Cat & Dog - Blood Clotting (Coagulation Tests)

Blood coagulation refers to a complex event which results in a blood clot.  Clotting occurs after any injury involving blood vessels or tissues in order to stop blood loss.  This process involves the interaction of specialised blood cells called platelets (whose function it is to plug the damaged blood vessel) and coagulation factors in the blood.

What are coagulation factors?

These are substances, manufactured in the liver, circulating in the blood which become active when blood vessel or tissue injury occurs.  With the platelets they produce a clot at the site of an injury.

Up to thirteen different coagulation factors have been identified that are all involved, 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 cause should also be evaluated
• Animals with severe liver disease may have to be tested since coagulation factors originate in the liver and therefore production may be reduced or completely stopped in a diseaased liver

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

The most commonly performed test is evaluation of platelet numbers.  This forms part of the Complete Blood Count (CBC).  Please see handouts on Preoperation check-ups and Routine 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 in cases of bleeding problems. Reduction in the number of red cells indicates anaemia may have occurred as a consequence of problems with coagulation factors or platelets, whereas an elevated white blood cell count may indicate an underlying inflammatory 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 Mucosa Bleeding Time (BMBT)

A specific test which can easily be performed in-house is the buccal mucosa bleeding time (BMBT test).  A tiny cut is made just inside the lip with a fine needle 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 impaired, this time will be prolonged.

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

Yes.  For these more specialised tests a separate 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.  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 relevant options.