All about anemia
Anemia is the result of an underlying disease process. It is defined as a reduction in the number of circulating red blood cells, below normal hematocrit and hemoglobin levels, resulting in decreased oxygen capacity. Once anemia is presented, the veterinarian must find the underlying cause or causes, and then apply the appropriate treatment plan. The technician plays an important role in care of anemic patients; understanding blood smears and documenting daily RBC morphology and platelet estimates, and reporting the pet’s progress to the doctor on a daily basis, is very beneficial.
Anemia is routinely classified as either regenerative or nonregenerative, and either acute or chronic. In regenerative anemia, the bone marrow responds adequately to the decreased red cell population by increasing red blood cell production and releasing reticulocytes. Regenerative anemia is commonly caused by either hemorrhage or hemolysis. With nonregenerative anemia, the bone marrow does not respond to the decreased number of circulating red blood cells. There are many disease processes that can cause nonregenerative anemia, including kidney disease and neoplasia.
Regenerative anemia
Regenerative anemia can be either acute or chronic. A pet can suffer from acute hemorrhagic anemia due to a traumatic injury that results in blood loss. Immediately following an acute, nonfatal hemorrhage in a healthy animal, the packed cell volume results may be unchanged; this is due to the blood quality being normal, just decreased in total volume. A few hours following the event the body will shift fluid into the vasculature to restore blood volume, causing a drop in packed cell volume and hemoglobin, which will give us the pet’s true hematocrit level. With a small non-life threatening hemorrhagic anemia, the pet will begin to release stored erythrocytes from the spleen and bone marrow. This may be enough to restore the packed cell volume. In addition, the lower oxygen levels will stimulate the kidneys to release erythropoietin to the bone marrow. In some of these cases the pet may not need a transfusion, or only need a single transfusion until the response from the bone marrow is complete. If the volume of acute blood loss is greater than one third of total blood volume, the pet may present with severe shock, including pale mucous membranes, hypotension, and tachycardia. In these cases many pets will need immediate, and possibly multiple blood transfusions, to support them until their bodies can begin correcting the anemia.
With chronic hemorrhagic anemia, the pet may have a slow steady blood loss, as with a gastric ulcer or a heavy hookworm infestation. Even severe flea or tick burdens can cause a pet to be anemic. Over-use of a blood donor can also result in a chronic hemorrhagic anemia. When the cause has been discovered and the hemorrhagic anemia has been controlled, resolution can take 1-2 weeks.
In hemolytic anemia, the body begins to destroy is own red blood cells, resulting in hemolysis. These pets will present with icterus, which is not seen in hemorrhagic anemia. Hemoglobin is the erythrocyte protein that transports oxygen. When hemolysis occurs bilirubin is released, giving the pet a yellowish colour. The serum or plasma in these pets will also be yellow or orange. The most commonly seen form is immune-mediated hemolytic anemia.
Heinz body anemia in dogs can occur due to zinc toxicity, garlic or onion ingestion, and acetaminophen. Many people do not realize that zinc is the main metal component of pennies, not copper, therefore a pet showing a Heinz body anemia should always be evaluated for penny ingestion. Erythrocytes with Heinz bodies are more fragile than normal erythrocytes, causing them to be lysed in the spleen. When stained with new methylene blue stain, Heinz bodies can be visualized as pale blue structures protruding off the erythrocyte. The diagnosis of Heinz body anemia is based on the findings of regenerative anemia, evidence of hemolysis, presentation of Heinz bodies on the erythrocytes, and a history of exposure to one or more indicators. In cats, Heinz bodies can be a normal occurrence.
Other types of hemolytic anemia are alloimmune transfusion reactions, which occur when the pet has a reaction to a blood transfusion. Cats can become infected with one or more Mycoplasma species, which will result in the destruction of red blood cells. Clinical signs include fever, lethargy, and anorexia. Envenomation has been known to cause hemolytic anemia in dogs following the bite of the brown recluse spider, rattlesnakes, and even bee stings.
