Classifications of Anemia
The main function of a red blood cell or erythrocyte is to carry and transport oxygen to the different parts of the body. The normal RBC count is 4-6 million/mm3. Hemoglobin (Hgb), an iron-bearing protein, is found inside an erythrocyte. Molecules of this iron containing protein are responsible for transporting the bulk of oxygen that is carried in the blood.
The more hemoglobin molecules the RBC contain, a higher amount of oxygen will they be able to carry. If the hemoglobin is defective, the erythrocyte will also malfunction. A red blood cell is just a vessel; the one that performs the oxygen transportation is the hemoglobin. Normal hemoglobin is 13-18 grams/dl in males and 12-16 grams/dl in females. A decrease in the RBC or hemoglobin or the oxygen-carrying ability of a blood is termed as anemia.
RBC’s are produced by the bone marrow a process known as erythropoiesis. Before a red blood cell is formed, the hematopoietic stem cell first produces an uncommitted stem cell to be formed to committed progenitor cell. Progenitor cells are not only the precursor of RBC, but also of lymphocytes and megakaryocytes (antecedent of platelets). Before an erythrocyte is formed the progenitor cells develop an erythroblast, then a reticulocyte, and finally erythrocyte (RBC). A hormone, erythropoietin, which is secreted by the kidney, also controls RBC production by stimulating the bone marrow.
Types of anemia
This type of anemia covers all condition where the bone marrow incapable of producing enough cells to develop to erythrocyte. Lack of erythropoietin may also be a contributing factor of the abnormality. The following types of anemia are under this classification:
- Aplastic anemia –In this condition, the precursor cells (stem or progenital cells, which is responsible in forming components of blood) are extremely deficient, thereby, production of all formed elements (including RBC, lymphocyte, megakaryocytes) are reduced. Because of the depressed bone marrow function, it is replaced by fat cells leading to anemia, excessive bleeding (thrombocytopenia) and infections (depressed WBC count). This type of anemia is also a common example of a pancytopenic disorder.
- Iron-deficiency anemia – It is also called microcytic, hypochromic anemia. This is type of anemia is the most common form among all ages, and is characterized by a low iron concentration in the body.
- Megaloblastic anemia – A macrocytic, normochromic anemia results as the essential factors (vitamin B12 and folic acid) for normal DNA synthesis are missing causing suppression of mitosis in the bone marrow and allowing the RNA or protein synthesis to take place for the progression of cell growth without cell division. The resulting cells remain enlarged (because mitosis is absent).
- 1. Vitamin B12 deficiency – Vitamin B12 or cobalamin is required for normal DNA synthesis. It is not synthesized in the tissues of but solely depends on the dietary intake of meat, liver, dairy products and sea foods.
- 2. Folic Acid Deficiency – folic acid is also important for the DNA synthesis of cells. The dietary sources of folate are meats, eggs, leafy vegetables which are easily available.
This type of anemia refers to the state where hemolysis (erythrocyte destruction) causes symptoms of anemia. Classification of this condition is further narrowed into intrinsic (inherited) or extrinsic (damage in erythrocyte is caused by environmental factors).
- Intrinsic Hemolytic Anemia
- Sickle Cell anemia – an inherited disorder on the beta chain of the hemoglobin resulting to abnormally shaped red blood cells. In this condition an abnormal hemoglobin S (HbS) is contained in the RBC’s causing distortions or sickling of the red blood cells.
- Thalassemia – group of genetic disorders that involve a defective hemoglobin- chain synthesis. Thalassemia major is threatening disease characterized by severe anemia, hemolysis and ineffective erythropoiesis. Thalassemia minor is a mild form of anemia. The affected individual has only one defective gene and is asymptomatic.
- Extrinsic Hemolytic Anemia
- Immune hemolytic anemia – a person’s own antibodies destroy his own red blood cells (hemolysis).
- Mechanical hemolytic anemia – hemolysis is caused by trauma or physical injuries that disrupt red blood cells altering and tearing them through the small vessels.