Haemophilia is a condition that affects the ability of the blood to form clots in response to injury.
In a healthy person, a small cut or injury to the blood vessel leads to the release of substances in the blood known of as clotting factors.
These factors work together with blood cells and platelets to make the blood sticky, which eventually prevents bleeding.
In the case of haemophilia, however, there is a deficiency in these clotting factors in the blood, which means bleeding continues for longer than it should.
Haemophilia is an inherited condition that can be passed onto a child if one or both of their parents are affected.
Types of haemophilia
The two most common types of haemophilia are haemophilia A and haemophilia B, although most cases are haemophilia A. Also called factor VIII deficiency, haemophilia A is caused by a deficiency in factor VIII.
This clotting protein is produced by the liver and circulates in the blood bound to von Willebrand factor. Factor VIII acts in conjunction with active factor IX to activate factor X, which then works with its cofactor (factor Va) to activate thrombin.
The symptoms of haemophilia range from mild to severe depending on how deficient the clotting factors are. However, the majority of cases are severe and sufferers often experience internal bleeding.
Bleeding can occur around the joints and muscles leading to pain, stiffness and eventually joint damage. Females with haemophilia A may experience heavy bleeding during their periods as a symptom of the disease.
Diagnosis and treatment
Diagnosis is usually suspected based on blood tests that indicate poor coagulation. This is identified by an increased partial thromboplastin time in the context of a healthy prothrombin time and bleeding time. Diagnosis is confirmed if further blood testing reveals a very low level of factor VIII. Genetic testing is also now available to help determine whether a person is at risk of developing haemophilia or passing the condition on to any offspring.
Haemophilia cannot be cured but the condition can be managed with treatment to help a patient lead a normal quality of life. Over recent decades, genetically engineered clotting factor medications have been made available to help treat ongoing bleeding. This medication is administered as an injection which may be given only in response to bleeding in the case of mild haemophilia, or on a regular basis in the case of severe haemophilia.
Reviewed by Sally Robertson, BSc