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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
≤1 Severe – frequent spontaneous bleeds from early life, joint deformity and crippling if not adequately treated
>1 to <5 Moderate – post-traumatic bleeding, occasional spontaneous bleeds
≥5 Mild – 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.