Pearl 1: A good way to think (and teach) about microcytic anemia is to consider the ways in which microcytosis occurs. RBCs become microcytic due to a lack of hemoglobin, which can result from:
- Lack of iron (iron deficiency, anemia of chronic inflammation)
- Defects in heme synthesis (sideroblastic anemias)
- Defects in the production of hemoglobin protein (thalassemias and hemoglobinopathies)
Pearl 2: Remember that in thalassemia (unlike iron deficiency and anemia of chronic inflammation), the RBC count may be normal or elevated, since the bone marrow is making large numbers of small cells.
See the attached review article from the NEJM for more on microcytic anemia!