Who develops inhibitors?

Some people's immune system stops responding to standard treatment. Find out how and why.

Understanding factor inhibitors

About 1 in 5 people with hemophilia A and about 3 in 100 people with hemophilia B will develop an inhibitor to treatment. People with von Willebrand disease (VWD) type 3 may also develop inhibitors. Inhibitors can develop quickly after beginning treatment with factor VIII or factor IX medicines. Having a factor inhibitor makes it hard to use factor medicine for successful treatment.1,2

See one treatment option
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Who is at a higher risk?

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  • A family history of inhibitors
  • Black or Latino ethnicity
  • Severe hemophilia
    • Patients with mild or moderate hemophilia A develop factor VIII inhibitors at a rate that's 5%-10% less than patients with severe hemophilia A2
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  • With hemophilia, inhibitors develop usually within the first 10-20 days after starting factor replacement treatment
  • Inhibitors tend to appear after intensive factor replacement treatments with high doses, like after surgery
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  • In people with hemophilia, inhibitors are more likely to develop in early childhood before the age of 5 years, and especially during the first 50 days of factor-replacement treatment

Keep exploring

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Testing for inhibitors

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What are inhibitors?

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Connect with a Community Education Specialist

  1. Centers for Disease Control and Prevention. Inhibitors and hemophilia. https://www.cdc.gov/ncbddd/hemophilia/inhibitors.html. Accessed February 16, 2023.
  2. Srivastava A, Santagostino E, Dougall A, et al. WFH Guidelines for the Management of Hemophilia, 3rd edition. Haemophilia. 2020;26(suppl 6):1-158. https://doi.org/10.1111/hae.14046.
  3. Canadian Hemophilia Society. All about inhibitors. https://www.hemophilia.ca/files/All%20About%20Inhibitors.pdf. Accessed February 14, 2023.