Case 3: Classification of Inhibitors

Diagnosis established through measurement of inhibitor levels (inhibitor titer) in the blood

– Inhibitor titer is expressed in Bethesda units (BU)

• Higher the number of BUs, the more inhibitor present

– Low responders:

• Titer consistently < 5 BU
• ~60% of patients with inhibitors
• FVIII for replacement therapy may cause little or no increase in titer

– High responders:

• Titer consistently ≥ 5 BU
• ~40% of patients with inhibitors
• FVIII for replacement therapy may further stimulate inhibitor formation

Centers for Disease Control and Prevention. Available at: http://www.cdc.gov/ncbddd/hemophilia/inhibitors.html. Accessed April 24, 2013