Inhibitors

In some cases, when a person receives replacement factor, the body perceives the normal clotting factor as foreign, and the immune system produces an antibody to fight it. Such antibodies are calledinhibitors.The inhibitor binds to the infused clotting factor, making it difficult or impossible to obtain a level sufficient to control bleeding.

Infusions of clotting factor won’t provide the same long-term positive outcomes as they would in the absence of inhibitors. Less than optimal treatments can lead to secondary problems, such as infections, bleeding in the joints, and organ damage.

Between 20 and 30 percent of people living with hemophilia can develop inhibitors sometime in their life and over the course of treatment. Inhibitors occur more often in those with a severe form of the condition. About 15 to 35 percent of people with hemophilia A will develop inhibitors to factor VIII. Inhibitors are much less common in those with hemophilia B—less than 5 percent develop them.

Inhibitors are most likely to develop in those who:

  • Have severe hemophilia
  • Have a relative who had an inhibitor
  • Are younger than 20 years old
  • Are of African-American or Hispanic descent

Many times, a person won’t show any symptoms. Inhibitors are often discovered through lab tests taken during regular doctor visits. Inhibitors can be suspect if bleeding doesn’t stop after treatment with factor concentrate. Their presence can be confirmed through a blood test called a Bethesda inhibitor assay. This test measures the number of antibodies directed against a coagulation factor in a person’s blood after receiving factor.

For people with inhibitors (antibodies to factors VIII and IX), treatment decisions are complicated. The care of those with inhibitors should be urgently discussed with the hematologist. Treating a person who has inhibitors is challenging and often a twofold process: first, managing the bleed; second, dealing with the inhibitor itself. Treatment can take months or even years.

Because of the complexities, many doctors believe that ridding the body of inhibitors is the best option, using an approach known asimmune tolerance.Different variations of this therapy are available, but most require repeated exposure to the missing clotting factor. People who opt for immune tolerance receive daily doses of factor over a period of weeks or years. Some also receive drugs to suppress the immune system, but this can predispose them to infection. The goal of immune tolerance therapy is to teach the body to tolerate the factor, but the risks should be thoroughly discussed with the healthcare provider. Overall, immune tolerance therapy is viable and considered effective in 60 to 80 percent of all cases.

For those who have low-responding inhibitors (low levels of inhibitor in the blood), continued therapy with factor replacement is often possible. This approach can control both minor and more serious bleeds. To overcome the presence of inhibitors, doctors may prescribe larger and possibly additional doses of factor.

For people with high-responding inhibitors, standard factor often isn’t an option because the inhibitor will neutralize even large doses. Specialty products that bypass factors VIII and IX in the clotting cascade are usually needed. Treatment is based on the type of hemophilia and the nature of the bleed.In some cases, when a person receives replacement factor, the body perceives the normal clotting factor as foreign, and the immune system produces an antibody to fight it. Such antibodies are called inhibitors. The inhibitor binds to the infused clotting factor, making it difficult or impossible to obtain a level sufficient to control bleeding.


Infusions of clotting factor won’t provide the same long-term positive outcomes as they would in the absence of inhibitors. Less than optimal treatments can lead to secondary problems, such as infections, bleeding in the joints, and organ damage.


Between 20 and 30 percent of people living with hemophilia can develop inhibitors sometime in their life and over the course of treatment. Inhibitors occur more often in those with a severe form of the condition. About 15 to 35 percent of people with hemophilia A will develop inhibitors to factor VIII. Inhibitors are much less common in those with hemophilia B—less than 5 percent develop them.


Inhibitors are most likely to develop in those who:

❂Have severe hemophilia

❂Have a relative who had an inhibitor

❂Are younger than 20 years old

❂ Are of African-American or Hispanic descent


Many times, a person won’t show any symptoms. Inhibitors are often discovered through lab tests taken during regular doctor visits. Inhibitors can be suspect if bleeding doesn’t stop after treatment with factor concentrate. Their presence can be confirmed through a blood test called a Bethesda inhibitor assay. This test measures the number of antibodies directed against a coagulation factor in a person’s blood after receiving factor.


For people with inhibitors (antibodies to factors VIII and IX), treatment decisions are complicated. The care of those with inhibitors should be urgently discussed with the hematologist. Treating a person who has inhibitors is challenging and often a twofold process: first, managing the bleed; second, dealing with the inhibitor itself. Treatment can take months or even years.


Because of the complexities, many doctors believe that ridding the body of inhibitors is the best option, using an approach known as immune tolerance. Different variations of this therapy are available, but most require repeated exposure to the missing clotting factor. People who opt for immune tolerance receive daily doses of factor over a period of weeks or years. Some also receive drugs to suppress the immune system, but this can predispose them to infection. The goal of immune tolerance therapy is to teach the body to tolerate the factor, but the risks should be thoroughly discussed with the healthcare provider. Overall, immune tolerance therapy is viable and considered effective in 60 to 80 percent of all cases.


For those who have low-responding inhibitors (low levels of inhibitor in the blood), continued therapy with factor replacement is often possible. This approach can control both minor and more serious bleeds. To overcome the presence of inhibitors, doctors may prescribe larger and possibly additional doses of factor.


For people with high-responding inhibitors, standard factor often isn’t an option because the inhibitor will neutralize even large doses. Specialty products that bypass factors VIII and IX in the clotting cascade are usually needed. Treatment is based on the type of hemophilia and the nature of the bleed.

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