A n e m i a
Anemia is defined as a reduction below normal in hemoglobin or red blood cell count.
As you will see, there are many different types of anemia. One way to think about the anemias is to group them according to physiologic cause:
I. Anemias caused by blood loss
II. Anemias caused by excessive red blood cell destruction (hemolysis)
A. Extracorpuscular hemolytic disease
• autoimmune disorders
• infection (e.g., malaria)
• hypersplenism
• trauma to red blood cells
B. Intracorpuscular hemolytic disease
• hereditary membrane abnormalities
• hereditary globin synthesis abnormalities
III. Anemias caused by decreased red blood cell production
A. Bad diet (not enough iron, vitamin B12, or folate)
B. Decreased number of erythroblasts (as in aplastic anemia)
C. Bone marrow full of things besides hematopoietic precursors (e.g., tumor)
D. Chronic disease (e.g., renal disease, inflammatory disease)
E. Cirrhosis
Another way to think about the anemias is to group them morphologically (in other words, according to how they appear under the microscope): anemias with little (microcytic) red cells, anemias with big (macrocytic) red cells, and anemias with normal-sized (normocytic) red cells. I find it helpful to think about the anemias in this manner, because while sometimes the cause of a patient's anemia is obvious, often it is not. In these undiagnosed cases, it is helpful to have a quick and easy way to narrow down the possibilities.
I. Microcytic anemias (MCV<80)
II. Macrocytic anemias (MCV>100)
III. Normocytic anemias
