Top 5 Red Blood Cell Pathologies
Article By: Pierre Hebert DMV, IPSAV, DACVP, Biovet Laboratories
Hematology is an important tool of the diagnostic procedure in small animal medicine. It can be used in preventative ways before surgery or when the practitioner is trying to determine the cause of clinical signs exhibited by a sick patient. Results from in house analyzers are quick and accurate. It allows the veterinarian to act promptly and accurately. Blood smear microscopic examination are an underutilized complement to the results provided by the hematology analyzer. Blood smear microscopic examinations can help pinpoint the causes of hematologic abnormalities. It can also provide tips on underlying metabolic diseases undetectable by hematology alone. A manual blood smear can be done easily and quickly and is worth the investment in time to provide additional detail when required. To help improve hematology diagnostic accuracy, I would like to provide you with the top five of the most frequent red blood cell pathologies and their significance.
Echinocytes, or crenated erythrocytes, are spiculated erythrocytes (figure 1). The surface projections are numerous, evenly distributed and of similar size. It is mostly considered an artifact secondary to slow drying of the blood smear or as a result of prolonged sample storage before slide preparation. This has also been related to snake envenomation, underlying neoplasia (such as lymphoma and mast cell tumor) and glomerulonephritis. This is by far the most common RBC pathology observed on microscopic examination. Most of the time, this is a non-significant finding.
Acanthocytes, or spur cells, are erythrocytes covered by irregularly shaped unevenly distributed surface projections (figure 2). This erythrocyte anomaly results from alteration in cholesterol or phospholipid concentration in the red blood cell membrane. This can be associated with liver disease in companion animals, and is a common finding in cats suffering from hepatic lipidosis. This has also been related to erythrocytes fragmentation secondary to disseminated intravascular coagulation, hemangiosarcoma, and glomerulonephritis.
Schistocytes are erythrocytes fragments (figure 3). They result from shearing of the erythrocytes secondary to intravascular trauma. These cells are mainly noted in dogs and are associated with disseminated intravascular coagulation, hemangiosarcoma, glomerulonephritis, hemophagocytic histiocytic disorders, dirofilariasis, and iron-deficiency anemia. In case of hemangiosarcoma in dogs, it is not unusual to notice the presence of acanthocytes as well. Fragmentation in iron-deficiency anemia could be secondary to oxidative injury to the red blood cell membrane. In anemic dogs, the presence of these cells prompts further investigation related to underlying neoplasia including imaging of the abdominal and/or thoracic cavity. In cats, these cells are not exhibited as much and most of the time they will be associated to marked poikilocytosis, secondary to hepatic.
Spherocytes are deep red staining, spherical cells that lack central pallor (figure 4). These cells result from loss of cell membrane secondary to partial phagocytosis by macrophages. This is secondary to the presence of antibodies or complement on the surface of red blood cells. Spherocytes are related to immune mediated hemolytic anemia. Is such case, it is not unusual to observe microscopic agglutination as well. Spherocytes are also reported after blood transfusions, snake envenomation, bee stings, and zinc toxicity. Because of the small size of cat red blood cells and the lack of central pallor, spherocytes are difficult to detect in this species.
Codocytes, or target cells, are cells with a bull’s-eye appearance on blood film (figure 5). These result from increased red blood cell membrane cholesterol to phospholipid ratio. Although these cells are a common and mostly non-significant finding, they can be related to liver disease. The presence of a large numbers of such cells should prompt a liver enzyme panel.
Poikilocytosis is a general term for “abnormally shaped erythrocytes”. Its significance is mostly related to the presence of multiple red blood cell pathologies simultaneously (figure 6). The most frequent simultaneous anomalies noted are acanthocytes, schistocytes, and echinocytes. Poikilocytosis can be related to liver disease (hepatic lipidosis in cats), disseminated intravascular coagulation, glomerulonephritis and hemangiosarcoma in dogs.
The aforementioned anomalies are the most frequent red blood cell pathologies noted in companion animals. Although the observation of abnormal red blood cells is not always an absolute indication of an underlying pathologic process, it can sure help in case of abnormal results provided by the hematology analyzer.