Comparison of the factor VII : C clot analysis and a modified activated factor VII analysis for monitoring factor VII activity in patients treated with recombinant activated factor VII (NovoSeven (R))

Bleeding episodes in haemophilia A and B inhibitor patients are now frequen tly treated with recombinant activated factor VII (NovoSeven(R), Novo Nordi sk A/S, Bagsvaerd, Denmark). Until now, the FVII:C coagulation assay has be en used to monitor NovoSeven(R)-mediated coagulation. However, a new assay (Staclot VIIa-rTF, Diagnostica Stage, France) has been designed to specific ally detect activated factor (F)VII. Replacement of the buffer supplied by the manufacturer with a PIPES buffer containing BSA (modified FVIIa assay), resulted in a linear standard curve, greater sample stability and a reduce d coefficient of variation. The FVII:C assay and the modified FVIIa assay w ere compared in a recovery experiment using the International FVIIa standar d No 89/688(IS). Recovery of FVIIa was 93-97% for the modified FVIIa assay and 91-115% for the FVII:C assay. However, because samples in the FVII:C as say were not parallel to the standard curve, confidence limits for recovery were as wide as 67-130% compared with 92-106% for the FVIIa assay. In conc lusion, a modified version of the Staclot VIIa-rTF assay, suitable for moni toring treatment with NovoSeven(R), even at low concentrations, has been de veloped. It provides an alternative to the FVII:C assay, which is not suita ble for monitoring FVIIa at low concentrations. Blood Coagul Fibrinolysis 1 1 (suppl 1):S159-S164 (C) 2000 Lippincott Williams & Wilkins.