Inhibitors are antibodies that are made by our immune system. In general, when your immune system identifies a foreign substance, it makes antibodies that will specifically recognize that substance and destroy it to defend you from harmful diseases and/or illnesses. Because the immune system thinks the foreign substance is attacking the body, antibodies — or inhibitors — are produced to destroy that substance. Sometimes the immune system makes a mistake and produces an inhibitor that destroys natural protectors of the body. Scientists aren't sure why this happens.1
When these inhibitors attack the clotting factor, the inhibitors neutralize the factor therapy and stop it from working.1 Since the hemophilia still needs to be treated, other treatment options need to be considered.2
The good news is that there are treatment options available to help manage bleeding episodes in hemophilia patients who develop inhibitors. People who have hemophilia with inhibitors can learn to successfully manage their hemophilia and lead happy lives.3
Having an inhibitor does not lead to more frequent bleeding episodes than those with hemophilia who do not have inhibitors.4
Inhibitors can develop quickly after beginning treatment with factor medicines—usually within the first 5-50 days. Having an inhibitor makes it hard to use factor medicine for successful treatment.1
"If you've had more than 50 factor exposures, then your chances of developing inhibitors are less." — Susana, Takeda community educator
Certain factors may increase the chances that an inhibitor will develop.1
The general risk guidelines show a higher chance of children with severe hemophilia developing inhibitors. Yet, the truth is, inhibitors cannot be prevented, and they can happen at any time.1,6
An inhibitor is suspected whenever a bleeding episode is not controlled by a patient's usual dose of replacement clotting factor. Inhibitors are also diagnosed in individuals without symptoms based on the results of routine blood tests.6
Inhibitors are measured using a test called the Bethesda assay, which gives a numeric value and refers to the inhibitor level. This number is quantified in Bethesda units per milliliter (BU/mL) and refers to the inhibitor level. Knowing the level is important. It helps the hemophilia care team decide the best type of treatment to use.6
Inhibitor levels vary from person to person. Over the course of time, inhibitor levels can also vary within the same person.1
Inhibitors are divided into 2 categories based on the Bethesda assay and whether the inhibitor level increases when a patient is treated with replacement clotting factor:
Low-responding inhibitors remain less than 5 BU/mL. These inhibitors may be transient and disappear.1,7
High-responding inhibitors are equal to or greater than 5 BU/mL at any time. In the absence of replacement clotting factor exposure, high-responding inhibitors may decrease or become undetectable. However, when the patient is re-exposed to replacement clotting factor, this inhibitor level will increase over 4 to 7 days. This increase is termed anamnesis and is a hallmark of the high-responding inhibitor.1,3,7
You're not alone. More than 30% of hemophilia patients face inhibitors to their treatment.
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