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Testing and Diagnosis

An inhibitor is suspected whenever a bleeding episode is not promptly controlled by a patient’s usual dose of replacement clotting factor.¹ Inhibitors are also diagnosed in individuals without symptoms based on the results of routine blood tests.

Inhibitors are measured in a test called the Bethesda assay, which gives them a numeric value.¹ This number, which can range from less than 1 to over 1000, is quantified in Bethesda units, abbreviated BU, and is referred to as the inhibitor titer or the antibody titer.

Are all inhibitors the same?

Inhibitors are divided into 2 categories based on the Bethesda assay and whether the inhibitor titer increases when a patient is treated with replacement clotting factor.

Low-titer, low-responding inhibitors remain at 5 BU or lower.² These inhibitors may be transient and disappear. They may also be recurrent, coming and going throughout a person’s lifetime.^3,4

High-titer, high-responding inhibitors measure more than 5 BU² and rise when a patient receives replacement clotting factor.^4,5 This increase is termed anamnesis. A high-responding inhibitor may drop below 5 BU if a patient does not receive replacement clotting factor for several months. However, once factor is given, anamnesis will occur, and the inhibitor titer will increase.¹ High-titer, high-responding inhibitors are usually persistent^4,5 and account for an estimated 50% of all factor VIII inhibitors.^3,4

If you are diagnosed with an inhibitor, your hemophilia treatment center (HTC) will work with you to create an individualized management plan that takes into consideration your current inhibitor titer and your lifestyle and activities.

References

1. Kasper CK. Diagnosis and management of inhibitors to factors VIII and IX. An introductory discussion for physicians. Treatment of Hemophilia; September 2004, no.34.
2. White GC, Rosendaal F, Aledort LM, Lusher JM, Rothschild C, Ingerslev J. Definitions in hemophilia. Recommendation of the scientific subcommittee on factor VIII and factor IX of the scientific and standardization committee of the International Society on Thrombosis and Haemostasis. Thromb Haemost. 2001;85:560.
3. Lusher J, Abildgaard C, Arkin S, et al. Human recombinant DNA-derived antihemophilic factor in the treatment of previously untreated patients with hemophilia A: final report on a hallmark clinical investigation. J Thromb Haemost. 2004;2:574-583.
4. Leissinger CA. Prevention of bleeds in hemophilia patients with inhibitors: emerging data and clinical direction. Am J Hematol. 2004;77:187-193.
5. Ho AY, Height SE, Smith MP. Immune tolerance therapy for haemophilia. Drugs. 2000;60:547-554.

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Note: thereforyou.com does not recommend a particular treatment for specific individuals and recommends that you consult your hemophilia treatment center or physician before pursuing any course of treatment.