crystals on peripheral blood smear.

Answer 4: Methemoglobin reduction test would be useful in diagnosing glucose-6-phosphate dehydrogenase deficiency; however, this disease would present with Heinz bodies inside red blood cells rather than red blood cells that are shaped like crystals.

Bullet Summary:
Hemoglobin C can be seen as crystals on peripheral blood smear and will have abnormal findings on hemoglobin electrophoresis.

ILLUSTRATIONS:

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