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11-27-2006, 04:06 PM
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Anemia Types

Anemia is generally defined as a reduction in the number or volume of circulating red blood cells (erythrocytes) or an alteration in hemoglobin. Technically, anemia is not a disease but a symptom of any number of disorders. There are over 400 types of anemia, but many of them are rare. Even more startling is the fact that, presently, more than half of the world’s population will experience some form of anemia in their lifetime.
Generally, the origin of anemia is classified as either nutritional or non-nutritional. Anemias of a nutritional origin are those that stem from a deficiency of some nutrient, mainly iron, vitamin B12, or folic acid (folacin or folate); but they can also result from a deficiency of other nutrients, including vitamins B2, B6, C, A, D, E, and K; as well as zinc, copper, calcium, and protein. The lack of certain enzymes can also cause anemia. Non-nutritional causes are those that produce a decreased development of the red blood cell (RBC) precursors, decreased erythropoiesis (erythrocyte formation), or an increase in the destruction of RBCs.
Anemia is frequently associated with scurvy and may be indicative of a folate deficiency (macrocytic) or an iron deficiency (hypochromic). Nevertheless, patients have responded well with just the addition of vitamin C alone, suggesting that there may be a role that ascorbate plays in the maintenance of normal pools of reduced folates. However, there is no real evidence to suggest that folate is ascorbate dependent. In the case of iron deficiency, though, it is known that adding vitamin C will increase iron absorption.
Anemias can be classified using two basic approaches:
etiology (pathophysiology): the causes of erythrocyte and hemoglobin depletion
morphology: the characteristic changes in the erythrocytes red blood cells (RBCs), size, shape, and color
An etiologic classification is based on the various conditions that can result from any of the physiologic changes and helps determine direction for planning care. A morphologic classification provides an orderly method for ruling out certain diagnoses when establishing a cause for a particular anemia.
Such morphologic changes in the red blood cell are described in this manner:
Cell size: (Terms that refer to cellular size end with "cytic".) normocytes (normal) microcytes (smaller than normal) macrocytes (larger than normal) anisocytes (various sizes)
Cell shape: poikilocytes (irregularly-shaped cells) spherocytes (globular cells) drepanocytes (sickle cells)
Cell color: (generally refers to the staining characteristics which reflects the hemoglobin concentration. Terms that describe hemoglobin content end with "chromic".) normochromic (sufficient or normal amounts of hemoglobin) hyperchromic (containing an unusually high concentration of hemoglobin in its cytoplasm) hypochromic (containing an abnormally low concentration of hemoglobin)
These changes produce the following categories of anemias:
Macrocytic-normochromic anemias (pernicious and folate-deficiency)
Microcytic-hypochromic anemias (iron-deficiency, sideroblastic, thalassemia)
Normocytic-normochromic anemias (aplastic, posthemorrhagic, hemolytic, chronic disease, sickle cell)
Macrocytic-normochromic anemia, also known as megaloblastic anemia, produces large, abnormally shaped erythrocytes but normal hemoglobin concentrations. The unusually large stem cells (megaloblasts) in the bone marrow mature into abnormally large erythrocytes (macrocytes) in the circulation. Megaloblastic stem cells are larger at all maturational stages than normal stem cells (normoblasts). In addition, the nucleus of the megaloblast is unusually small in relation to the size of the cell. As the cell matures and begins to synthesize hemoglobin, chromatin in the nucleus fails to clump normally, although the hemoglobin content remains normal. Defective DNA synthesis, caused by deficiencies of vitamin B12 or folate, produces a pattern of ineffective erythropoiesis (cell formation), causing premature cell death with reduced numbers of mature erythrocytes. It is unknown why such a deficiency would cause this outcome, but suggested mechanisms include a delay in nuclear maturation and an imbalance in the normal distribution of RNA and DNA. Nuclear functions or DNA replication and cell division are blocked or delayed. However, RNA and protein synthesis, both cytoplasmic functions proceed normally. The imbalance in the RNA/DNA ratio causes derangement of cell growth.
