Thrombocytopenia is a condition that affects certain cells in your dog's blood, and can occur for a variety of reasons. In thrombocytopenia, the platelet count is low. Platelets, also called thrombocytes, are the component of blood that clots together when there is an injury, thus stemming the bleeding. Thrombocytopenia decreases the ability of the blood to clot and can lead to spontaneous bruising or uncontrolled bleeding, although some dogs don't have any symptoms at all. There are many causes of thrombocytopenia, some more serious than others, and the condition can be mild to severe. Many dogs lead normal lives with treatment.

While any breed of dog, including mixed-breed dogs, can develop thrombocytopenia, it is more often hereditary in greyhounds and cavalier King Charles spaniels than other breeds, and the idiopathic form of thrombocytopenia is likeliest to strike small breeds or young-adult dogs.

What Is Thrombocytopenia?

Thrombocytopenia occurs when a dog has a low number of platelets in its blood. Platelets are important for blood clotting, so if your dog does not have enough of them, it is at risk of sudden bleeding or bruising. It is a fairly common disease in dogs, occurring in as much as 5 percent of dogs admitted to veterinary hospitals.

Symptoms of Thrombocytopenia in Dogs

If the thrombocytopenia is mild, you might not see any symptoms and only discover your dog has the condition during a routine veterinary checkup or a workup for another health problem. However, if the condition is advanced, you may see the following signs:

Since thrombocytopenia affects a dog's blood clotting abilities, spontaneous bleeding and hemorrhage can occur. This may happen with or without any trauma. Spontaneous bleeding in the eye shows as bloodshot or blood-streaked whites of the eye.

Nose bleeds may also suddenly occur, and sometimes blood can be seen in the stool and urine of a dog with thrombocytopenia. Black stool is an indication that the blood has been digested and is from higher up in the digestive system, but red blood in the stool may also be seen.

Finally, large bruises called ecchymoses along with small bruising called petechiae can occur on the gums and skin of a dog with thrombocytopenia. Although fur can cover bruises on much of a dog's body, you might notice bruises on the dog's belly or inner thighs where fur tends to be thinner. All of these symptoms are caused by having decreased clotting of blood due to insufficient platelets.

Causes of Thrombocytopenia

Thrombocytopenia can be caused by a number of diseases or issues in a dog:

Immune-mediated (ITP)

This is the most common cause of thrombocytopenia in dogs. ITP is an autoimmune disease, meaning that the immune system is attacking and destroying platelets. In primary ITP, also called idiopathic ITP, the cause is unknown. Small breeds and young-to-middle-aged dogs are likeliest to develop primary ITP. In secondary ITP, an underlying health problem, such as cancer or tick infection, triggers the autoimmune response.

Infections

Several diseases can cause thrombocytopenia, including canine distemper, parvovirus, ehrlichiosis, fungal infections, and bacterial infections.

Cancer

Some forms of cancer, including leukemia and multiple myeloma, can cause platelet destruction.

Genetics

Although the condition can strike any dog, certain dog breeds are more predisposed to thrombocytopenia. Cavalier King Charles spaniels and greyhounds are two of the breeds likeliest to inherit the condition.

Drug and Vaccine Reactions

Some medications, such as chemotherapeutics, certain antibiotics, and estrogen, can cause thrombocytopenia as a side effect.

Enlarged Spleen

Splenomegaly can result in thrombocytopenia since the spleen stores a large number of platelets.

Rodenticide Poisoning

If a dog accidentally eats some rodent poison that is designed to cause internal bleeding, thrombocytopenia may be seen alongside hemorrhage.

How Do Vets Diagnose Thrombocytopenia in Dogs?

In order to diagnose a dog with thrombocytopenia, a veterinarian will perform a complete blood count. This test shows how many platelets are present in the sample of blood. Typically, healthy dogs have platelet counts that are around 200,000/μL. Generally, when the number of platelets falls below 30,000/μL, symptoms of thrombocytopenia, such as bruising and nose bleeds, are seen.

Other tests may be performed to discover the cause of the thrombocytopenia, including blood tests to look for infections, signs of organ failure, cancer, or toxins. Occasionally, your vet may want to do more advanced tests, such as ultrasound, x-rays, or bone marrow biopsies, to check for other causes of the thrombocytopenia.

Treatment for Thrombocytopenia

The treatment for thrombocytopenia depends on the cause. Dogs with ITP generally require immunosuppressive drugs to keep their immune system from destroying platelets. Steroids, such as prednisone, are the most common drug used for this purpose. Most dogs will not have to remain on prednisone for life, but rather, can slowly taper down as their platelet counts rise to normal levels. This is important, because steroids have serious side effects, including weight gain, increased thirst and urination, and increased susceptibility to infections. You will need to work closely with your veterinarian during this time, and repeated blood tests will be required to check the dog's platelet levels.

Certain chemotherapy drugs temporarily increase the number of platelets, as do intravenous immunoglobulins. These are sometimes prescribed for rapid treatment of thrombocytopenia. If the dog has experienced serious blood loss, a transfusion might be required, as well.

If the thrombocytopenia is being caused by another condition, such as cancer or infection, then treatment of that condition should also help increase the dog's platelet count.

Prognosis for Dogs with Thrombocytopenia

Luckily, around 80 percent of dogs diagnosed with ITP will recover. However, relapse is common, so your dog will require lifelong observation and frequent veterinary checkups. If the thrombocytopenia is caused by another condition, such as cancer, infection, or a toxin, then the prognosis depends on how successfully that other condition can be treated.

How to Prevent Thrombocytopenia

Oftentimes, there is no way to prevent thrombocytopenia from occurring in dogs, since it is most commonly immune-mediated or caused by various diseases that are difficult to prevent. However, regular well-dog veterinary checkups can help undercover health issues, including thrombocytopenia, before they become too serious to treat.