Non-regenerative anemia
Nonregenerative anemia can be grouped into two broad categories: maturation defect anemias and hypoproliferative anemia; in most cases bone marrow evaluation is required to get a definitive diagnosis. The most common forms of maturation defect anemia are feline leukemia in cats, and iron deficiency anemia in dogs. Iron deficiency anemia is the end stage of chronic blood loss. With nonregenerative anemia, the bone marrow production of erythrocytes is stopped or severely decreased, and is not able to meet the needs of the pet. Nonregenerative anemias may be the result of nutrient deficiencies, especially iron, protein, and B vitamins. Nutrient deficiencies can also be seen with malabsorption syndromes and chronic blood loss; both can deplete the store of iron. Nonregenerative anemia may also be caused by bone marrow failure. Primary bone marrow failure is called aplastic anemia, which indicates a total failure of any type of production. The prognosis for aplastic anemia is unfortunately almost always terminal. Secondary bone marrow failure is usually caused by a lack of response to the anemia by the bone marrow. This routinely involves the lack of erythropoietin production by the kidneys. In addition to evaluating a blood film, most suspected nonregenerative anemia patients will have a bone marrow biopsy and/or bone marrow cytology performed to confirm a diagnosis.
The blood film in the nonregenerative anemia patient will have minimal or no signs of regeneration. Red blood cells will be normocytic and normochromic, and very few nucleated red blood cells or polychromatic cells will be noted.
Pets with chronic nonregenerative anemia can seem healthier than they actually are, especially cats. The symptoms of acute anemia are often not presented, and the chronically anemic pet may only seem lethargic, have some weight loss, and look pale. On closer evaluation these patients will have a severely low packed cell volume that may seem not compatible with life. The chronic kidney failure cat can come into the office looking thin but perky, only to find his hematocrit is 11%. In the acutely anemic patient we can see tachycardia and increased pulses, but in the chronic patient the heart rate and pulse become more normal. These patients are more prone to cardiomegaly and multifocal retinal bleeding.
Blood film evaluation in anemic pets
Properly evaluating blood films on our anemic patients is vital to their treatment. Often the veterinary lab technician will be the first person to review the daily blood films. The case doctor may be looking for causes of the anemia, and signs of regeneration.
Red blood cell morphology
Description |
Definition |
Microcytic |
Smaller than average RBC |
Macrocytic |
Larger than average RBC |
Hypochromia |
Pale colour, lacking central pallor |
Polychromasia |
Immature RBC with RNA present. Larger, blue in colour |
Anisocytosis |
Variation in size of RBC |
Poikilocytosis |
Variation in shape of RBC |
Spherocyte |
Small dense RBC, no central pallor. Diagnostic of IMHA |
Target cell (codocyte) |
Resembles a bull’s eye |
Burr cell (echinocyte) |
Also known as crenation; artifact |
Acanthocyte |
Bulbous rounded uneven projections. Can indicate liver disease |
Leptocyte |
Thin, almost colourless |
Schistocyte |
RBC fragment. Indicates DIC or neoplasia |
Heinz body |
Small rounded areas of denatured hemoglobin |
Howell-Jolly Body (HJB) |
Nuclear remnant. Small single dark stained circle |
Nucleated red blood cell (nRBC) |
Immature RBC, can resemble lymphocytes |
Susan Kolkka, AAS, LVT, VTS (Clinical Pathology) received her Associates in Applied Sciences degree from SUNY Delhi in Delhi, NY in 1988, and has a New York State license in Veterinary technology. She began working for the Oradell Animal Hospital immediately after graduating. Oradell Animal Hospital is one of the largest private animal hospitals on the East Coast. She has held several positions there, including Laboratory Supervisor, Blood Bank Coordinator, and Clinic Manager. She is a skilled phlebotomist and trains all support staff in phlebotomy.
Susan recently won the NAVTA sponsored Case Report Presentation Contest at the North American Veterinary Conference in 2015. She is a Charter Member of the Association of Veterinary Clinical Pathology Technicians (AVCPT).
This article is based on Ms. Kolkka’s presentation at the North American Veterinary Community Conference in Orlando, FL.CVT
