An inhibitor is an antibody that prevents factor replacement treatment from working. When an inhibitor develops, it binds to factor concentrates such as factor VIII or factor IX, stopping them from working and making bleeding more difficult to treat.

Of people with severe haemophilia A, about 30 per cent will develop inhibitors; among those with mild and moderate haemophilia A, the figure is about 9 per cent. However, only 3 per cent of people with haemophilia B will develop an inhibitor. In very rare cases, people with other bleeding disorders can also develop inhibitors.

Known risk factors in the development of inhibitors include:

  • severity of the bleeding disorder
  • ethnicity
  • family history of inhibitors
  • number of days treated with clotting factor concentrate

Inhibitors typically develop in the first 50 treatment days, with most developing in the first 20 days. This is why when people with severe haemophilia develop inhibitors, it is usually during childhood, whilst people with mild or moderate conditions tend to develop them later in life.

Inhibitors are treated with immune tolerance induction(ITI). ITI involves regular exposure to factor treatment with the aim of the body becoming accustomed to the clotting factor. Studies show that the body often stops rejecting the system by flooding the system with factor VIII or factor IX.

It is recommended that children with inhibitors start ITI therapy as early as possible and usually continue without interruption for 12 months or longer. If an inhibitor does not respond to ITI other treatment options may need to be considered.

If you or someone in your family are living with an inhibitor or have recently been diagnosed with an inhibitor you can join our dedicated Facebook Inhibitor Support Group or contact our Inhibitor Ambassador on [email protected]

More Information

More information on Inhibitors can be found on the European Haemophilia Consortium Inhibitor website.