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Red cell morphology can be defined as the appearance of the erythrocytes on a Wright's stained smear.
Careful examination of the red cells for the purpose of identifying abnormalities is part of the differential procedure. This examination is important because it may provide valuable diagnostic information to the physician, as well as provide a quality control mechanism to verify red cell indices values as determined by automated or manual methods.
Since RBC morphology plays such a crucial role in the discussion of anemia, it is important to understand the terms that describe morphologic variations. In a healthy individual, RBCs appear in a Wright stained smear as circular, pink discs. Each disc has a central pallor caused by the cell's biconcave sides. Poikilocytosis refers to any variation in shape. Oval, teardrop, helmet, pear, saddle and irregular-shaped cells may be seen in a single case of anemia.
Target cells are thinner than normal RBCs and, upon Wright stain, show a peripheral rim of HGB and a central HGB-containing area. This 'bull's eye' effect is the result of an increased surface/volume ratio. Target cells are found in obstructive jaundice, following splenectomy, in some classes of anemia, and in hemoglobin C disorder.
Spherocytes are nearly round RBCs, in contrast to the normal biconcave discs. They have a smaller diameter and lack the usual central pale area. They are found in hereditary spherocytosis, some autoimmune hemolytic anemias, and after direct physical or chemical injury to the RBCs. In all these cases, tiny bits of the surface membrane have been removed, leaving the cell with a decreased surface/volume ratio.
Normal RBCs are nearly uniform in size, ranging from 6-8 microns in diameter. Anisocytosis is a general term referring to size variation. Macrocytosis and microcytosis are more specific, describing large and small cell populations.
The pink color of RBCs is due to acidophilic HGB within the cells. The intensity of color is proportional to the amount of HGB and is described by the terms normochromic, hypochromic and hyperchromic. In hypochromia, MCH and MCHC are usually decreased; the central pallor becomes larger and paler. In hyperchromia the RBCs are larger, hence thicker, and stain more deeply with less central pallor; the MCH is higher, but the MCHC (which corrects for size) is normal. In hereditary spherocytosis the cells are also hyperchromic, but the MCH is normal and the MCHC is increased because of the reduced surface/volume ratio.
Polychromia refers to the blue-gray appearance of newly released RBCs, which retain residual RNA for the first day or two of peripheral circulation. (Basophilic RNA stains blue, acidophilic HGB stains pink.) These young polychromic cells are larger and often lack the central pallor. Basophilic stippling refers to larger bits of retained RNA. When stained supravitally, these cells prove to be reticulocytes.
All information on this page is intended for your general knowledge only and does not provide medical advice, diagnosis or treatment.