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Part II • Red Cell Disorders hypochromia, because these morphological clues can aid in determining if the macrocytosis is megaloblastic or nonmegaloblastic. Megaloblastic macrocytes are large and oval, with a thicker exterior membrane and lacking hypochromia. Macrocytes in the peripheral smear that lack any of these characteristics are usually not of megaloblastic origins. Several conditions can contribute to a macrocytic blood picture without a deficiency in vitamin B12 and folic acid. The most frequently seen conditions are a compensatory bone marrow response to hemolytic anemia, in which case a reticulo-cytosis will be seen. Because reticulocytes are polychro-matophilic macrocytes and because reticulocytes will be prematurely delivered from the bone marrow in response to hemolysis, it is easy to understand how a macrocytic blood picture would develop. Usually, in these cases, the MCV is only slightly elevated, up to 105 fL. Macrocytosis may also be seen in conditions such as hypothyroidism, chronic liver disease, alcoholism, chemotherapy treatment, or a myelodysplastic disorder. Often, in patients with chronic liver disease and alcoholism, the macrocytes are targeted or hypochromic. Additionally, a macrocytic blood picture is noted in newborns because their bone marrow is immature and rapidly delivering nucleated cells and reticulocytes. For a differential diagnosis of macrocytes, see Figure 6.6.

Differential Diagnosis of Macrocyte

Seen in:

- Folic acid deficiency

- Vitamin B12 deficiency

- Pernicious anemia

Oval macrocyte

Seen in:

- Folic acid deficiency

- Vitamin B12 deficiency

- Pernicious anemia

Oval macrocyte

Seen in:

- Alcoholism

- Hypothyroidism

- Liver disease

Round hypochromic macrocyte

Seen in:

- Alcoholism

- Hypothyroidism

- Liver disease

Round hypochromic macrocyte

Seen in:

-Neonate response to anemic stress -Response to anemic stress

Blue-tinged macrocyte

Seen in:

-Neonate response to anemic stress -Response to anemic stress

Blue-tinged macrocyte

Figure 6.6 Not all macrocytes are the same. This drawing depicts three types of macrocytes, each differentiated by how they are produced with respect to the clinical condition.

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