Activated Clotting Time (ACT) in Dogs

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Clotting time, or coagulation time, is the time required for blood to clot outside of the body. Clotting is a protective mechanism to prevent the dog’s body from bleeding, and many different proteins are involved in the various steps of coagulation. An abnormality at any point during the steps of coagulation can result in prolonged bleeding, and without treatment, bleeding disorders can sometimes lead to death.

One of the tests used to help determine a possible cause for a bleeding disorder is the activated clotting test. An activated clotting time is indicated in any dog with a suspected coagulation or bleeding problem. This test is also performed before procedures in which there may be a clotting concern such as a liver biopsy.

There are no real contraindications to performing this test. In dogs with bleeding abnormalities, it is possible for the needle stick to cause bleeding, so special care must be taken by applying pressure at the sight, using a bandage or drawing the blood from a small vein.

What Does an Activated Clotting Time Reveal in Dogs?

An activated clotting time reveals the time it takes for blood to clot and is considered a crude measure of the intrinsic clotting system. Of the more than 12 clotting proteins involved in forming a blood clot, the activated clotting time tests Factors XII, XI, IX and VIII. Normal activated clotting time in dogs is 60 to 120 seconds and 60 to 70 seconds in the cat but this can vary from lab to lab. Values longer than normal indicate a potential bleeding disorder. The most common cause of a prolonged activated clotting time is anticoagulant rodenticide poisoning.

How Is an Activated Clotting Time Done in Dogs?

In order to perform an activated clotting time, your veterinarian must draw a blood sample, which is placed in a pre-warmed special glass tube. The tube is then gently rocked back and forth and checked every 5 seconds for clot formation. Once a clot forms, the test is complete and the time noted. Some veterinary hospitals have an in-house machine that tests the blood without the need to check for a clot manually. The test typically takes less than 10 minutes to run.

Is an Activated Clotting Time Painful to Dogs?

Any pain involved is associated with the collection of the blood sample, since a needle is used to pierce the skin and enter a blood vessel to draw the sample. As with people, the pain experienced from a needle will vary from individual to individual.

Is Sedation or Anesthesia Needed for an Activated Clotting Time?

Neither sedation nor anesthesia is needed in most patients; however, some dogs resent needle sticks and may need tranquilization or ultrashort anesthesia.

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