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Hemophilia at a glance
What is hemophilia? Hemophilia is a blood disorder in which the blood doesn’t clot properly due to a lack of clotting proteins (coagulation factors). It can be acquired or congenital.
Symptoms: Excessive bleeding, bruising under the skin, and in severe cases, anemia can develop.
Diagnosis: A variety of blood clotting tests.
Treatment: Avoid surgery unless necessary, blood transfusions and vitamin K.
Hemophilia is a bleeding disorder in which the blood doesn’t clot properly; it is the most well-known of the bleeding disorders to affect cats.
When a wound occurs, coagulation (or clotting) occurs to turn the liquid blood into a gel to form a clot and stop blood loss, this is called hemostasis, and there are three steps in this process.
When a blood vessel becomes damaged, vasoconstriction occurs, making the blood vessel smaller, which restricts the loss of blood from the damaged site.
When damage to a blood vessel occurs, circulating platelets form a clump over the damaged vessel to block it off.
Fibrinogen is activated by clotting proteins known as coagulation factors in the blood-forming fibrin strands. These strands help to mesh the platelet plug, strengthening it.
There are 13 coagulation factors from 1 – 13 in Roman numerals. If any 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).
Causes of hemophilia in cats
Hemophilia is usually inherited as an X linked recessive trait. Males are most affected as the faulty gene is on the X chromosome, as males only have one X chromosome, he develops the condition.
Female cats have two X chromosomes (one from each parent), which means they can carry the faulty chromosome, but won’t develop hemophilia themselves as their ‘normal’ X chromosome 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 often due to ingestion of rat poison.
Liver disease as the liver is responsible for the synthesis of coagulation factors.
- Hemophilia A: Factor VIII deficiency, this is the most common form of hemophilia in cats and is due to a deficiency of coagulation factor 8.
- Hemophilia B: Factor IX deficiency (sometimes called Christmas disease) and is reported to be inherited in British Shorthair cats.
- Factor XII (Hageman factor) deficiency: This form of hemophilia typically does not express a bleeding tendency and is usually an incidental finding when routine blood coagulation testing reveal 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 domestic cats.
Symptoms of hemophilia usually present before the cat reaches adulthood. Bleeding may occur due to a trauma such as a scratch or a wound. The severity of bleeding depends on the amount of clotting factor missing from the cat’s blood. Kittens with a severe deficiency in affected factors often die at birth.
- Protracted bleeding following injury and/or surgery which may first occur when the cat is spayed or neutered. Bleeding is usually milder in cats with hemophilia B.
- Prolonged oral bleeding when the baby teeth are replaced by adult 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
- Difficulty breathing
- Loss of appetite
Your veterinarian will perform a complete physical examination of your cat and obtain a medical history from you.
- In vivo bleeding time: This test 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: 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.
- Baseline tests which include biochemical profile, complete blood count, and urinalysis.
There is no cure for cats with inherited hemophilia and treatment will depend on the severity of the disease.
- Cats with severe hemophilia may need blood transfusions either with fresh whole blood if the cat is anemic or plasma to replace active coagulation factors.
- Avoid surgery where possible and where it is necessary, blood transfusion prior to surgery.
- Intermittent transfusions may for bleeding events.
- Vitamin K injection.
For cats who have acquired hemophilia due to rodenticide poisoning:
- Induce vomiting with medications.
- Activated charcoal to bind to the toxin.
- Vitamin K injection followed by long-term (30-45 days) vitamin K administered orally.
- Keep affected cats indoors and spay or neuter.
- Desex daughters of affected males as they are obligate carriers.
- 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.
The prognosis is good for cats with mild to moderate hemophilia, however, it is poor in cats with severe hemophilia.
 Dr Lowell Ackerman Cat Health Encyclopedia, p. 151
Blood clot image courtesy Michael Tam.