Prothrombin Time in Dogs

Clotting, or coagulation, of blood is a protective mechanism to limit blood loss by hemorrhage. Many different proteins are involved in the various steps of the coagulation cascade. Dysfunction at any stage of the process will prolong bleeding. Without treatment, bleeding disorders sometimes result in death of affected animals.

One of the tests used to help determine the possible cause of the bleeding disorder is the prothrombin time (PT). Testing PT is indicated in any pet with a suspected coagulation problem. This test is also performed prior to procedures in which it is important to establish that blood clotting is adequate, e.g. liver biopsy.

There are no contraindications to performing this test. In pets with bleeding problems, it is possible for the venipuncture to cause excessive bleeding from the site, so special care must be taken by a) drawing the blood from a small vein and b) by applying pressure at the injection site for longer than usual.

What Does a Prothrombin Time Reveal?

Prothrombin time is a measure of the time it takes for blood plasma to clot. It is used to evaluate the proper functioning of certain coagulation proteins. The test detects deficiencies in the extrinsic and common pathways. Of the 12 clotting proteins involved in clotting, PT tests Factors X, VII, V, II and I. Several of these clotting factors rely on vitamin K for proper function. Normal PT in dogs is less than 22 seconds, but this can vary from laboratory to laboratory. Values greater than 22 seconds indicate a potential bleeding disorder. The most common cause of a prolonged PT is poisoning with an anticoagulant rodenticide.

How Is a Prothrombin Time Done?

In order to check PT, your veterinarian must first draw a blood sample, which is then placed inside a special glass tube. This sample is often submitted to a laboratory for analysis. Some veterinary clinics, and most veterinary emergency facilities, have the capability to run a PT test in their hospital. Others rely on outside laboratories. In emergency situations, PT can be run at a local human hospital for rapid results. The test typically takes less than 10 minutes to run once the blood is available. However, if the blood is submitted to an outside laboratory, the results may not be available for 1 to 2 days.

Is Testing Prothrombin Time Painful?

The only pain involved is associated with collection of the blood sample. The pain associated with this procedure varies from individual to individual, as it does in humans.

Is Sedation or Anesthesia Needed to check Prothrombin Time?

Neither sedation nor anesthesia is needed in most patients. However, pets that resent needle sticks and may benefit from sedation.