Types of Inhibitors

Inhibitor levels vary from person to person. Over the course of time, inhibitor levels can also vary within the same person.3

These levels are called titer levels. Titer levels are used to define the type of inhibitor. Inhibitors can also be constant (last over a person's lifetime) or short-lived (last for a while, then go away).4,6

Titer Levels

Inhibitors are measured using a special blood test that counts the level of inhibitors present. This is called its titer level. Titer levels are measured in the number of Bethesda Units (BU) found.1

  • A low inhibitor titer has 0.5 to 5 BU.1
  • A high inhibitor titer has more than 5 BU.1
  • People with a low inhibitor titer are called low responders. Inhibitors have a weak or slow response.1,6
  • People with a high inhibitor titer are called high responders. Inhibitors tend to have a strong or fast response.1,6

Persistent and Transient Inhibitors

Inhibitors that are constant over a person's lifetime and do not go away are called persistent inhibitors. Persistent inhibitors may vary in their titer level. Persistent inhibitors are more common in people who are high responders.4

In some patients with low-titer inhibitors (< 5 BU), inhibitors may go away on their own. These are called transient (temporary) inhibitors, and usually go away without any special treatment.1,4