Haemophilia is a bleeding disorder, seen in humans and dogs as well as cats. It can be a cause of death in kittens and young cats but is thankfully rare. There are two types of haemophilia in cats, and both are inherited conditions and can be passed down the family line. Without a specific genetic test, it’s important not to breed from affected cats, to prevent increasing numbers of cases of this incurable condition. 

What is haemophilia?

Haemophilia is an inherited bleeding condition in which the affected cat’s blood doesn’t clot properly. In normal cats, proteins in the blood called clotting factors mix with platelets at the source of a bleed to form a clot, which prevents further blood loss. With haemophilia, the genes that control the production of these clotting factors are altered, leading to a deficiency. There are a lot of different clotting factor proteins, and they are named using Roman numerals (I-XIII).

There are two types of haemophilia seen in cats. Haemophilia A is the more common type seen in cats and is due to a deficiency in Factor VIII. Haemophilia B is less common and is due to a deficiency of Factor IX. 

What are the symptoms?

The symptoms of haemophilia vary slightly, depending on the severity of the lack of clotting factors. Patients are mostly diagnosed at a young age, usually before a year old. Severely affected cats (less than 1% of normal clotting factors) may die at birth, or shortly afterwards. Cats with higher levels may show no symptoms until they undergo a surgical procedure or obtain an injury. 

Signs include:

  • Weakness and fatigue
  • Loss of appetite
  • Prolonged bleeding after surgery or injury
  • Gums bleeding during eruption of adult teeth
  • Lameness (due to bleeding into joints)
  • Swelling or bruising under the skin (haematomas)
  • Internal bleeding leading to bloody/dark vomit or faeces, bloody discharge from anus or genitals, nose bleeds, swollen abdomen or breathing difficulties
  • Bleeding into the eyes leading to blindness
  • Bleeding into the brain causing neurological symptoms such as collapse or seizures

What cats can get haemophilia?

Fortunately, haemophilia is rare in cats.1

Haemophilia A and B are both genetic conditions, inherited from the parents. They are also sex-linked, with the mutation found only on the X chromosome. Female cats have two X chromosomes, but males have only one. If a male cat inherits the mutation on their X chromosome, they will be clinically affected with the haemophilia disease. If a female inherits the mutation on just one X chromosome, they will be a carrier but will not show any signs of haemophilia. This is because the condition is recessive, requiring both X chromosomes to be affected. Haemophilia is therefore much more common in males, but can be passed down to kittens via a seemingly unaffected queen. For a female cat to be clinically affected by haemophilia, both parents would have to be carrying the mutated gene. 

Haemophilia A is a more common type than Haemophilia B in cats. Both are generally diagnosed in young cats under 1 year old and are mostly found in non-pedigree domestic cats, although cases have been reported in various purebreds, including a Siamese-cross cats, Birmans, British Shorthair cats and Himalayans.2 

Treatment and management

There is no cure for haemophilia. Cats with a severe lack of clotting factors will often die from huge blood loss at a young age. Cats with only mild-moderate deficiencies may be managed by a strictly non-traumatic lifestyle (e.g., keeping indoors to restrict falls, accidents, and fights). Acute bleeds may require transfusions of whole blood or fresh frozen plasma. Your vets will be able to advise you on how to manage your cat’s individual condition, should haemophilia or another clotting disorder be suspected.

Can we test for haemophilia?

Haemophilia can be diagnosed in cats using tests to measure clotting factors and clotting times. There is no specific test, as yet, for the genetic mutation. This makes screening for haemophilia more difficult, especially with the large potential for female carriers who do not themselves have haemophilia. It is recommended for breeders to test any cats showing clinical signs for haemophilia before breeding, and to avoid breeding from any cat with an affected relative. 


  1. Barr JW and McMichael M (2012) Inherited disorders of hemostasis in dogs and catsTopics In Companion Animal Medicine 27: 53–8
  • Brooks M and DeWilde L (2006) Feline Factor XII DeficiencyCompendium on Continuing Education for the Practicing Veterinarian28: 148–155