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What is the difference between haemophilia A and B?

The differences between haemophilia A and B are in the factor that is missing or at a low level – haemophilia A means low levels of factor VIII (8) and haemophilia B is low levels of factor IX (9). This means that the treatment given to replace the factor is different – haemophilia A needs to be treated with factor VIII and haemophilia B with factor IX replacement. Giving factor VIII to someone with haemophilia B won’t help to stop the bleeding.

Haemophilia A and B are both bleeding disorders that are congenital (passed on at birth through the genes), and are caused by a low level or absence in one of the ‘factors’ normally found in the blood that help make a stable blood clot. A poor blood clot will mean that a person is at risk of bleeding internally, and most often inside the joints or muscles. This can happen when moving normally or exercising or straining, or due to an injury, and a clot will take longer to form and stop the bleeding.  The person is also at risk of re-bleeding when the poor blood clot that is formed breaks down too soon.

People with zero levels of factor are described as having severe haemophilia, and these people are at most risk of bleeding. People with higher levels up to the normal ranges are described as having moderate or mild haemophilia, and the risk of bleeding is less for someone with mild haemophilia.

People with severe haemophilia often will give themselves protective injections of the missing factor (called prophylaxis) to raise their levels and prevent bleeds from happening. People with mild haemophilia usually will only need treatment if they are injured or need surgery.

These points above are the same whether you have haemophilia A or B.

Answered by: Nurse

Date last reviewed: 3 November 2021

Important Note: This information was developed by Haemophilia Foundation Australia for education and information purposes only and does not replace advice from a treating health professional. Always see your health care provider for assessment and advice about your individual health before taking action or relying on published information. This information may be printed or photocopied for educational purposes.

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