Hemophilia: Understanding inhibitors

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Teens living with hemophilia can learn about inhibitors, what they are and how they affect treatment.

Trying to wrap your head around inhibitors and how they work may seem tricky. But inhibitors can be an easy concept to grasp, especially if you’re a football fan. Click on the animation to learn how inhibitors affect hemophilia treatment and how different types of therapy can help.

How inhibitors work

Let’s use a football game to understand what happens inside your bloodstream when you treat a bleed. During a game, the goal is to try to get the football past defense and into the ‘end zone’ – the area at the other end of the field. Think of the football as factor; the football field is your bloodstream; and the end zone is the location of your bleed. During a football game, the defensive players try to prevent the football from getting into the end zone. Think of these defensive players as inhibitors. As you will learn, inhibitors can vary in strength.

A football team without a defense is just like a person with hemophilia who does not have any inhibitors. It is easy for factor to get into the end zone and stop the bleed because there are no defenders to “inhibit” the play.

Some inhibitors do not completely prevent factor from working. They just slow down factor, so that it is less effective. These are called low-titre inhibitors. This is similar to having only one defense player on the field. Sometimes these low-titre inhibitors resolve over time. If bleeding occurs, a person with a low-titre inhibitor may need more factor than usual to treat a bleed.

As more defensive players move into the field, it is going to be even harder to get the football into the end zone. This is similar to developing a strong inhibitor, which tackles factor, preventing it from reaching the bleeding joint. Stronger inhibitors are called high-titre inhibitors. In this case, doctors will have to adjust the treatment plan. The strongest inhibitors are the most difficult ones to treat. Increases in factor dosing may not work.

How do inhibitors work?

This is a click-through animation of the concept described above. The animation is supplemental and repeats information from the body text.

Bypassing agents

One option to get around the strong inhibitor defense is to use special factors called bypassing agents. These agents can avoid the high-titre inhibitors completely, much like a lateral pass in football that is thrown over and past the defense players. Bypassing agents are an effective strategy to treat people with inhibitors.

Immune tolerance therapy (ITT)

If you develop a high-titre inhibitor, doctors may put you on a treatment plan called immune tolerance therapy or ITT.

In ITT, doctors give you strategic doses of the product that you are missing. By giving you doses of factor at regular intervals over the course of several months or years, your body gets used to it. ITT helps your body build a ‘tolerance’ to product; it trains the body to recognize factor without reacting to it. The goal of ITT is to stop your body from making “defense players", thus resolving the inhibitors.

ITT is usually effective: studies show that ITT works about 80% of the time. Some people with hemophilia who have inhibitors may be on ITT for six months; others may be on it for up to two years or longer.

Once your body develops a good tolerance to the product, you still need to follow the advice of your comprehensive care team (CCT). In rare cases, the inhibitor can come back.

Diagnosing inhibitors

To determine the presence and amount of inhibitors in your blood, doctors need to run a blood test. If we think back to the football analogy, the test is like the Football Scouting Combine. In the Scouting Combine, university or college football players perform various mental and physical tests so scouts can determine their level of fitness. For a person with hemophilia, doctors will look for the number of inhibitors (defense players) and check to see how strong these inhibitors are.

The testing helps doctors distinguish between low and high-titre inhibitors. If the number ends up being high then your team knows that they are up against a high-titre inhibitor; low counts are low-titre inhibitors. Depending on which one it is, your CCT will come up with different “plays” to get your factor into scoring range and hopefully the end zone.

Living with an inhibitor

About 30% of people living with severe hemophilia will have inhibitors to factor. Living with an inhibitor is a very different story today than it used to be. A lot of research in hemophilia is focused on making products and treatment safer for you to use. Treating inhibitors with the bypassing agents and immune tolerance therapy (ITT) are now readily available even for home care. These treatment options are effective and can give you a similar quality of life to a person who has severe hemophilia without inhibitors.

Last updated: March 13th 2019