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Chapter: Pathology: Red Blood Cell Pathology: Anemias

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Anemias

Anemia is a reduction below normal limits of the total circulating red cell mass.

ANEMIAS

Anemia is a reduction below normal limits of the total circulating red cell mass. Signsof anemia include palpitations, dizziness, angina, pallor of skin and nails, weakness, claudication, fatigue, and lethargy.

·            Reticulocytes are immature, larger red cells (macrocytic cells) that are spheri-cal and have a bluish color (polychromasia) due to free ribosomal RNA. Reticulocytes do not have a nucleus; note that any erythrocyte with a nucleus (nRBC) in peripheral blood is abnormal. Reticulocyte maturation to a mature erythrocyte takes about 1 day. The reticulocyte count is the percentage of red immature cells present in peripheral blood (normal 0.5–1.5%).

The corrected reticulocyte count takes into consideration the degree of anemia and is calculated as (patient’s hct/45) × (reticulocyte count); the idea behind the calculation is to scale the reticulocyte count by multiplying by the ratio of the patient’s hematocrit to “normal” hematocrit of 45%. When interpreting the corrected reticulocyte count, <2% indicates poor bone marrow response and >3% indicates good bone marrow response.

·            The reticulocyte production index is the corrected reticulocyte count/2; use this measure if bone marrow reticulocytes (shift cells) are present (polychro-masia). The division by 2 is because shift cells take twice as long as reticulo-cytes to mature (2 days versus 1 day).

Classification of anemia can be based on color: normochromic anemias have nor-mal red cell color (central pallor of about a third the diameter of the erythrocyte); hypochromic anemias have decreased color (seen as an increased central pallor of erythrocyte); and hyperchromic anemias, while theoretically possible, are usually instead called spherocytosis and have increased color (loss of central pallor of eryth-rocyte). Classification of anemia can also be based on size (MCV).


The pathogenesis of anemia varies with the underlying disease. Blood loss can cause anemia. Hemolytic anemias are also important, and include hereditary spherocyto-sis, glucose-6-phosphate dehydrogenase deficiency, sickle cell disease, hemoglobin C disease, thalassemia, and paroxysmal nocturnal hemoglobinuria. Immunohe-molytic anemias, which are hemolytic anemias with an immune component to thepathology, include autoimmune hemolytic anemia (AIHA), cold AIHA, incompat-ible blood transfusions, and hemolytic disease of the newborn. Anemias of dimin-ished erythropoiesis include megaloblastic anemia (B12 and folate deficiencies),iron deficiency anemia, anemia of chronic disease, aplastic anemia, myelophthisic anemia, and sideroblastic anemia.


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