Thrombocytopenia in Dogs
Dr. Leah Cohn
Specific diagnostic tests will be needed for your veterinarian to diagnose thrombocytopenia, determine its underlying cause and determine the effects of thrombocytopenia. Tests may include: A complete medical history and physical examination. You should be prepared to provide a complete history about your dog. Important questions will be asked about your dog's home environment including time spent outdoors, travel history, previous illnesses, recent vaccinations, medications (e.g. aspirin, antibiotics) and any symptoms you have noticed. Factors such as your dog's age, breed and gender will influence the types of diseases your veterinarian will consider as possible causes of thrombocytopenia.
Mild to moderate thrombocytopenia usually does not cause spontaneous bleeding and causes no abnormalities on physical examination. Severe thrombocytopenia, however, often causes characteristic abnormalities on physical examination. These abnormal findings include tiny pinpoint hemorrhages on the gums, whites of the eyes (sclera) or skin called petechiae, and skin bruising called ecchymosis. Bleeding into body cavities or joints is not common in animals with thrombocytopenia. Your veterinarian also may examine the backs of your dog's eyes (retinas) for evidence of bleeding with an instrument called an ophthalmoscope.
A complete blood count (CBC or hemogram) including a blood platelet concentration to determine if your dog has thrombocytopenia and to evaluate for anemia that may have resulted from blood loss
Serum biochemistry tests to evaluate other organ systems and to determine the general health of your dog
Urinalysis to evaluate for blood in the urine (hematuria), infection, or protein in the urine that may occur with some diseases that cause thrombocytopenia
Unfortunately, a highly reliable diagnostic test is not available for one of the most common causes of severe thrombocytopenia in dogs called immune-mediated thrombocytopenia or idiopathic thrombocytopenic purpura (ITP). Immune-mediated diseases result when the body's immune system fails to recognize its own cells and tissues and begins to attack them as if they were foreign invaders. In immune-mediated thrombocytopenia, the immune system attacks and destroys platelets. Due to lack of a reliable and specific diagnostic test for this disease, immune-mediated thrombocytopenia usually is diagnosed by ruling out other known causes of thrombocytopenia.
Additional diagnostic tests may be recommended on a case-by-case basis to determine the cause of thrombocytopenia and to insure that your dog receives optimal medical care. Examples of additional tests may include the following:
Tests of the immune system. Systemic lupus erythematosus (SLE) is a generalized autoimmune disease that can cause damage to many tissues such as kidneys, joints, and skin and can result in destruction of platelets. The LE cell preparation and anti-nuclear antibody (ANA) test are two tests that may be requested if your veterinarian suspects your dog may have systemic lupus erythematosus. Immune-mediated destruction of platelets alone is more common than systemic lupus erythematosus.
Tests for specific infectious diseases. Results of the medical history, physical examination and other blood tests often determine whether or not specific tests for infectious diseases are necessary. Some infectious diseases that may be considered include tick-borne diseases such as Rocky Mountain spotted fever and ehrlichiosis. Other infectious diseases can cause blood platelet concentrations to decrease, but most of these other diseases cause only mild thrombocytopenia.
X-rays of the chest or abdomen to evaluate dogs with thrombocytopenia. Enlargement of the spleen often is observed in dogs with immune-mediated thrombocytopenia or infectious causes of thrombocytopenia since the spleen is a common site of platelet destruction. Enlargement of the spleen often can be identified on X-rays of the abdomen.
Abdominal ultrasound examination if your veterinarian suspects a tumor or enlargement of abdominal organs. After clipping the hair and applying a gel to facilitate transmission of ultrasound waves, a probe is held against the abdomen and ultrasound waves create images of the abdominal organs. This same technology is often used in pregnant women to visualize the fetus. If abdominal ultrasound is necessary, your veterinarian may refer your dog to a veterinary radiologist or internist for evaluation.
If a mass or enlarged organ is identified, a biopsy may be recommended to identify the nature of the mass or enlargement. A biopsy specimen may be obtained by surgery or using a specialized biopsy needle inserted through the body wall under ultrasound guidance.
If your veterinarian is concerned that your dog's bone marrow is not producing adequate numbers of platelets, a biopsy or needle aspirate of the bone marrow may be performed. This procedure is performed using a local anesthetic to numb the biopsy site after the animal is sedated.
Other tests of clotting ability may be recommended. Common clotting function tests include prothrombin time and activated partial thromboplastin time, which evaluate two clotting pathways in the body.