Blood Clotting (Coagulation Tests)

Coagulation refers to a series of events that result in the formation of a blood clot. Clotting occurs after any injury involving blood vessels or tissues in order to stop blood loss. This is a complex process involving mainly the interaction of specialised blood cells called platelets (whose function it is to plug the damaged blood vessel) and coagulation factors found in the blood.

What are coagulation factors?

These are substances manufactured in the liver that circulate in the bloodstream to become activated when blood vessel or tissue injury occurs. Together with platelets they produce a clot at the site of injury.

Up to thirteen different coagulation factors have been identified that are all interrelated, when required, in the production of a clot. Failure of any one of the major coagulation factors can result in haemorrhage which could be life threatening.

Some breeds of dogs are known to have a higher incidence of clotting factor deficiencies than others. In consequence it is prudent for such animals to undergo coagulation tests particularly prior to any contemplated surgery.

Coagulation tests

Coagulation tests are undertaken for a variety of reasons.

• Dogs of a breed or type known to have a higher incidence of clotting factor deficiencies should be tested prior to any surgical procedure.
• Pets experiencing bleeding episodes of unknown origin should also be evaluated
• Animals with severe liver disease may be tested since coagulation factors originate in the liver

Can any of these tests be performed in-house at the veterinary clinic?

The most commonly performed test is evaluation of platelet numbers. This forms part of the Complete Blood Count (CBC). Please see handouts: Pre-operation Checks and Blood Tests.

An abnormal decrease in total platelet numbers is called thrombocytopaenia. Causes of thrombocytopaenia include immune mediated diseases, bone marrow disorders and some infections. The CBC which measures total numbers of red and white cells is a useful test for cases of bleeding problems since reduction in the number of red cells indicating anaemia may have occurred as a consequence of decreased coagulation factors or platelets whereas an elevated white blood cell count may indicate an underlying inflammatory, immune mediated or infectious cause.

Since the clotting factors originate in the liver, serum biochemistry is always a useful test since this will give an indication of overall liver function.

Buccal Mucosal Bleeding Time (BMBT)

A specific test which can easily be performed in-house is the buccal mucosal bleeding time (BMBT test). A minute prick is made just inside the lip with a fine blade in a special instrument and the length of time for bleeding to stop is measured. If the number of platelets is decreased or their function is impaired, this time will be lengthened.

Are there any tests that can be used to measure coagulation factors?

Yes.  For these more specialised tests a single blood sample is required. This will be sent to a specialised laboratory. A variety of tests can be performed including individual coagulation factor analysis, the most common of which is estimation of von Willebrand's factor. (Please see handout on von Willebrand's Disease)

If the animal is found to have a blood clotting problem can anything be done?

This will depend upon the cause of the problem and therefore depends upon the individual case. Once the results are known we will be happy to discuss these and how they relate to your pet.