These are red blood cell fragments that are formed as a result of shearing of the cell by fibrin strands. This occurs when red blood cells rapidly pass through microvasculature that is lined or meshed with strands. Schistocytes can be seen with disseminated intravascular coagulopathy (DIC), also in animals with hemangiosarcoma and in animals with iron deficiency.
Acanthocytes: (spur cell)
The term acanthocyte is derived from the Greek word “acanthi” meaning “thorn” Acanthocytes are cells with five to ten irregular, blunt, finger-like projections. The projections with vary in width, length and surface distribution. These cells are seen in animals with altered lipid metabolism such as cats with hepatic lipidosis or dogs with liver disease.
Echinocyte: (burr cell)
Echinocytes have multiple, small, delicate regular shaped spines evenly distributed around the cell and are indistinguishable from artificially crenated cells. Echinocyte formation can be artificial, often seen with slow drying blood films or if the EDTA tube was underfilled. This artifact is then termed crenation. Echinocytes have been associated with renal disease, lymphosarcoma and rattlesnake bites in dogs. They can been seen after exercise in horses.
Drepanocyte: (sickle cell)
These cells are crescent shaped with pointed ends. Drepanocytes are often seen in normal blood of deer and goats. It is thought to be a result of low oxygen tension.
Keratocytes: (helmet cell)
Also called blister cells or bite cells. Keratocytes are associated with trauma especially cellular damage from contact with fibrin strands. One theory is the cell becomes impaled on a fibrin strand and the blood flow causes it to bisect. The second theory is that the opposing sides of the cell adhere to one another around the fibrin strand and when blood flows it frees the cell and the opposing sides rejoin, forming a pseudovaculole. Cells with pseudovacuoles are called blister cells or pre-keratocytes. When the vacuole ruptures (usually within minutes) the remaining cell resembles a helmet with straps or a horned cell.
Spherocytes are not easily detected in species other than dogs. Spherocytes are small, spherical red blood cells that are approximately two-thirds the diameter of normal red blood cells. They are densely hemoglobinized and lack central palor. In thick areas of the blood smear and near the feathered edge, all red blood cells may appear to be spherocytes, therefore, spherocytes should only be identified in the monolayer area of the blood film. Spherocytes are most commonly associated with immune-mediated hemolytic anemias. Antibodies form either to a foreign antigen that resembles the erythrocyte membrane or the antibodies attach to the erythrocyte membrane, marking them for destruction by macrophages. Spherocytes can also be seen after a transfusion with mismatched blood.
This is a group of cells characterized by an increased membrane surface area.
Target cells have the appearance of a target with a bullseye. They have a central, hemoglobinized area surrounded by an area of pallor and the periphery of the cell contains a band of hemoglobin.
Folded cells have a transverse, raised fold extending across the center of the cell.
Stomatocytes have a clear slit like pale region in the center of the cell. Both folded and stomatocytes are considered an artifact if the areas of pallor are all perpendicular to the feathered edge.
These are bowl shaped erythrocytes that form as a loss of membrane flexibility that does not allow the cell to return to a normal shape after passing through a capillary. They can occur due to lowed hemoglobin concentration or as an artifact.
Dacryocytes: (tear drop cells)
These tear drop shaped cells are seen in myeloproliferative diseases. These cells can be produced as an artifact but can be identified by the direction of their tail. Dacryocytes produced as an artifact have their tails pointing in the same direction.
Nucleated red blood cells:
Nucleated red blood cells (NRBC) usually represent early release of immature red blood cells during anemia.
These cells have small dark blue bodies within the erythrocyte. This represents residual RNA. It is common in immature red blood cells seen in cats. It is also characteristic of lead poisoning in dogs.
Howell Jolly Body:
These are nuclear remnants seen in young erythrocytes during a response to anemia. As cells containing nuclear remnants pass through the spleen, phagocytic cells remove the remnants. Howell Jolly Bodies are commonly seen in animals who have under gone a splenectomy.
These are round structures representing denatured hemoglobin caused by certain oxidant drugs or chemicals. The denatured hemoglobin attaches to the cell membrane and appears as a pale area. Unlike other animals, cats have Heinz bodies in as many as 5% of their red blood cells. Heinz bodies are increased with diseases such as lymphosarcoma, hyperthyroidism and diabetes mellitus in cats.
These are immature red blood cells that contain organelles (ribosomes) that are lost in the mature cell. Cats have two forms of reticulocytes. The aggregate form contains large clumps of reticulum. The punctate form, unique to cats, contains two to eight singular granules. In normal, non-anemic cats approximately 4% of the red blood cells are aggregate reticulocytes and 1.5 – 10% of the red blood cells are punctate reticulocytes.
A reticulocyte count is an expression of the percentage of red blood cells. A reticulocyte count should be preformed on all anemic animals. A reticulocyte count is useful in assessing the bone marrow’s response to anemia.
A variety of ehrlichia species are capable of infecting dogs. The brown dog tick transmits the organism and it appears as small clusters called morulae. The disease may result in neutropenia, thrombocytopenia and anemia. Clinical signs of ehrilichiosis include fever, depression, bilateral mucopurulent ocular discharge accompanied by photophobia, nasal discharge that is first serous and later purulent and spenomegaly. Canine ehrlichiosis is often masked or confused with other diseases such as Rocky Mountain spotted fever.
Haemobartonella felis is a fairly common parasite of feline erythrocytes. This disease is referred to as either Haemobartonellosis or feline infectious anemia. The organisms appear as small rod-shaped or ring like structures. They most often appear as short rods along the periphery of red blood cells. Whole blood that has not been in contact with an anticoagulant is preferred for examination as the organism detaches from the clls when in anticoagulant. In cats, Howell Jolly Bodies, polychromasia, nucleated red blood cells and anisocytosis are almost always seen. Transmission of the parasite is thought to occur by blood sucking arthropods, such as fleas, or by bite wounds. Queens can transmit the parasite to their offspring, although it is unknown if the transmission occurs transplacentally, at birth, or trans mammary. A cat infected with H Felis may show mild anemia without clinical signs or may show severe anemia with marked depression, or death. There may be a decrease in the packed cell volume. The life of the erythrocyte shortens and the primary method of cell destruction is immune mediated.
Haemobartonella canis is rare in dogs and is usually only seen in slenectomized or immunosuppressed dogs.
Microfilaria is not a parasite that infects blood cells, but it can be found in the blood stream. Immature heartworms, called microfilaria, circulate in the blood stream before migrating to the heart and lungs to reproduce.