Bethesda inhibitor assay is for measuring the amount of antibody against factors in Hemophilia A and B.

• A. Coagulation factor levels in Hemophilia A and B
• B. Platelet function
• C. Measuring the amount of antibody against factors in Hemophilia A and B
• D. Iron studies

Answer: (C)

The Bethesda inhibitor assay measures neutralizing antibodies against the clotting factors, specifically factor VIII in Hemophilia A and factor IX in Hemophilia B. In some patients, these inhibitors arise and block the activity of the replacement factor, undermining standard therapy. The test works by combining a patient’s plasma with normal plasma containing a known amount of the relevant factor and then measuring how much factor activity remains after incubation. The result is expressed in Bethesda Units per milliliter, where one unit represents the amount of inhibitor that reduces the factor activity by 50% under defined conditions (usually 37°C for 2 hours). A higher inhibitor titer indicates a stronger immune response against the factor, guiding treatment toward bypassing agents or immune tolerance strategies rather than routine factor concentrates. This assay specifically targets antibodies against the coagulation factors and does not measure platelet function or iron studies, nor does it simply report factor levels.