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)