Red Cell Disorders White Cell Disorders Bleeding Disorders Transfusion Medicine Red Cell Disorders

RED CELL DISORDERS Disorders of red cells can result in either anemia or polycythemia (an increase in the number of red cells). Anemia is a reduction in the oxygen-carrying capacity of blood, which usually stems from a reduction of the total circulating red cell mass to below-normal amounts. Classification of anemia a. etiologic classification 1. Excessive bleeding 2. Increased red cell destruction, or 3. Decreased red cell production. These mechanisms serve as a basis for classifying anemias. The decrease in tissue oxygen tension that is associated with anemia usually triggers increased erythropoietin production (the exception is that of anemia related to chronic renal failure, in which erythropoietin-producing cells in the kidney are lost). Increased erythropoietin production leads to compensatory hyperplasia of erythroid precursors in the bone marrow and, in severe anemias, the appearance of extramedullary hematopoiesis within the secondary hematopoietic organs (the spleen, liver, and lymph nodes). Anemia that results from acute bleeding or increased red cell destruction (hemolysis) leads to compensatory regeneration of red cells 5-8 times normal. The hallmark of increased marrow output is reticulocytosis, the appearance of increased numbers of newly formed red cells (reticulocytes) in the peripheral blood. In contrast, disorders of decreased red cell production (aregenerative anemias) are characterized by reticulocytopenia. b. Morphologic classification, which is based on the morphology of red cells; this is often correlates with the cause of their deficiency. Specific red cell features that provide etiologic clues include the 1. Cell size (normocytic, microcytic, or macrocytic) 2. Degree of hemoglobinization, which is reflected in the color of the cells (normochromic or hypochromic) 3. Shape of the cells These features are judged subjectively by visual inspection of peripheral smears (blood film) and are also expressed quantitatively through the following indices: Mean cell volume (MCV): the average volume per red cell, expressed in femtoliters (cubic microns) Mean cell hemoglobin (MCH): the average content (mass) of hemoglobin per red cell, expressed in picograms Mean cell hemoglobin concentration (MCHC): the average concentration of hemoglobin in a given volume of packed red cells, expressed in grams per deciliter Red cell distribution width (RDW): the coefficient of variation of red cell volume. In modern clinical laboratories, specialized instruments directly measure or automatically calculate the red cell indices. Adult reference ranges are shown in (Fig. 3-1) The clinical consequences of anemia These are determined by 1. The severity of the anemia 2. Its speed of onset, and 3. Underlying pathogenic mechanism. • If the onset is slow, adaptations take place that partially compensate for the deficit in O2 carrying capacity, such as increases in plasma volume, increased cardiac output, increased respiratory rate (manifested as shortness of breath), and red cell 2,3-diphosphoglycerate levels. These changes can largely reduces the effects