Haemophilia B

Test Overview:

Haemophilia B is a clotting disorder and occurs due to a deficiency of an essential clotting factor in the blood (clotting factor IX).  This disease is inherited (recessively) on the X chromosome, and hence is seen in male animals (who only have one copy of the X chromosome).  Haemophilia B is also sometimes called Christmas disease.  It is similar to haemophilia A, but in general causes less severe bleeding. The severity of the bleeding disorder seen with haemophilia B depends on how much active factor IX an affected cat has, compared to normal.  If the factor IX level is very low then spontaneous bleeding may occur.  Signs may include lameness (due to bleeding into the joints), pain due to bruising under the skin, weakness and lack of appetite (due to anaemia), and severe life-threatening bleeding after trauma or minor surgery.  With moderately low levels of factor IX affected cats may be normal until undergoing surgery, at which time there may be massive, life-threatening bleeding. Haemophilia B results in an increase in the activated partial thromboplastin time (APTT), a test which measures part of the clotting process and can be tested at a veterinary laboratory.  Your vet may recommend this test prior to surgery to screen for haemophilia B.  There is no cure for haemophilia B, and treatment of bleeding episodes is supportive.  Blood transfusions may be required, and it is also important to note that the British shorthair has a relatively high incidence of blood type B.  A genetic test to screen for haemophilia B is available, although many different mutations have been shown to cause this disease in cats, so genetic testing is of little benefit in many cases.