Macrocytic anemia
| Macrocytic anemia | |
|---|---|
| Classification and external resources | |
| Specialty | hematology |
| ICD-10 | D52.9 |
| MeSH | D000748 |
The term macrocytic is from Greek words meaning "large cell". A macrocytic class of anemia is an anemia (defined as blood with an insufficient concentration of hemoglobin) in which the red blood cells (erythrocytes) are larger than their normal volume. The normal erythrocyte volume in humans is about 80 to 100 femtoliters (fL= 10−15 L). In metric terms the size is given in equivalent cubic micrometers (1 μm3 = 1 fL). The condition of having erythrocytes which (on average) are too large, is called macrocytosis. In contrast, in microcytic anemia, the erythrocytes are smaller than normal.
In a macrocytic anemia, the larger red cells are always associated with insufficient numbers of cells and often also insufficient hemoglobin content per cell. Both of these factors work to the opposite effect of larger cell size, to finally result in a total blood hemoglobin concentration that is less than normal (i.e., anemia).
Macrocytic anemia is not a disease in the sense of having a single pathology but, rather, is a condition. As such, it is the class name for a set of pathologies that all produce somewhat the same red blood cell abnormality. Many specific pathologies are known which result in macrocytic-type anemias. Some of these produce slightly different sets of appearances in blood cells that are detectable from red and white cell morphology, and others are only detectable with chemical testing.
Especially common causes of macrocytic anemias are the so-called megaloblastic anemias, in which cells are larger because they cannot produce DNA quickly enough to divide at the right time as they grow and thus grow too large before division. Causes of the DNA synthetic problem range from lack of certain vitamins needed to produce DNA (notably folate and B12), to poisons or inhibitors of DNA replication, such as some kinds of antiviral drugs and chemotherapeutic agents. Classically, these megaloblastic types of anemias are associated also with more specific features, such as megaloblasts in the bone marrow, the presence of ovalocytes in the (peripheral) blood smear, and the pathognomonic presence of hypersegmented neutrophils.
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