Thrombocytopenia in Dogs

By Krista Williams, BSc, DVM, CCRP; Ernest Ward, DVM; Updated by Amy Panning, DVM

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What is thrombocytopenia?

Thrombocytopenia is a decrease in the number of blood platelets, also known as thrombocytes, circulating in the blood.

What are platelets?

Platelets are produced in the bone marrow and circulate in the blood. They clump together to seal broken or leaking blood vessels to prevent blood loss. They are an important factor in the blood clotting mechanism, and thrombocytopenia can lead to spontaneous bleeding or bruising.

What causes thrombocytopenia?

Severe or prolonged blood loss, increased internal destruction of platelets, or impaired bone marrow production can lead to a short-term (acute) or long-term (chronic) deficiency of platelets.

Are any diseases or conditions associated with thrombocytopenia?

Many severe diseases have thrombocytopenia as one component of the condition, including:

  • infectious diseases such as parvovirus, canine infectious hepatitis virus, canine distemper, leptospirosis, many tick-borne diseases (e.g., Lyme disease), salmonella, and heartworm disease 
  • immune-mediated diseases (e.g., immune-mediated thrombocytopenia)
  • cancers (e.g., lymphoma, hemangiosarcoma) 
  • medications including estrogen, phenylbutazone (Butazolidin®, Butatron®), phenobarbital (Luminal®, Barbita®), fenbendazole (Panacur®), cephalosporin antibiotics, sulfa antibiotics, ACE inhibitors, and several chemotherapy medications 
  • toxins and venoms (e.g., zinc, xylitol, snake bites)

Is thrombocytopenia common in dogs?

Thrombocytopenia is quite common. Some surveys have shown as many as 5% of all dogs admitted to veterinary hospitals have a low platelet count.

"Some surveys have shown as many as 5% of all dogs admitted to veterinary hospitals have a low platelet count."

What are the clinical signs of thrombocytopenia?

Severe thrombocytopenia may cause abnormal bleeding that shows up as petechiae (small red spots on the skin or gums), ecchymoses (larger bruises), bloody urine, vomit, or stool, and melena (tar-colored stool). The blood loss can cause anemia (low red blood cell count), resulting in pale gums, increased breathing rate, and weakness. Many dogs with thrombocytopenia will not show any obvious signs, which is why blood testing is so important.

How is thrombocytopenia diagnosed?

This condition is easily diagnosed with a blood test. Platelet counts are often performed in conjunction with a complete blood cell count (CBC). Platelet counts of less than 20,000 to 30,000 per microliter of blood (normal platelet counts are 175,000 - 500,000) make spontaneous hemorrhage likely.

Additional diagnostic tests are used to investigate the underlying causes of the problem. Depending on the nature of the suspected underlying process, these may include additional blood tests, radiographs (X-rays), ultrasound, or bone marrow sample tests.

How is thrombocytopenia treated?

If blood loss is acute or sudden, a blood transfusion may be required to stabilize the patient. Platelet-rich plasma may also be used to temporarily increase platelet numbers to reduce spontaneous hemorrhage. Other treatments will be needed to treat the specific underlying cause of the thrombocytopenia to minimize or prevent a recurrence.

"If blood loss is acute or sudden, a blood transfusion may be required to stabilize the patient."

Can there be bleeding disorders with normal numbers of platelets?

Yes, if platelet function is impaired. This can be a side effect of certain medications, including some antibiotics. There are inherited platelet defects, such as Von Willebrand's Disease (see handout “Von Willebrand’s Disease in Dogs” for more information), that are common in certain breeds of dogs, especially Doberman Pinschers. Congenital platelet defects also occur in Otterhounds, Great Pyrenees, American Cocker Spaniels, and Basset Hounds. Diagnosis requires tests of platelet function. There are no specific treatments other than blood transfusions as needed.

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