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Canine Blood Clots: Symptoms, Diagnosis, Causes, and Treatments

By Roxanne Hawn

Dogs can develop a blood clot (also called a thrombus) anywhere in the body. These clots may stay in the location they form, or they may embolize, which means a clot breaks loose and lodges somewhere else.

Canine Blood Clot Locations and Symptoms

Blood clot symptoms depend on where the clot blocks blood flow – partially or completely. Typically, you won’t know a clot is forming until it becomes an emergency situation.

“Wherever [the clot] lodges, it causes an acute cessation of blood flow. That’s where you’re going to see clinical signs,” says Justin C. Mathis, DVM, MS, DACVECC, assistant professor of small animal emergency and critical care at Colorado State University Veterinary Teaching Hospital.

Brain: “With clots that go to the brain, you’re going to see an acute change in mentation, or mental function,” Mathis says. “[Patients] are going to be dull, sometimes even comatose, depending upon the degree of the clot and where it lodged.”

Heart: “We see clots go through the heart,” explains Mathis, “but they don’t commonly lodge in the heart.” This is one area where the degree of blood flow restriction is especially important for determining symptoms. Patients with large obstructions are at risk for more serious symptoms according to Dr. Mathis: “If the clot is big enough to cause a full obstruction, they will just pass out.”

Lungs: Clots that form in or embolize to the lungs cause acute breathing distress. Clots in the lungs are also quite painful.

Limbs: If a clot forms in a dog’s limbs, which happened to my Border Collie a few months before she died, you’ll see a dog somewhat suddenly lose the ability to use one or more limbs. Often, the affected limb(s) will feel cold to the touch because of the decrease in blood flow.

Gastrointestinal Tract: “You’re probably going to see acute abdominal pain. You might see vomiting or diarrhea,” Mathis says of clots in the GI tract.

Canine Blood Clot Diagnosis

Because other medical problems can cause many of these same symptoms, veterinarians typically begin with a thorough physical exam, urinalysis, and basic blood work, including a complete blood count and full biochemistry analysis.

If signs point to a blood clot in a limb, for example, your veterinarian may also run a blood test for lactate in that limb compared to lactate in your dog’s other limbs. “Lactate is a metabolic byproduct, so lactate is increased in the leg, if there is no blood flow or no oxygen being delivered,” Mathis says.

Veterinarians also can run blood tests that check for clotting. The prothrombin time test measures how long it takes for a clot to form. The other, more comprehensive test for coagulation is called thromboelastography. “It can really tell you if they are hyper- or hypo coagulable. That tells you if they are more prone or less prone to clot,” Mathis explains.

Typically in an emergency setting, veterinarians can get those test results back in about an hour.

If a clot appears likely, your veterinarian may also recommend taking medical images to understand the extent and location of the clot. These methods might include:

  • MRI or CT scan for clots in the brain
  • CT scan for clots in the lungs
  • Ultrasound for clots in the limbs, heart, or near kidneys and liver

Canine Blood Clot Causes

“There is a laundry list of things the can cause a clot,” Mathis says. These include:

  • Trauma (like being hit by a car or taking a bad fall), which causes an inflammatory cascade
  • Endocrine diseases such as Cushing’s Disease
  • Autoimmune diseases of all kinds (especially immune-mediated hemolytic anemia)
  • Cancer (both diagnosed and not-yet diagnosed)
  • Infections and inflammatory diseases
  • Protein loss through the GI tract or kidneys
  • Certain medications (especially long-term use of corticosteroids)
  • “We know in both human and veterinary medicine that inflammation and coagulation are ingrained with each other…One begets the other. Once you have an inflammatory process, you can definitely see an animal form a clot,” Mathis says.

    Canine Blood Clot Treatments

    When determining the course of treatment, veterinarians must decide if it’s enough simply to keep an existing clot from getting worse and to prevent new clots from forming. This can be accomplished using medications such a clopidogrel bisulfate (Plavix) or heparin. In some cases it is necessary to try breaking up the existing clot. “There are benefits and risks to both,” Mathis says.

    The good news is that our bodies, as well as our dogs’ bodies, already have many mechanisms in place to deal with blood clots over time. “As you can imagine,” Mathis says, “when there is an acute obstruction of blood flow, we need to fix things as fast as possible – ideally.”

    The challenge of actively trying to break up an existing clot through medications is that you turn one big clot into many little ones that can travel and lodge elsewhere.

    “That’s why a lot of the time, we don’t necessarily treat the clot or the thrombus that has formed. We treat them supportively otherwise,” Mathis says. For example, veterinarians might provide oxygen therapy for dogs with clots in the lungs, fluid therapy for dogs with clots affecting the kidneys, and physical therapy for dogs with clots in their legs.

    “Ultimately, you have to treat the underlying disease that’s causing [the patient] to form the thrombus,” Mathis says.

    In some cases, if you provide the right level of medical support and treat the underlying disease long enough, dogs can recover from even severe blood clots. Mathis once treated a dog with endocarditis (an infection in the heart) who formed a large clot that resulted in complete rear leg paralysis. The dog’s family provided a high level of care in the weeks and months that followed. Six weeks after the initial treatment she could walk again with assistance. Today, she is strong enough to drag Mathis down the hospital hall when she comes to visit.

    The discovery and treatment of a blood clot can be a scary experience for both dogs and those who love them. The symptoms are often both sudden and surprising. While blood clots are indeed an emergency situation and require immediate attention, in some cases a full recovery is possible with proper treatment.

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