Types of Anemia Determinants
There are various types of anemia based on a number of different factors. One factor is the direct cause of the low red blood cell count – decreased RBC production, accelerated RBC destruction, or acute blood loss. Within these major groups there are secondary factors that define subcategories of types.
Decreased red blood cell production can be genetic or acquired. Acquired causes are primarily on the basis of chronic disease with inflammation or nutritional deficiency. Hastened erythrocyte destruction can also be hereditary or acquired. Acquired forms are commonly due to mechanical factors such as an enlarged spleen or autoimmunity. Pathological blood loss can be the result of disease or injury. Some forms of anemia have more than one cause and factor to consider
The size and the depth of the color of red blood cells also define the type of anemia. The terms for the types based on these parameters are microcytic, macrocytic, hypochromic, hyperchromic, or a combination depending on the MCV and MCH of the erythrocytes.
Anemia of chronic disease – Is a decrease in the number of erythrocytes in blood due to a state of chronic inflammation. The inflammation might be due to a number of causes. They include the following:
- chronic infection
- autoimmune and collagen vascular disease
- chronic diseases such as of the kidneys, liver or lungs
- critical bodily injuries
Additionally, the anemia due to chronic kidney disease is sometimes partially the result of decreased erythropoietin – a hormone biosynthesized in the kidneys primarily and in the liver to a lesser degree which regulates red blood cell production in the bone marrow. Treatment of many of these chronic diseases with it often improves the red blood cell count.
Aplastic anemia –Is a decreased red blood cell count due to the bone marrow’s inability to produce sufficient red blood cells to replace those lost through the process of natural death. There is also the decreased production of white blood cells and platelets. The cause is usually unknown. Some known causes though are exposure to certain chemicals or drugs, radiation, and autoimmunity. Fanconi anemia is a form of the disorder in which the bone marrow aplasia is of a genetic basis.
Cooley’s anemia (β–thalassemia major) – Is the reduced red blood cell count resulting from the lack of hemoglobin beta chain production. It is the most severe form of the disease affecting beta chain production. The reason is individuals with it are homozygous for the genetic defect that causes it. It is associated with a shortened lifespan.
Folate deficiency anemia – Is a decreased number of red cells in blood due to a lack of the B vitamin – folate which is necessary for red blood cell production. It is usually associated with hyperchromia. Common causes include:
- Insufficient dietary intake of the vitamin
- Decreased absorption of the vitamin from the intestinal tract
- Increase utilization of folate due to conditions such as pregnancy or chronic hemolysis
G6PD deficiency (glucose 6 phosphate dehydrogenase deficiency) – Is the lack of the enzyme, G6PD (glucose 6 phosphate dehydrogenase), which keeps red blood cells from breaking down under conditions of extreme stress, infection, or exposure to certain foods or drugs.
Hemolytic anemia – Is a reduced red blood cell count resulting from accelerated destruction of the cells. It can be hereditary or acquired. The mechanism of its production can be immune system mediated or based on mechanical trauma to the cells.
The most common and well understood hereditary hemolytic disorders are the following:
- hemoglobinopathy (sickle cell disease being the most common)
- thalassemia (of various types)
- G6PD deficiency
A rarer hereditary cause of hemolytic anemia is one in which the genetic defect causes instability of red blood cell membranes. There are many such disorders, of which hereditary spherocytosis is the prototype.
Acquired hemolytic anemia is often the result of the immune system’s production of antibodies which attack and cause the destruction of red blood cells. They might be autoantibodies or ones formed in response to exposure to certain antigens such as microbes or drugs.
Mechanical trauma to red cells is a common acquired cause of hemolysis. Common triggers include:
- Artificial heart valve(s)
- Disseminated intravascular coagulation (DIC)
- Malignant hypertension – severely elevated blood pressure that damages blood vessels
- Hemodialysis – the removal of toxins from the bloodstream via a machine that functions as a substitute for the kidneys
- Prolonged marching or marathon running that causes trauma to RBCs in vessels
Hyperchromic anemia – Is a generic term for a disorder of increased hemoglobin within red blood cells in the face of a reduced red blood cell count. Consequently, the cells stain darker than normal when viewed with a microscope.
Iron deficiency anemia – Is a form of anemia due to insufficient iron in the diet or chronic blood loss. Since the amount of hemoglobin produced is less because of the iron deficiency the RBCs are usually smaller than normal and pale in appearance.
Megaloblastic anemia – Is a form of macrocytic anemia characterized by megaloblasts. The two most common direct causes are vitamin B12 deficiency and fully acid deficiency.
Pernicious anemia – Is a disorder in which the body is unable to produce a sufficient number of healthy red blood cells because of the inability to absorb enough vitamin B12 from the intestines. The reason for the defect is a lack of intrinsic factor. It appears to be an autoimmune disease in that most people with it have antibodies directed against the stomach cells that produce the protein. It also has a more common than expected association with other autoimmune diseases.
Sideroblastic anemia – Is any of the group of blood disorders in which even though possessing sufficient amounts, the body is not able to use iron to make hemoglobin. In addition to a decreased red blood cell count iron accumulates in the bone marrow in the form of ringed sideroblasts. There are inherited and acquired types. It can also be idiopathic (cause unknown).
Thalassemic anemia – Is anemia due to thalassemia. The cause of the reduction in the red blood cell count is mainly decreased production of hemoglobin. But increased destruction from hemolysis also contributes.
Vitamin B12 deficiency anemia – Is a decreased number of red cells in blood due to a lack of vitamin B12 which is necessary for RBC production. The RBCs are usually larger than normal and stain deeper than normal. Pernicious anemia is a common form of it. It might also be due to a deficiency of vitamin B12 in the diet or other causes of its malabsorption.