A first step when diagnosing macrocytic anemia is to note the reticulocyte count. If the reticulocyte count is elevated, the most likely cause is the compensation of hemolytic anemia or recovery from blood loss. A high reticulocyte count will usually rule out any other cause of macrocytic anemia. Reticulocytes in megaloblastic anemias are typically low.
Features that are common to all megaloblastic macrocytic anemias are:
- low RBC count
- low hemoglobin
- elevated MCV (generally greater than 110 fL)
- increased RDW
- other cytopenias
- hypersegmented neutrophils
- oval macrocytes
- increased bilirubin
- increased lactate dehydrogenase (LDH)
- hyperplastic bone marrow
- decreased reticulocyte count
- decreased myeloid:erythroid ratio
It is important to note that since the defect in megaloblastic anemia is a decreased ability to synthesize DNA, other cell lines will be affected. Therefore, it is not uncommon to have other cytopenias besides anemia and morphological changes in the other cell lines. One of the classic hallmarks of megaloblastic anemia is the presence of hypersegmented neutrophils (more on this on the next page). The image to the right shows hypersegmented neutrophils and oval macrocytes.
The increased bilirubin and LDH and the hyperplastic bone marrow all reflect increased cell death in the bone marrow due to these abnormal morphologies.
