Bleeding Disorders in Dogs
Dr. Leah Cohn
Bleeding disorders can be either relatively minor problems or rapidly life threatening. The severity of the problem depends on both the amount of bleeding, and on the site of bleeding. Vasculitis. Vasculitis is an inflammation of the blood vessels. The vessels become damaged, and small holes in the vessels allow for tiny amounts of blood to leak from the vessel. This is often seen as pinpoint sized red spots (petechiae) on the gums or the whites of the eyes. Vasculitis may be caused by a variety of infectious diseases or by immune mediated disease where the body's own immune system begins to attack the body instead of attacking germs.
Bleeding may be obvious, as is the case with open cuts or nose bleeds, or it may be harder to detect. Bleeding into the stomach or intestines, for example, may be visible as dark, tarry stool that an owner may not notice. Likewise, bleeding under the skin, or into body cavities including the joints, abdomen (belly), or chest may be difficult or impossible for the owner to identify.
Any time an animal exhibits bleeding either with no known provoking injury, or excessive or prolonged bleeding after a known injury, a diagnostic investigation is warranted.
Bleeding disorders can result from a variety of different processes, and each process can result from several different diseases. Coagulation is the sum of all the events that allow blood to clot and thereby stop bleeding. Normal coagulation first requires that the blood vessel lining, or endothelium, provide signals that it has been torn. Next, adequate numbers of platelets must fill in the hole in the torn blood vessel and must stick to both the vessel lining and to each other. Finally, soluble factors in the liquid part of the blood must be activated to form a solid, sticky substance known as fibrin in the area where the platelets have covered the hole. Problems in any of these processes, be it the proper functioning of the vessel wall, inadequate numbers or function of platelets, or insufficient soluble coagulation factors, can result in excessive bleeding. Some of the more common causes of disorders in these processes include:
Thrombocytopenia. Thrombocytopenia is a decreased number of blood platelets, the bloods cells that stick to and plug holes in the vessel. The body has a great reserve of platelets. As a result, only those diseases that cause a tremendous decrease in platelet numbers will result in excessive bleeding. The most common examples include an immune system attack directed against the platelets instead of germs, as well as a few specific types of infectious diseases. Because platelets are made in the bone marrow, infection, cancers, drugs or toxins that damage the bone marrow may also cause severe thrombocytopenia.
Thrombocytopathia. Thrombocytopathia is when the platelets don't function as they should. This can be due to drugs like aspirin, diseases like kidney failure or certain infections, or hereditary conditions. When there is a combination of thrombocytopenia and thrombocytopathy – decreased numbers of poorly functioning platelets – the resultant bleeding may be more severe than with either condition alone.
Von Willebrand's disease. This process is caused by deficiency of a substance that enables the platelets to stick to the vessel walls and to each other. This hereditary disease varies in severity from extremely mild to extremely severe. Often, the animal is diagnosed because of excessive bleeding at the time of either surgery or minor trauma.
Coagulation factor deficiency. There are a number of soluble coagulation factors in the liquid part of the blood or plasma. When properly activated, they proceed through a chain reaction to form a sticky substance known as fibrin. Fibrin serves to seal the platelets that have plugged the holes in a vessel into place until healing can occur. Several different diseases can be responsible for coagulation factor deficiencies. Hereditary coagulation factor deficiencies are known as hemophilia; the specific type of hemophilia reflects the specific factor that is missing. Because the liver is responsible for making most coagulation factors, liver failure can also result in deficiencies of coagulation factors.
Coagulation factor defects. Several of the soluble coagulation factors need to be kept in an active form to work properly. Substances such as warfarin and related compounds found in rat poison or certain prescription drugs can inhibit the vitamin K-dependent maintenance of soluble coagulation factors in an active state.
Disseminated intravascular coagulation (DIC). This syndrome is not a primary disease, but is the result of any one of several other severe diseases. In DIC, the blood becomes activated to clot when it should not. As a result, clots are formed throughout the body, and the body then works to break up the clots. In the process, both the factors necessary for proper clot formation, platelets and soluble coagulation factors, and the factors that break up the clot are used up, resulting in widespread bleeding.