Microcytic-hypochromic anemia produces small, abnormally small erythrocytes and reduced hemoglobin concentrations. However, hypochromia can occur even in cells of normal size. This type of anemia results from a variety of conditions that are caused by disorders of iron metabolism, porphyrin and heme synthesis, or globin synthesis.
Normocytic-normochromic anemia produces a destruction or depletion of normal or mature erythrocytes. Although the erythrocytes are relatively normal in size and in hemoglobin content, they are insufficient in number. This type does not share any common cause, pathologic mechanism, or morphologic characteristics and is less common than the others. The five distinct anemic conditions exemplify the diversity of this classification.
Aplastic anemia (caused from depressed stem cell proliferation resulting in bone marrow aplasia)
Posthemorrhagic anemia (caused from an abnormal amount of blood loss)
Hemolytic anemia (premature destruction [lysis] of mature erythrocytes in the circulation)
Anemia of chronic disease (chronic infection or inflammation or malignancy causes an abnormally increased demand for new erythrocytes)
Sickle cell anemia (congenital dysfunction of hemoglobin synthesis causing abnormal cell shapes)Data used to identify anemia types include the erythrocyte indicators:
mean corpuscular volume (MCV), measures the average erythrocyte volume
mean corpuscular hemoglobin (MCH), measures the average amount of hemoglobin per erythrocyte
mean corpuscular hemoglobin concentration (MCHC), measures the average concentration of hemoglobin in erythrocytes. (See more under Lab Tests (http://www.innvista.com/health/ailments/anemias/labtests.htm).)
Anemias associated with decreased RBCs can occur for any number of reasons. Some anemias arise from failure or inability of the bone marrow to synthesize RBCs properly. Others occur because the body cannot synthesize or absorb a specific component necessary for RBC production. Such anemias resulting from a decreased production of RBCs include iron deficiency anemia, Vitamin B12 (pernicious) anemia, folic acid deficiency anemia, and aplastic anemia. Of those suffering from anemia, 20% are women and 50% are children.
Anemia is sometimes the first detectable sign of arthritis, infection, or certain major illnesses, including cancer. Drug use, hormonal disorders, chronic inflammation in the body, surgery, infections, peptic ulcers, hemorrhoids, diverticular disease, heavy menstrual bleeding, repeated pregnancies, liver damage, thyroid disorders, rheumatoid arthritis, bone marrow disease, and dietary deficiencies can all lead to anemia. There are also a number of hereditary disorders that cause anemia, especially sickle cell disease and thalassemia.
According to the Iron Institute, who gathered definitions from medical dictionairies and encyclopedias as well as the internet, anemia has a wide variety of definitions. Even though all of them are correct to some extent, none of them is a complete definition. The following are just a few which will explain why it is so difficult to umbrella over 400 anemias into one convenient description. Anemia is: <UL>a condition in which the number of RBCs is below normal
a reduction in total circulating RBC mass, diagnosed by a decrease in hemoglobin concentration
a hemoglobin level below 12 g/dl
any condition resulting from a significant decrease in the total body erythrocyte mass
a decrease in the circulating RBC mass and a corresponding decrease in the oxygen-carrying capacity of the blood
a decreased ability of RBCs to provide adequate oxygen supplies to body tissues
a reduction in the hemoglobin concentration to below 13.5 g/dl in an adult male and to below 11.5 g/dl in an adult female
any condition characterized by an abnormal decrease in the body’s total RBC mass
a condition in which either RBCs or the amount of hemoglobin (oxygen-carrying protein) in the RBC is low
a condition in which a person has inadequate amounts of iron to meet body demands
a decrease in the amount of RBCs in the blood caused by having too little iron
having fewer than the normal number of RBCs or less hemoglobin than normal in the blood
decreases in numbers of RBCs or hemoglobin content caused by blood loss, deficient erythropoiesis, excessive hemolysis, or a combination of these changes
a blood disorder that results from a shortage of hemoglobin in the RBCs, the disk-shaped cells that carry oxygen to all parts of the body
an abnormal reduction in RBCs
a condition when the amount of RBCs or hemoglobin becomes low, causing the tissues of the body to be deprived of oxygen-rich blood
a reduction in the number of RBCs in the body
a condition in which the blood is low on health RBCs