Hemophilia is a bleeding disorder in which the blood doesn't clot properly. Normally, when a wound occurs coagulation (or clotting) takes place, which turns the liquid blood into a gel in order to form clot which stops the bleeding.
This process is known as hemostasis.
There are three steps involved in this.
There are 13 coagulation factors which are numbered from 1 - 13 in Roman numerals. If any one of these 13 coagulation factors is deficient or missing, hemophilia can occur.
Most cats with hemophilia have inherited it (inherited coagulopathies), however it is also possible for a cat to develop hemophilia at any time in his life (acquired coagulopathies).
Hemophilia is usually inherited as an X linked recessive trait (inherited from the mother) males are mostly affected as the faulty gene is on the X chromosome, and the male only has one, he develops the condition. Female cats have two X chromosomes, which means they can carry the faulty chromosome, but won't develop hemophilia themselves as their 'normal' X chromosome (remember they have two X chromosomes) is enough to prevent hemophilia. While males are most often affected, it is possible for a female to have hemophilia if a male with hemophilia mates with a female carrier, and the two X female chromosomes both have the faulty gene.
- Hemophilia can also develop as a result of vitamin K deficiency. This vitamin plays a vital role in the synthesis of coagulation factors in the liver. This is most commonly associated with rodenticide poisoning.
- Liver disease is another cause of hemophilia in cats due to the liver synthesising coagulation factors.
Hemophilia is the most common type of bleeding disorders to affect cats.
Types of hemophilia in cats:
- Factor VIII deficiency, this is the most common form of hemophilia in cats and is due to a deficiency of coagulation factor 8.
- Factor IX deficiency (sometimes called Christmas disease).
- Factor XII (Hageman factor) deficiency. This form of hemophilia typically does not express a bleeding tendency and is usually discovered accidentally when routine blood coagulation testing reveals a very long activated partial thromboplastin time (APTT). 
A breed predisposition has been linked to Devon Rex, British Shorthair, Siamese and Maine Coon cats and has been seen in mixed breed cats.
What are the symptoms of hemophilia in cats?
Symptoms of hemophilia usually present before the cat reaches adulthood. Bleeding may occur due to a trauma such as a scratch or wound, internal bleeding may also occur. Severity of bleeding depends on the amount of clotting factor missing from the cat's blood.
- Cats with a severe deficiency in affected factors often die at birth.
- Protracted bleeding following injury and/or surgery. This is commonly seen in young cats during desexing (spaying or neutering). Bleeding is usually milder in cats with hemophilia B.
- Prolonged bleeding due to lost deciduous (baby) teeth.
- Bruising and swelling under the skin due to hematomas. These often go unnoticed due to the cat's fur covering most of the skin.
Other symptoms due to anemia or internal bleeding may also be present and include:
- Severe weakness.
- Pale mucous membranes.
- Blood in the vomit or stool.
- Bleeding from the nose, rectum, gums.
- Swelling in the abdomen due to internal bleeding.
- Limping due to bleeding into the joints.
- Rapid breathing.
- Difficulty breathing.
- Loss of appetite.
How is hemophilia in cats diagnosed?
Your veterinarian will perform a complete physical examination of your cat and obtain a medical history from you.
In vivo bleeding time may be carried out. This involves either cutting the nail just slightly into the quick or pricking the nose to determine how long it takes for bleeding to stop.
Coagulation assays are a series of tests to measure clotting time and include:
- aPTT (activated partial thromboplastin time).
- Prothrombin time.
- Thrombin clotting time.
- Fibrinogen determination - This test measures levels of fibrinogen in the blood plasma.
In addition, your veterinarian may want to perform routine screening tests such as biochemical profile, complete blood count (which may reveal anemia) and urinalysis.
How is hemophilia treated?
There is no cure for cats with inherited hemophilia. Treatment of hemophilia depends on the severity of the disease.
- Severely affected cats will require blood transfusions either with fresh whole blood if the cat is anemic or plasma to replace active coagulation factors.
- Surgery should be avoided where possible in cats who have hemophilia. Where it is necessary, they should receive a blood transfusion prior to surgery.
- Intermittent transfusions may be required for bleeding events.
- Vitamin K may be prescribed.
For cats who have acquired hemophilia due to rodenticide poisoning:
- Induce vomiting.
- Activated charcoal.
- Vitamin K injection followed by long term (30-45 days) vitamin K administered orally.
Home care and preventing hemophilia in cats:
- All affected cats should be kept indoors and should not be bred with.
- Daughters of affected males are obligate carriers and should also be desexed.
- Avoid strenuous active play to reduce the risk of bleeding into the joints.
- Avoidance of certain medications with anticoagulant properties such as NSAIDs.
- Maintain excellent oral hygiene to avoid gum disease which can cause the gums to bleed.
What is the prognosis for cats with hemophilia?
The prognosis is good for cats with mild to moderate hemophilia, however it is guarded in severe cases.
 Dr Lowell Ackerman Cat Health Encyclopedia, p. 151
Blood clot image courtesy Michael Tam.