Thrombocytopenia (Low Blood Platelets) in Dogs

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In-depth Information on Canine Thrombocytopenia 

Thrombocytopenia does not always lead to excessive bleeding. Normally, there are more than 600,000 platelets per microliter of blood, which is about one millionth of a quart. Platelet numbers in blood must fall to about 10,000 to 40,000 per microliter before spontaneous bleeding becomes likely. Moderate thrombocytopenia may be found in animals with no evidence of bleeding and this finding often serves as a clue to an important underlying disease process.

Thrombocytopathia is a term that refers to abnormal function of platelets. Animals with thrombocytopathia have adequate numbers of platelets in their blood, but the platelets do not function properly. Thrombocytopathia may be inherited or acquired. Acquired defects in platelet function may be due to drugs (such as aspirin), cancer, or organ failure (such as kidney failure, liver failure).

Coagulation refers to the clotting ability of blood, and normal coagulation arises from the combined effects of properly functioning platelets, blood vessel lining cells (endothelium) and protein clotting factors found in the blood and tissues. Deficiency or abnormal function of any of these components can cause spontaneous bleeding. Occasionally, a disease causes defects in more than one of these components simultaneously.

The following disease processes may cause symptoms similar to those seen in dogs with severe thrombocytopenia:

  • Vasculitis. This inflammatory disease of blood vessels is characterized by tiny defects in the lining that can allow blood to leak from the vessels. Platelets are attracted to these defects and attempt to plug the holes. Consequently, vasculitis often also results in thrombocytopenia. Several different disease processes can cause vasculitis, including some types of infection and abnormal immune system function that results in an attack against the vessel walls.
  • Von Willebrand’s disease. The is an inherited defect in a body protein that normally facilitates the attachment of platelets to each other and to damaged vessel walls. Animals with this disorder have prolonged bleeding times and sometimes experience excessive bleeding after minor injury or surgical procedures. It is an inherited trait in several breeds of dogs, notably Doberman pinschers.
  • Insufficient quantities of coagulation proteins. Inherited deficiency of a coagulation protein is known as hemophilia. Certain disease processes such as liver failure can result in acquired deficiency of coagulation proteins.
  • Warfarin. Ingestion of this compound, a common ingredient in rat poisons, can result in a life-threatening bleeding disorder. Some of the currently available rat poisons contain ingredients that have the same effect as warfarin but are much more potent and longer acting. These poisons affect vitamin K metabolism such that coagulation proteins cannot be properly activated.
  • Disseminated intravascular coagulation (DIC). This refers to life-threatening bodywide coagulation that occurs as a complication of several serious diseases including infections and cancer. During development of DIC, tiny clots form throughout the body in small blood vessels. Both platelets and coagulation proteins are consumed in the formation of these small clots. Widespread life-threatening bleeding occurs when the body’s platelets and coagulation proteins become depleted.
  • Disease in specific organs or body locations. Diseases can cause bleeding that is localized to those areas. For example, bladder stones can cause blood in the urine, nasal tumors can cause bleeding from the nostrils (often primarily on one side), gum disease can cause bleeding around the teeth, and trauma can cause bruising or bleeding.
  • Skin rashes can be mistaken for the tiny pinpoint hemorrhages called petechiae that are found in animals with severe thrombocytopenia. When finger pressure is placed on the red spots in a rash, the redness typically blanches out whereas with petechiae, the redness stays.
  • In-depth Information on Diagnosis of Canine Thrombocytopenia 

    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.
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