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Veterinary & Aquatic Services Department, Drs. Foster & Smith
Immune and Blood System
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Thrombocytopenia is a disorder in which platelet numbers are lower than normal. Platelets are actually fragments of special cells that are necessary for proper clotting of blood. When a blood vessel is cut or breaks, the platelets gather around the site and stick to each other forming a plug. During normal activity, small blood vessels commonly have microscopic breaks which are plugged with platelets. When platelet levels are low, these plugs do not form and we can see various types of bleeding.

What causes thrombocytopenia?

Thrombocytopenia can occur because of four processes:

  • Decreased production of platelets by the bone marrow
  • Increased use of platelets through blood clotting
  • Destruction of platelets by the immune system
  • Removal of platelets from the general circulation (sequestration)

Diseases associated with these four processes are shown in Table 1.

Decreased Production Increased use Destruction Sequestration
  • Estrogen medications
  • Certain other medications such as chloramphenical
  • Chemotherapy or radiation therapy
  • Estrus
  • Bone marrow diseases, eg., aplastic anemia, some leukemias
  • Ehrlichiosis
  • Disseminated intravascular coagulation (DIC)
  • Endotoxic shock
  • Vasculitis
  • Hemangiosarcoma (a cancer)
  • Primary immune-mediated (autoimmune) thrombocytopenia
  • Other autoimmune diseases such as lupus
  • Infections such as ehrlichiosis, babesiosis, and heartworm
  • Certain medications such as sulfas or possibly vaccines
  • Certain toxins
  • Splenic torsion
  • Splenomegaly (enlarged spleen)
  • What are the signs of thrombocytopenia in a dog?

    A dog with thrombocytopenia may or may not show signs of bleeding, depending upon how low the platelet numbers are. Signs of thrombocytopenia include:

    • Lethargy
    • Loss of appetite
    • Weakness
    • Small pinpoint hemorrhages called 'petechiae', commonly found on the mucous membranes such as the inside of the mouth.
    • Larger hemorrhages under the skin, especially on the ventral abdomen (belly) and groin area
    • Bleeding from the mucous membranes including the gums
    • Nosebleeds
    • Pale mucous membranes
    • Bleeding from the gastrointestinal tract that may appear as black, tarry stools or stools with fresh blood in them
    • Blood in the urine
    • Hemorrhages in the eye
    • Prolonged bleeding after an injury or surgery

    How is thrombocytopenia diagnosed?

    A complete history would be obtained to try to identify possible causes of the bleeding tendencies and gather information on when they started, etc. A thorough physical exam would be conducted and the veterinarian would look for signs of other diseases that may be a cause of the thrombocytopenia.

    Any dog showing signs of a bleeding problem would have a complete blood count (CBC) and a platelet count performed. A platelet count is a special test done on a blood sample that measures how many platelets are present in a specific quantity of blood. A coagulation profile, which tests for the normal presence of clotting factors in the blood, would also be performed.

    It is essential to identify the cause of the thrombocytopenia, since different causes are treated differently. Therefore, a veterinarian may recommend a dog with thrombocytopenia be tested for heartworm, ehrlichiosis, and other infectious causes. Tests such as a urinalysis and chemistry panel would help to assess the health of other organs. Radiographs may be advised to look for cancers or other diseases that could cause thrombocytopenia. A bone marrow aspirate may also be performed.

    How is thrombocytopenia treated?

    The treatment of thrombocytopenia depends on the cause and the severity of the condition. If the platelet levels are very low, it can be a life-threatening condition and blood transfusions may be necessary. In cases of infections, antibiotics would be prescribed. Immune-mediated thrombocytopenia is generally treated with corticosteroids and possibly other immunosuppressing drugs. Cancers would be treated based on the type of cancer and location.

    What is the prognosis for dogs with thrombocytopenia?

    The prognosis depends on the cause and the severity of the condition. Relapses with immune-mediated thrombocytopenia are relatively common.

    What should I do if I think my dog may have thrombocytopenia?

    Thrombocytopenia can be life-threatening. If you think your dog may have a bleeding problem, contact your veterinarian immediately.

    References and Further Reading

    Heseltine,J; Carr, A. Overcoming the diagnostic and therapeutic challenges of canine immune-mediated thrombocytopenia. Veterinary Medicine 2007;August:527-538.

    Brooks, MB; Catalfamo,JL. Platelet disorders and von Willebrand Disease. In Ettinger, SJ; Feldman, EC (eds.) Textbook of Veterinary Internal Medicine, Sixth Edition. Elsevier, St. Louis MO; 2005; 1918-1929.

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