Haemophilia A

Haemophilia A is due to a deficiency of Factor VIII. Although a rare condition, this is one of the most common of the clotting factor deficiencies. The genetic defect is sex-linked and approximately 1 in 10,000 are affected. Depending on the concentration of Factor VIII in the blood, patients with haemophilia are classified as having a severe, moderate or mild condition. (See table below).

Table 1 - Correlation of coagulation factor activity and severity in Haemophilia A and B

Coagulation Factor Activity (% normal*)Clinical Manifestation
≤1Severe - frequent spontaneous bleeds from early life, joint deformity and crippling if not adequately treated
>1 to <5Moderate - post-traumatic bleeding, occasional spontaneous bleeds
≥5Mild - post-traumatic bleeding
* Normal is 100% and is defined as 100 international units (IU) of the factor per dL of blood. 'Normal' coagulation factor activity can range from 50 - 200%. About one-third of carriers have low or subnormal activity. In normal pregnancy, activity levels may exceed 200%.

If untreated, patients with severe deficiencies may have frequent spontaneous bleeding into joints and muscles; they bleed excessively during minor surgery (e.g. tooth extraction) and may suffer life-threatening bleeding from trauma or even relatively minor injury. Replacement of the missing Factor VIII corrects the bleeding problem. Patients with severe haemophilia are usually treated at home injecting themselves either prophylactically or when they experience a bleed - the latter known as 'on demand' treatment.