Excessive Blood Clotting in Cats

By PetMD Editorial on Jan. 30, 2009

Hypercoagulability in Cats

Blood platelets are minute, disc shaped cell fragments in the blood that are responsible for clotting the blood. Too many active platelets, or too few active platelets, can result in severe health disorders. One of these disorders, hypercoagulability (hyper-clotting), has several causes, but in essence it reflects a greater amount of procoagulants than anticoagulants in the blood. This means that the blood coagulates (clots) abnormally more than usual. One of the possible causes of hypercoagulability is when there are too many active platelets in the blood. The end result of hypercoagulability is an episode of thrombosis, where clots will get trapped in arteries, veins, or in the heart, causing a loss of blood to the areas these arteries feed. Hypercoagulability is usually secondary to an underlying disease.

Symptoms and Types

A blood clot that is blocking arteries in the lungs will present as severe breathing difficulties that come on suddenly. Rapid breathing, lack of energy, and possible fever are also be symptoms of an arterial blood clot. A blood clot blocking the aortic artery – the major artery from the heart to the body – will show as sudden weakness or paralysis, pain in the limbs, an absent or weak pulse in the arteries on the inside of the thigh, cold limbs, or blue-purple colored nails


Hypercoagulability onset may be due to blood platelets that are stickier than normal, resulting in too much clotting of blood cells; deficiencies in antithrombin, a natural anticoagulant that prevents clotting in the arteries and veins; decreased removal of coagulation factors - that is, not enough procoagulants are being removed, resulting in an abundance of coagulating factors; or, defective fibrinolysis. Fibrinolysis is the process where fibrin, the protein end product of blood coagulation, is dissolved, resulting in the removal of small blood clots from the bloodstream.

Some of the other causes for this condition are:

  • Protein-losing nephropathy: a condition which causes a loss of protein from the intestines so that anti-clotting/anticoagulant proteins are lacking
  • Immune-mediated hemolytic anemia: the abnormal breakdown of blood vessels
  • Disseminated intravascular coagulopathy: a serious disease of the blood vessels, which is usually secondary to a life-threatening illness, or precipitated by a bacterial infection in the blood (sepsis)
  • Inflammation of the pancreas
  • Parasite infection: specifically with Dirofilaria, a genus of worms that includes the heartworm
  • Under-functioning thyroid gland
  • Cancer


Since hypercoagulability is usually the result of an underlying disease, your veterinarian will order tests for activated partial thromboplastin time (APTT) to measure how quickly your cat's blood is clotting, in addition to a blood chemical profile, a complete blood count, and a comprehensive urinalysis.

Chest x-rays will help to visualize abnormalities in the lungs, and an abdominal ultrasound may be used to further examine the body for an aortic artery blockage. An echocardiogram can also be used, for diagnosing blood clots in the heart, and for detecting high blood pressure in the lungs that may be present due to blood clots there.

An examination using an injection of a radiopaque substance in order to view the blood vessels, called angiography, may also be necessary for confirming a blood clot. Another test, called nuclear perfusion scintigraphy, uses a radioactive tracer to illuminate the internal body, and is useful for noninvasively diagnosing blood clots in the lungs.


If necessary, your veterinarian will hospitalize your cat for anticoagulant and fluid therapy. Your cat's activity will be severely restricted until the condition has reversed. Bed rest is essential when an animal has a blood clot blocking an artery, since physical activity can rush the clot into an essential supply organ or vein. For this reason, your cat will be placed on oxygen cage therapy if the blood clot is in the arteries or the lungs. If the underlying disease causing hypercoagulability cannot be resolved, subsequent clotting episodes will probably occur.

If anticoagulant medicines are indicated, your veterinarian will decide how much, and how long to administer these medicines. The course of medication and therapy will be dependent on the amount of time it takes for your pet’s blood to clot after treatment.

Living and Management

You will need to schedule check-ups with your veterinarian to monitor your cat's prothrombin times (clotting times) twice a week following discharge from care. After that, your doctor will probably begin scheduling your cat for weekly check-ups over several weeks, until it is certain that the condition has been resolved. Once this stage has been reached, your cat can be seen once about every two months or more.

Help us make PetMD better

Was this article helpful?

Get Instant Vet Help Via Chat or Video. Connect with a Vet. Chewy Health