Part II • Red Cell Disorders
Figure 7.7 Hereditary xerocytosis.
Figure 7.6 Stomatocytes.
show crenation and hemolysis at 49°C, but red cells from patients with HPP will fragment at 46°C. Some may even fragment at 37°C, body temperature, with prolonged heating. Individuals with this disorder will have severe hemolysis, poor growth, and facial abnormalities due to the expanded bone marrow mass. The MCV is extremely low with a range of 50 to75 fL.13
Hereditary stomatocytosis is a rare hemolytic disorder in which the red cells have an intrinsic defect related to sodium and potassium permeability. The defect, which is autosomal dominant, is identified as a deficiency in the membrane protein, stomatin, thought to regulate ions across the red cell channel.14 Because of this transport lesion, the intracellular sodium content increases, leading to increased water content and a mild decrease in intracellular potassium. The red cell swells and take on a morphology that appears as if the red cells have slits or bars in the center, as if the cell is "smiling." Peripheral smears show 10% to 30% stomatocytes (Fig. 7.6) with an elevated MCV and decreased MCHC. Patients will show a mild, moderate, or marked anemia that can be corrected by splenectomy, a dangerous procedure in this disorder because many patients have thrombotic complications.15 Stomatocytes may also be seen in individuals with Rh null disease—those individuals who lack Rh antigens. These patients show a moderate anemia with a combination of spherocytes and stomatocytes.
Hereditary xerocytosis (Fig. 7.7) is a rare autosomal dominant condition in which red cells have an increased surface-to-volume ratio, leading to moderate to severe anemia, a decreased osmotic fragility, and high MCHC.16
Red cells are markedly dehydrated and show an irreversible potassium loss and formation of xerocytes, a peculiar red cell morphology where the hemoglobin of red cells seems puddled at one end of the red cell. The etiology of this disorder is unknown.
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