Practical and cost‐effective measurement of B‐domain deleted and full‐length recombinant FVIII in the routine haemostasis laboratory

Summary The assessment of recombinant FVIII (r FVIII ) activity ( FVIII : C ) in plasma of patients is dependent on the assay. Notably, a calibration with a product‐specific laboratory standard is recommended when measuring Refacto‐AF R activity in plasma with a one‐stage assay. The objective of this study was to facilitate the measurement of r FVIII , taking into account the recent demonstration that a calibration curve does not have to be included in each run. FVIII : C was measured in patients' samples after infusion of different types of r FVIII with a one‐stage and a chromogenic assay calibrated either with pooled normal plasma or a product‐specific laboratory standard. Results obtained with the one‐stage coagulation assay were compared with these provided by a chromogenic assay. We confirmed that a calibration curve can be used for a prolonged period of time without loss of precision and accuracy. In such conditions, a stable relation between the calibration curves generated with a product‐specific laboratory standard and plasma can be established. In patients' plasma, Refacto‐AF levels measured with a one‐stage FVIII assay calibrated with plasma or a product‐specific laboratory standard diverged from −58% to −17% and from −25% to +18%, respectively, from the activity determined with a chromogenic substrate assay. By comparison, FVIII : C levels of full‐length r FVIII measured with the one‐stage assay calibrated with plasma were 6–49% lower than with the chromogenic assay. In a monocentric setting, the long‐term stability of the calibration curves allows the implementation of a practical and cost‐effective approach to determine r FVIII : C levels.