We are continuing the last topic, where one important type of morphologic changes was missing. 😊
Any variation in the shape of erythrocytes is called POIKILOCYTOSIS. When many different shapes are seen in the blood film, the general term is used. Otherwise we have more specific terms, and it is good to be as specific as possible in describing changes, because certain types are associated with certain diseases. Abnormal shapes which are not disease specific may also be significant and suggest further investigation.
Spherocytes are darkly stained spherical erythrocytes without central pallor. They appear small but have normal volume. Spherical shape is a consequence of reduction in the cell membrane, which results from partial phagocytosis because of surface-bound antibodies or complements. It makes cells less deformable and osmotically fragile. Spherocytes are rarely recognized in cats because of small size and lack of central pallor in their normal erythrocytes. Presence of spherocytes suggests immune-mediated hemolytic anemia (IMHA), but they can be also seen after blood transfusion with mismatched blood and have been reported in dogs with bee sting and zinc toxicity.
- ECHINOCYTES (BURR CELLS)
Echinocytes are regularly spiculated erythrocytes with numerous short, evenly distributed surface projections, that are uniform in size and shape. They can be an artifact from a change in pH during slow drying of blood film but are also associated with renal disease, lymphoma, chemotherapy (doxorubicin toxicosis) and snake envenomation.
- ACANTHOCYTES (SPUR CELLS)
Acanthocytes are irregular, spiculated erythrocytes with few, unevenly distributed surface projections of variable length and diameter. They result from changes in cholesterol or phospholipid concentrations in the erythrocyte membrane and are often observed on blood smears of cats with hepatic lipidosis or dogs with diseases of capillary beds – hemangiosarcoma, hemangioma, diffuse liver disease, vasculitis.
In eccentrocytes, oxidative damage causes fusion of opposing cell membranes on one edge of the cell and hemoglobin squeezing into a smaller volume toward the side. This results in loss of normal central pallor and a clear zone outlined by a membrane. Compressed hemoglobin appears eccentric and darker than normal. Eccentrocytes are associated with oxidative injury, following exposure to oxidative drugs or chemicals and may be found together with Heinz bodies.
- SCHISTOCYTES (FRAGMENTS)
Schistocytes are irregular erythrocyte fragments, that result from mechanical intravascular trauma. They can be observed with disseminated intravascular coagulopathy – DIC and other microvascular angiopathies, splenic neoplasia (hemangiosarcoma), IMHA, thrombosis, glomerulonephritis, valvular heart disease, doxorubicin toxicosis, iron deficiency …
Iron deficient erythrocyte can develop vacuole from oxidative injury. When these lesions enlarge and break open, they form a cell with spicules, which are termed keratocytes. The projections from the keratocytes can fragment and form schistocytes.
- CODOCYTES (TARGET CELLS)
Codocytes are bowl-shaped erythrocytes with a dense central area of hemoglobin that is separated from the peripheral hemoglobin rim by a pale zone. The shape is a consequence of increased cholesterol to phospholipid ratio within the cell membrane. They can be seen with a variety of conditions – regenerative response, corticosteroid therapy, iron deficiency, liver disease with cholestasis, splenectomy.
Stomatocytes are uniconcave erythrocytes with a mouth-like clear area near the cell center. Presence of only few on the blood film is insignificant, but hereditary stomatocytosis has been reported in dog breeds like Alaskan malamute and miniature schnauzer.
Thrall M. A., Weiser G., Allison R. W., Campbell T. W.: Veterinary Hematology and Clinical Chemistry, 2nd Ed. Wiley-Blackwell, 2012
Day M. J., Kohn B.: BSAVA Manual of Canine and Feline Haematology and Transfusion Medicine, 2nd Ed. BSAVA, 2012