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Macrocyte Information and Courses from MediaLab, Inc.

These are the MediaLab courses that cover Macrocyte and links to relevant pages within the course.

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Alpha Thalassemia
A peripheral blood smear made from an EDTA-anticoagulated blood specimen revealed the following results when stained with Wright-Giemsa stain and viewed with 1000X magnification. What red blood cell morphologies are indicated by the arrows?View Page

Red Cell Disorders: Peripheral Blood Clues to Nonneoplastic Conditions
Conditions suggested by the macrocytes and the neutrophil in the photograph to the right include which of the following?View Page

Red Cell Morphology
Using the lymphocyte as a guideline, the cells that are indicated by the arrows would be described as what type of cells?View Page
Pseudomacrocytes

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Pseudomacrocytes

Pseudo macrocytes, as well as some microcytes, can be seen in this slide. Notice that pseudomacrocytes do not have the oval appearance seen in some megalocytes.

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The red blood cells indicated by the arrows have diameters greater than 9 µm and decreased central pallor. How would you report these cells?View Page
The cell in the center of this slide would be a:View Page
Another Example of Macrocytosis

This peripheral blood smear is from a patient with vitamin B-12 deficiency anemia (pernicious anemia), which results from an inability to absorb the vitamin B-12 needed for DNA synthesis. Since many cells are destroyed in the bone marrow, decreased numbers of red cells are present in the circulating blood, resulting in anemia. However, the red cells that are present are generally macrocytes and are filled with hemoglobin.

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Summary of Macrocytes

To summarize, two types of macrocytes can be seen, true macrocytes (megalocytes) and pseudomacrocytes. The MCV and MCH values will be increased when true macrocytes are present, while all the indice values will be normal when pseudomacrocytes are found.

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Megalocytes (macrocytes) are characterized by: (Choose ALL of the correct answers)View Page
Size Variation

Red blood cells can vary in size (diameter/volume) from smaller than normal, microcytes, to larger than normal, macrocytes. When red cells of normal size, microcytes and macrocytes are present in the same field, the term anisocytosis is used. Since the purpose of this unit is to acquaint you with the appearance (identification) of abnormal red cell morphology, percentages of abnormalities present will not be considered. It is important to be aware that rating red cell morphology for the purpose of reporting it is a skill which must be learned before you are able to complete this aspect of a differential count.

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Macrocyte

Macrocytes have a diameter of 9-14 µm (1.5 to 2 times larger than normal red cells) and the MCV is >100 fL. Several macrocytes are indicated by the blue arrows in the top image on the right. By comparison, macrocytes are larger than the nucleus of a normal lymphocyte. Macrocytes are frequently oval; two examples are indicated by the red arrows in the top image on the right.Oval macrocytes are most commonly associated with vitamin B-12 and/or folic acid deficiency. Decreased DNA synthesis causes the nucleus in the developing red cells to mature at a slower than normal rate. Since hemoglobin production is not affected, the mature red cell that is larger than normal is filled with hemoglobin, resulting in cells with little central pallor. Note that polychromatophilic red cells may also be larger than normal RBCs. However, if stained with a supravital stain, it would be obvious that these cells are reticulocytes. From a Wright-stained smear, they would be reported as polychromatophilic RBCs and not macrocytes. Examples of polychromatophilic RBCs are indicated by the arrows in the bottom image on the right. The cells stain gray-blue with Wright stain.

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Color of Erythrocytes

The staining characteristics of an RBC reflect the hemoglobin concentration in the cell as well as the maturity of the cell. RBCs with normal hemoglobin concentration and normal staining characteristics are described as normochromic. Slightly immature, non-nucleated red cells (reticulocyte stage) appear blue/gray on Wright-stained smears due to the presence of residual ribonucleic acid (RNA). The terms used to describe these cells are polychromasia or polychromatophilia. Polychromatophilic cells are frequently larger in size than mature red cells and can be distinguished from macrocytes by this distinctive color.

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Hypochromia and Hyperchromia

RBCs that are hypochromic have decreased amounts of hemoglobin. An MCHC <32 g/dL reflects this condition, which is illustrated in the upper image on the right. Hyperchromia means increase in color. The only cells that are truly hyperchromic are spherocytes. Spherocytes are the only cells that contain more hemoglobin than normal in relation to the cell volume.The arrows in the lower image on the right point to spherocytes.Cells located in the "too thin" portion of the smear may appear to be hyperchromic, however, this is an artifact. Macrocytes, which appear to have increased amounts of hemoglobin, have an MCHC value within normal limits, indicating that the cells, although larger than normal, are normochromic.

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White Cell and Platelet Disorders: Peripheral Blood Clues to Nonneoplastic Conditions
A most useful follow-up test to consider when faced with hypersegmented neutrophils and oval macrocytes (see image) in a peripheral blood smear is:View Page


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