blood clot


What is haemophilia?

The general term haemophilia describes a group of inherited blood disorders in which there is a life-long defect in the clotting mechanism of the blood. Blood contains many proteins called clotting factors, and these work to stop bleeding. The lack of clotting factor causes people with haemophilia to bleed for longer periods of time, than people whose blood factor levels are normal. However, people with haemophilia do not bleed faster than other people.

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Figure 1: The normal clotting process

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Figure 2: The clotting process in a person with haemophilia, where a clotting factor is missing. 

Most bleeding in haemophilia occurs internally, into the joints or muscles. The joints that are most often affected are the knee, ankle and elbow. Repeated bleeding without prompt treatment can damage a joint. The incidence of haemophilia in the general population is 1 in 10,000 (therefore about 1 in 5,000 of the male population has haemophilia).

There are two types of haemophilia. Haemophilia A which is a deficiency in factor VIII and haemophilia B (sometimes called Christmas Disease) is a deficiency in factor IX. Both types of haemophilia share the same symptoms and inheritance pattern, only blood tests can differentiate which factor is affected. The severity of the condition is related to the degree of deficiency of the relevant clotting factor in the blood.

Severity of haemophilia

Percentage of normal factor activity in blood

Number of international units (IU) per millilitre (ml) of whole blood

normal range


0.50–1.5 IU

mild haemophilia


0.05–0.40 IU

moderate haemophilia


0.01­–0.05 IU

severe haemophilia

less than 1%

less than 0.01 IU

Those who have mild or moderate haemophilia generally only experience bleeding problems after an obvious injury or an operation and many mild cases have only been after, for example, a tooth extraction or surgery.

Haemophilia is a genetic blood disorder, which is usually inherited. The gene is passed down from a parent to a child. A person who is born with haemophilia will have it for life. Some of the signs of haemophilia are; large bruises, bleeding into muscles and joints, spontaneous bleeding and bleeding for a long time after a cut or surgery.

Click here to download a copy of the I.H.S. publication \’Introduction to Haemophilia\’