16. TYPICAL FORMS OF PATHOLOGY OF THE RED BLOOD CELL SYSTEM. ANEMIA. ERYTHROCYTOSIS

Typical disorders of the red blood cell system include anemia and erythrocytosis.

ANEMIA

Anemia may be defined as a reduction of total hemoglobin in the body usually accompanied by a decrease in concentration of hemoglobin in the peripheral blood. Anemia is often accompanied by a decreased number of red blood cells.

Classification of anemia based on its underlying mechanism is given in fig. 19.

Fig. 19

I. Due to blood loss.

•  Chronic.

•  Acute.

II. Hemolytic anemia.

•  Hereditary intrinsic abnormalities of red blood cells include:

 —   red cell membrane disorder;

 —   red cell enzyme deficiencies;

 —   disorders of hemoglobin synthesis (sickle-cell anemia, thalassemia).

•  Extrinsic abnormalities of red blood cells may be induced by the following:

 —   antibodies;

 —   mechanical trauma;

 —   infections, such as malaria;

 —   chemical injury;

 —   sequestration in mononuclear phagocyte system. III. Deficient erhythropoiesis.

•  Disturbances of proliferation and differentiation of stem cells.

•  Disturbances of proliferation and maturation of erythroblasts.

Anemia can also be classified according to the cell size and it is termed as normocytic, microcytic (MCV <80 fL) or macrocytic (MCV >95 fL). Depending on the content of hemoglobin in a single erythrocyte anemia may be normochromic, hypochromic (MCH <27 pg/RBC) and hyperchromic (MCH >33 pg/RBC). Mean cell volume detects macrocytosis or microcytosis. Variation in cell size is called anisocytosis and variation in cell shape is named poikilocytosis.

The normal reticulocyte count ranges from 0.3 to 1.2%. Increases in the reticulocyte count provide a reliable measure of the red cell production response to anemia. Therefore anemia may be hyporegenerative or regenerative. Maturation disorders show a low reticulocyte index with a macrocytic or microcytic morphology.