Classification of Anemia
Red Blood Cells Affected by Underproduction, Loss, or Destruction
Nov 8, 2008
Anemia is characterized by a deficiency and/or dysfunction in red blood cells (RBCs), which carry oxygen to all tissues in the body. This condition can have multiple acute and chronic effects, including but not limited to weakness, fatigue, shortness of breath with physical exertion, loss of appetite, menstrual problems, and heart failure. Anemia comes in many forms because of its many causes, which are broadly grouped into three categories: inadequate RBC production, blood loss, and RBC destruction.
Inadequate RBC Production
Like white blood cells and platelets, RBCs are produced in the bone marrow. RBCs also require certain nutrients for normal development. Therefore, anemia due to inadequate RBC production can occur with certain nutritional deficiencies and/or disrupted bone marrow.
For example, RBCs may become smaller than normal (microcytic) if they are deficient in iron or larger than normal (macrocytic) if they lack vitamin B12 or folate. RBCs that are normal in size (normocytic) may be less concentrated in the bloodstream due to bone marrow destruction from various causes, such as cancer and medications. Chronic kidney failure may also cause normocytic anemia because the kidneys produce erythropoietin, the hormone that stimulates RBC production by the bone marrow.
Blood Loss
If the body loses a large amount of blood, RBCs are produced to replace the loss of RBCs. This may keep the RBC count steady, but significant bleeding can lead to iron deficiency anemia. This is due to an increase of RBC production without a concurrent increase in iron intake.
Any source of bleeding that is acute and massive or chronic and gradual can lead to anemia. Common circumstances for blood-loss anemia include surgery, childbirth, and colon cancer. Of note, colon cancer often involves rectal bleeding that goes unnoticed, emphasizing the importance of colon cancer screening.
RBC Destruction
Lastly, anemia can result from destruction of RBCs within the bloodstream itself. This can occur with defects within the RBC itself (intrinsic causes) or factors outside of the RBC (extrinsic causes). Many of these are genetic in nature.
Congenital structural abnormalities of the RBC can produce elliptical or spherical RBCs (elliptocytosis and spherocytosis, respectively) that are prone to bursting. Defects in hemoglobin, either with altered structure (such as with sickle cell disease) or with portions of its structure missing (thalassemia), can also produce fragile RBCs. Other causes of RBC destruction include but are not limited to hyperactive destruction of RBCs by the spleen (hypersplenism) and antibodies against RBCs.
Final Words
The preceding is meant to be an overview of anemia and does not cover every single cause known. As with any online health information, it should not substitute for consultation with a physician.
References
- Merck Manual - Approach to the Patient With Anemia
- National Anemia Action Council - Anemia Monograph: General Overview
