Veterinarians recommend annual exams that include a blood count and chemistry profile.
Reprinted with permission from Dog Watch, January 2008
The chief function of canine blood, like human blood, is to transport oxygen and nutrients to the body's tissues and to carry carbon dioxide and various waste materials away from them. But this is by no means the only vital role that this rich, red fluid plays. Typically accounting for about seven percent of a dog's body weight, the blood is a key contributor to many other processes, such as cell development, tissue repair and the warding-off of infection
The constituents of a dog's blood are comparable to those of human blood. They include red cells (erythrocytes), which are critical for oxygen transport and also assist in the removal of toxic carbon dioxide; white cells (leukocytes), which help protect an animal against infection and desease; platelets, which promote clotting when it's needed; and a colorless fluid (plasma) in which these and other life-supporting blood components -such as hormones, proteins and salts - are suspended.
Most Frequently Seen
Disorders directly associated with blood abnormalities or anomalies may not be as easily recognized by owners as many other canine diseases. But that by no means suggests that dogs are not susceptible to blood disorders. On the contrary, says Marjory Brooks, DVM, associate director of the Comparative Coagulation Laboratory at Cornell University's College of Veterinary Medicine. At the Cornell University Hospital for Animals (CUHA), she notes, "We see them every day - low platelet counts, low red-cell counts, high white-cell counts, clotting problems, blood-related cancers, even poisonings."
Among the categories of canine blood disorders, says Dr. Brooks, the most frequently occurring is anemia, a condition resulting in inadequate circulation of oxygen. While not a disease in itself, anemia is one sign of several pathologic processes.
There are two forms of this disorder. In regenerative anemia, the red blood cells are reduced in number as a result of acute or chronic bleeding or tissue destruction. In some cases - with a deep wound, for example -the blood loss will be obvious. In other cases - those involving gastrointestinal bleeding, for example, or infection with blood-sucking parasites - the signs of blood loss may be subtle and may go unnoticed for an extended period.
In nonregenerative anemia, the bone marrow fails to produce new red cells rapidly enough to replace old cells that have been destroyed or have otherwise become dysfunctional. Common influences include infection with a tick-borne disease (such as ehrlichiosis) or chronic kidney failure, which severely suppress bone marrow function, and cancer of the bone marrow, in which the presence of malignant neoplasms overwhelms normal cell-producing tissue and renders it nonfunctional.
Other canine blood disorders that are seen with relative frequency at CUHA, says Dr. Brooks, include:
- Acute and chronic leukemias, cancers of the blood marked chiefly by a significant and in some cases rampant - increase in the number of white blood cells in circulation or in the bone marrow. If untreated, these diseases can lead to fatal bone marrow failure and loss of organ function throughout a dog's body.
- Von Willebrand's disease, a bleeding disorder marked by a lack of a certain protein that enables platelets to adhere to the lining of a damaged blood vessel. This results in the blood's inability to clot as needed. Dogs with this disorder may experience frequent nosebleeds and may have blood in their stools. Without transfusion, a dog with von Willebrand's disease may succumb to shock and blood loss after a traumatic injury.
- Thrombocytopenia, or low platelet count, which arises from infection, drug reaction, cancer and other causes. Severe thrombocytopenia often develops in dogs as an autoimmune process, in which the immune system loses self-tolerance and destroys platelets as if they were foreign invaders. This disorder typically manifests itself in bleeding gums, "pinpoint" skin hemorrhaging, spontaneous bruising and excessive bleeding from superficial wounds.
- Anticoagulant rodenticide toxicity, which causes severe bleeding after ingestion of warfarin-type poisons designed to kill rats and mice. A dog that has swallowed a rodenticide develops a bleeding tendency over the course of one or two days. Hemorrhage may be external, with obvious blood loss from the nose or mouth or in the urine or stool. Internal bleeding may go unnoticed, progressing to more severe signs of shock and respiratory distress. Without appropriate therapy, anticoagulant rodenticide poisonings are often fatal.
- Some canine blood disorders have a genetic component; they can be passed down from generation to generation. For example, Dr. Brooks points out that Doberman pinschers have a comparatively high incidence of von Willebrand's disease, while hereditary anemias have often been identified in springer spaniels and basenjis.
Early identification of any canine blood-associated disorder will prompt appropriate treatment, which is likely to reduce its impact on an animal's general health and may indeed save its life. Toward this end, veterinarians, including Dr. Brooks, generally recommend that a thorough medical evaluation include two blood tests a complete blood count (CBC) and a blood-chemistry panel. Testing is especially valuable at or past the age of six, when dogs are approaching or are well into their geriatric years and are naturally at increased risk for age-related disease.
The tests are inexpensive, and they require only that the dog sit quietly for a moment while the veterinarian or technician draws a small amount of blood. Moreover, these tests are speedy. In most cases, the results of routine bloodwork can be available almost immediately.
Additional tests are occasionally required, however, when the results of a basic test are confusing or not readily explicable; in such cases, blood samples may have to be shipped to a specialized lab. If a specific blood test confirms the suspicions raised by the CBC or chemistry panel results, further diagnostic efforts may focus on a diseased organ, with imaging technology such as ultrasound, or may involve collection of bone marrow samples for direct examination by a pathologist.