Haemophilia
& Treatment
What are Inhibitors?
The Basics
Patients with haemophilia generally receive treatment (known as 'factor replacement therapy') to help their blood to clot.
Some patients develop antibodies to their haemophilia treatment. Antibodies are produced by the immune system to destroy foreign substances the body perceives as foreign.
The antibodies to haemophilia treatment are known as 'inhibitors'.
The inhibitor neutralises the haemophilia treatment preventing it from doing its job.
The strength of an inhibitor (called inhibitor titre) is measured by the Bethesda Assay and reported in Bethesda Units. People are described as having either a low or high titre inhibitor depending on its strength.
Inhibitors can appear after only a few treatments and are classified by a patient's level of antibody response to the injected factor. If their body produces large quantities of antibodies (high titre) in response to their injection of factor, they are known as a high responder. If the level of antibody is low (low titre) and does not increase much after an injection of factor they are known as a low responder.
In addition, people with acquired haemophilia also have inhibitors - but they produce antibodies to their own clotting factor. In this case their immune system believes the body's own clotting factor is foreign and makes antibodies (inhibitors), which neutralise it (click here for more information).
Advanced
Inhibitors are antibodies to a clotting factor.
People who have developed inhibitors are classed as either high-or low-responders.
The expression 'high responder' or 'low responder' refers to the way an individual's inhibitor reacts to an infusion of clotting factor.
The strength of an inhibitor (called inhibitor titre) is measured by the Bethesda Assay and reported in Bethesda Units, so people may have a high or low titre inhibitor.
How common are inhibitors?
Inhibitors are less common in those with haemophilia B and those with mild or moderate haemophilia A. It occurs most often in patients with severe haemophilia A.
It has been estimated that approximately 30% of severe haemophilia A patients will develop an inhibitor. However, most inhibitors are transient (temporary/acute) and the prevalence (number of severe haemophilia A patients that have permanent/chronic inhibitors at a given time) is approximately 10%.
The prevalence of inhibitors in mild/ moderate haemophilia A patients is approximately 13%
Less than 5% of people with severe or moderate haemophilia B develop inhibitors.
Inhibitors tend to develop more frequently during childhood, usually within the first 50 infusions of factor replacement therapy and when children's immune systems are developing.
