The activity of a Factor VIII inhibitor can be expressed in a different units depending on the assay.



(1) Bethesda units

(2) New Oxford units


1 Bethesda unit of inhibitor activity per mL will reduce Factor 8 activity in a sample by 50%.


number of Bethesda units =

= 1.2 * (number of Oxford units)


number of Oxford units =

= 0.83 * (number of Bethesda units)


Cautions in interpreting Factor VIII inhibitor activity:

(1) The conversion factor may vary from sample to sample (see Table 7, page 75, Austen, 1982).

(2) The number of inhibitor units does not imply that the sample can be neutralized by infusion of the comparable amount of Factor VIII.


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