Review Question - QID 108454

This presentation is most consistent with a diagnosis of hereditary spherocytosis. Hereditary spherocytosis is characterized by small red blood cells with less surface area leading to a round cell with no central pallor. These changes in RBC morphology result in an increased MCHC.

Fatigue and pale skin are usually indicative of anemia, a suspicion confirmed by the physical exam finding of conjunctival pallor. The peripheral blood smear help investigate for abnormal RBC morphology. Normal erythrocytes are red and biconcave, with central pallor comprised of about 1/3 of the red cell's diameter. However in this case, peripheral blood smear shows spherocytes, or round erythrocytes without central pallor. Spherocytes are present only in hereditary spherocytosis and immune-mediated hemolytic anemias. Hereditary spherocytosis may be caused by a mutation in RBC cytoskeletal proteins such as spectrin, ankyrin, or band 3, leading to membrane removal by splenic macrophages with subsequent hypertrophy of the spleen as seen in this case. The remnants of RBC processing are seen as small round RBCs with increased MCHC.

Figure A shows a peripheral blood smear with spherocytes, which are seen as small round RBCs without central pallor. The lack of central pallor also hints that the MCHC is higher in these RBCs.

Incorrect Answers:
Answer 1: Ferritin is a measure of total body iron stores. It is increased in anemia of chronic disease. This patient does not have a chronic state of inflammation and anemia of chronic disease does not explain the other findings in this case.

Answer 2: Haptoglobin is a serum protein that facilitates the removal of hemoglobin from the bloodstream by binding to it. Intrinsic hemolytic anemias such as hereditary spherocytosis would have a decreased level of haptoglobin due to the increased release of hemoglobin from hemolyzed RBCs.

Answer 3: Hematocrit is a measure of red blood cell volume as a proportion of total blood volume. Hematocrit is decreased in states of anemia as is present in this case.

Answer 5: MCV is a measure of the volume of RBCs. Increased MCV is seen in macrocytic anemias such as folate or B12 deficiency. MCV would be expected to be normal or decreased in hereditary spherocytosis.

Bullet Summary:
Hereditary spherocytosis presents as a hemolytic anemia in children and has RBCs without central pallor on peripheral blood smear. MCHC is increased in hereditary spherocytosis due to removal of membrane by macrophages in the spleen.