Which test is used to quantitate a factor inhibitor?

Which test is used to quantitate a factor inhibitor?

• A. Factor assay
• B. Multimer test
• C. Ristocetin cofactor
• D. Bethesda assay

Answer: (D)

Quantifying a factor inhibitor relies on measuring how much antibody neutralizes a clotting factor, most commonly factor VIII in hemophilia A. The Bethesda assay is designed for this: it mixes patient plasma with normal plasma and incubates the mixture so any inhibitors can act on the factor. After incubation, the remaining activity of the factor is measured. The amount of inhibitor present is expressed in Bethesda units, where one unit equals the amount of inhibitor needed to neutralize 50% of the factor activity in normal plasma under the defined conditions. This gives a quantitative readout of inhibitor strength, not just its presence. The other tests serve different purposes. A factor assay shows how much of a given coagulation factor is present or functional, not how strongly it’s inhibited. Multimer testing and ristocetin cofactor assess von Willebrand disease features and VWF function, respectively, not inhibitors of clotting factors.

Quantifying a factor inhibitor relies on measuring how much antibody neutralizes a clotting factor, most commonly factor VIII in hemophilia A. The Bethesda assay is designed for this: it mixes patient plasma with normal plasma and incubates the mixture so any inhibitors can act on the factor. After incubation, the remaining activity of the factor is measured. The amount of inhibitor present is expressed in Bethesda units, where one unit equals the amount of inhibitor needed to neutralize 50% of the factor activity in normal plasma under the defined conditions. This gives a quantitative readout of inhibitor strength, not just its presence.

The other tests serve different purposes. A factor assay shows how much of a given coagulation factor is present or functional, not how strongly it’s inhibited. Multimer testing and ristocetin cofactor assess von Willebrand disease features and VWF function, respectively, not inhibitors of clotting factors.