When you finish this lecture, you will be able to:
Understand the physiologic causes of anemia
List the major types of anemia and describe their clinical and
morphologic features.
Formulate a differential diagnosis for anemia given a clinical setting, an
MCV, and a few salient morphologic features.
o v e r v i e w .
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
- infection (e.g., malaria)
- 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. Sometimes the cause of a patient's anemia is obvious. When the cause is unclear, however, it is helpful to have a quick and easy way to narrow down the possibilities. You can do this using the MCV and the RDW.
I. Microcytic anemias (MCV<80)
C. Anemias due to globin synthesis disorders
II. Macrocytic anemias (MCV>100)
III. Normocytic anemias
C. Anemia due to bone marrow failure
F. Anemia due to mixed etiologies (e.g., iron and B12/folate deficiencies)
