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Severity of haemophilia

The severity describes how serious a problem is. The level of severity depends on the amount of clotting factor that is missing from a person’s blood.  

LevelPercentage of normal factor activity in bloodNumber of international units (IU) per millilitre (ml) of whole blood
normal range  50%-150%   0.50–1.5 IU
mild haemophilia  5%-40%   0.05–0.40 IU
moderate haemophilia   1%-5%   0.01­–0.05 IU
severe haemophilia   less than 1%   less than 0.01 IU







People with severe haemophilia usually bleed frequently into their muscles or joints. They may bleed one to two times per week. Bleeding is often spontaneous, which means it happens for no obvious reason.

People with moderate haemophilia bleed less frequently, about once a month. They may bleed for a long time after surgery, a bad injury, or dental work. A person with moderate haemophilia will rarely experience spontaneous bleeding.

People with mild haemophilia usually bleed only as a result of surgery or major injury. They do not bleed often and, in fact, may never have a bleeding problem.