What is haemophilia A?

Haemophilia A is a bleeding disorder that means your blood cannot clot properly.

Blood contains lots of clotting factors, which interact with each other in a sequence to make a clot form. This is called the ‘clotting pathway’. People with haemophilia A do not have enough of one of these clotting factors – factor eight (factor VIII).

Haemophilia A can be described as mild, moderate or severe, depending on how much FVIII is in the blood.

People with severe haemophilia A have <1% FVIII and people with moderate haemophilia A have between 1-5%. Some people with moderate haemophilia A can bleed more than others. This is often referred to as having “a severe bleeding phenotype”.

The clotting pathway is a bit like dominoes falling, watch our video to find out more about haemophilia A and the clotting cascade

Translated versions of this video can be viewed in

and

The clotting cascade

This illustration represents factors in the clotting pathway that are relevant to haemophilia A.

Factor VIII is the link between activated factor nine (factor IXa) and factor ten (factor X).

When factor IXa falls, factor VIII needs to be in place so that it can fall on to the factor X domino.

If factor VIII is missing, the rest of the dominoes will not fall and a clot will not form.

Haemophilia A can be managed with factor VIII replacement therapy. Factor VIII therapy can be used to help blood clot in response to injury. It can also be administered regularly, to help prevent bleeds from happening. Taking a treatment regularly to try and prevent bleeding is called prophylaxis.

Useful resources

View all our useful resources in one place, from booklets and guides to videos and animations

View useful resources