Factor VIII Inhibitor Assay
Purpose:
-
To demonstrate the presence of inhibitor to FVIII
for diagnostic and therapeutic purposes.
Method:
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The Bethesda Assay is the most commonly used:
1. Mix patient's plasma with normal human plasma (which contains
factor VIII)
2. Mix a control plasma with normal human plasma.
3. Allow the mixtures to incubate at 37 degrees Celcius for 2
hours.
4. Measure residual factor VIII in both the patient mixture and
the control mixture.
5. Express the residual factor VIII in the patient mixture as
a percentage of that in the control plasma.
6. The Bethesda inhibitor titer is the reciprocal of the dilution
of patient sample which yields residual FVIII = 50% of control.
Interpretation:
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A positive Bethesda Assay usually indicates the presence of a specific
FVIII inhibitor.
-
For example, if a 1:5 dilution of patient's plasma yields residual FVIII
of 50%, then that dilution contains 1 unit/ml of inhibitor. The undiluted
plasma, then, contains 5 units/ml of inhibitor.
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