Table 3.

Diagram of the inhibitor method adopted for surveillance by the Centers for Disease Control and Prevention (CDC)

CDC Modification of the Nijmegen-Bethesda Method
Heat patient and control plasmas to 56°C and centrifuge.
Dilute patient plasma in VIIIDP* if an inhibitor is expected.
Patient Mix	Control Mix
1 part patient or dilution: 1 part BNPP**	1 part VIIIDP:1 part BNPP
↘	↙
Incubate for 2 hours at 37°C.
Measure Factor VIII activity.
Patient mix/control mix X 100 = % residual activity (RA)
Convert RA to NBU by formula.
Adjust for dilution, if necessary.
Nijmegen modifications: BNPP used in mixes, VIIIDP used to dilute plasma and in control mix; CDC modification: heating of plasma to destroy infused and endogenous FVIII

^*VIIIDP=factor VIII-deficient plasma

^**BNPP=imidazole-buffered normal pooled plasma