One of most common and obvious causes of bleeding (hemorrhage) is trauma. In most instances the bleeding will be self-limiting (stop on its own) unless the wound is severe. Occasionally bleeding may occur from sites such as the nose, mucous membranes, or urinary tract, but no incidence of trauma has occurred. Or perhaps ‘pin point’ hemorrhages are found on the gums or skin (these are called petechiae). These more troublesome clinical signs may be associated with problems related to blood coagulation factors, platelets, platelet function, or some other underlying disease.
How do we determine the cause of bleeding in my pet?
First, a thorough history, including a list of all medications that your pet is receiving, is taken, and a complete physical examination is performed.
The nature of the hemorrhages will often provide us with clues as to their cause. Some breeds of dogs are more likely to suffer from certain blood clotting disorders.
Next, one or more screening tests, which may include a CBC (complete blood count), serum biochemistry profile, urinalysis, coagulation profile, buccal mucosal bleeding time (BMBT) and/or von Willebrand’s factor assay, will be recommended.
What might these screening tests indicate?
A CBC (complete blood count) provides an evaluation of the red blood cell, the white blood cell, and the platelet components of a blood sample. A hematology analyzer will provide us with the total numbers of these cells, and evaluation of a blood smear will allow us to look at the physical characteristics of these cells.
Because effective blood clotting requires both clotting (coagulation) factors and adequate numbers of normally functioning platelets, evaluation of the platelet numbers is an important component of the CBC. Bleeding may occur if platelet numbers are markedly reduced: this reduction is called thrombocytopenia. The causes of thrombocytopenia are many and include immune-mediated destruction of platelets, decreased production of platelets, or increased consumption of platelets.
Other features of the CBC may help us decide upon the likely cause of the thrombocytopenia. For example, if the white blood cell numbers are markedly increased in conjunction with the thrombocytopenia, then severe inflammation or infection may be causing increased consumption of platelets. Or if there are abnormal or atypical cells in the blood, then perhaps an underlying bone marrow disorder is causing the thrombocytopenia.
A CBC will also give us an indication of the amount of blood that your pet has lost so that supportive measures such as blood transfusions can be undertaken if necessary.
The serum biochemistry profile and urinalysis provide us with an overall assessment of many organ systems including the liver and kidneys. Diseases of the kidneys and liver are known to affect the function of platelets as well as influencing the balance of clotting factors present in blood. Therefore it is important to be able to either confirm or rule out liver or kidney disease as a possible cause of abnormal bleeding.
A coagulation profile allows us to assess the functional activity of the proteins involved in blood clotting. The pattern of change in these clotting tests may allow us to determine what is causing the bleeding in your pet. For example, rodenticide (rat poison) toxicity will initially cause the coagulation test ‘prothrombin time’ to be prolonged. Normal coagulation test results will rule out the possibility of decreased clotting factors as a cause of your pet’s abnormal bleeding.
Von Willebrand’s factor is a protein that assists in the adherence or ‘stickiness’ of platelets to sites of blood vessel injury and stabilizes one of the other coagulation factors in circulation. A deficiency in this factor can make an individual animal prone to bleeding episodes. Many breeds of dogs have hereditary deficiencies of von Willebrand’s factor, so it may be important to measure the amount of von Willebrand’s factor present in a blood sample and rule this common condition out as a cause of bleeding in your dog.
A buccal mucosal bleeding time (BMBT) is a test that evaluates the ability of platelets to form a platelet plug at the site of a small cut on the upper lip. A spring-loaded cassette is used to produce a small, precise cut, and the length of time required for bleeding to stop is measured. This time may be lengthened by a decreased platelet count or by decreased platelet function. Therefore the BMBT is usually reserved for patients that have normal platelet numbers but have questionable platelet function
The results of the above screening tests should provide a good indication of the underlying cause of bleeding in your pet. Depending on these test findings, it may or may not be necessary to conduct further tests.
What additional tests might be indicated?
Any additional testing will be entirely dependent upon the combined results of the physical examination, history, and screening tests.
If a bone marrow disorder is suspected, based upon the results of the CBC, then bone marrow collection and evaluation are indicated. A bone marrow evaluation is also sometimes used to confirm a tentative diagnosis of immune-mediated platelet destruction.
If underlying organ disease is suspected, for example of the liver, then further tests to evaluate liver function may be undertaken. Such testing may include serum bile acids, imaging studies of the liver (ultra-sound, x-rays) and biopsies.
If infectious disease is thought to play a role, then blood tests for the presence of infectious agents such as heartworm or Ehrlichia in dogs, and feline leukemia virus or feline immunodeficiency virus in cats, may be undertaken.
Thrombopathias (disorders of platelet function rather than problems related to decreased platelet numbers) are more difficult to diagnose. A process of elimination is used to diagnose these disorders – the more common causes of bleeding are ruled out by using the previously mentioned screening tests and any possible drug-related effects are ruled out by a careful history. Inherited thrombopathias are known to occur in certain breeds of dogs. Specific tests of platelet function are available only in specialized veterinary research facilities.