| Abstract: | Summary. Advances in production technologies of factor (F)VIII concentrates during the last two decades has resulted in very pure and safe products. In assessment of recombinant FVIII:C, inconsistent assay values are found comparing one‐stage assays with two‐stage (e.g. amidolytic) methods. Such discrepancies have been quite prominent in the case of a B‐domain deleted recombinant FVIII (BDDrFVIII, ReFacto®). In order to alleviate this assay variance, a product‐specific reference standard the ReFacto Laboratory Standard? (RLS)], was established for laboratory use with either one‐stage clotting or chromogenic substrate assays for the measurement of FVIII:C in ReFacto‐containing patient samples. The primary objective of the current study was to assess, under field laboratory conditions, the accuracy and precision of the one‐stage clotting assay for the determination of FVIII:C in ReFacto‐containing samples employing the new concentrate standard. A secondary goal was to assess whether use of the RLS would minimize the discrepancy between one‐stage clotting and chromogenic substrate assays. Thirty‐one clinical laboratories worldwide participated in the study of severe‐hemophilic plasma (SHP) samples that had been spiked with ReFacto to target levels of 0.9, 0.6 and 0.2 IU mL?1. FVIII:C levels were determined against both the RLS and the local in‐house plasma standard (IHS). The results showed good agreement between laboratories in FVIII:C levels obtained by one‐stage clotting assays utilizing the RLS, and a good degree of accuracy was found compared with the intended target values. Consistent with previously published data, a discrepancy of approximately 30% was observed between one‐stage clotting and chromogenic potencies when the IHS was used as the calibrator. The discrepancy between one‐stage and chromogenic assay methodologies was significantly reduced when the RLS was employed as calibrator in the one‐stage assay. In conclusion, the study demonstrates that accurate and precise FVIII:C results can be obtained for ReFacto‐containing SHP samples by clinical laboratories using a product‐specific standard in one‐stage clotting assays. In addition, the product‐specific reference standard significantly reduced the discrepancy between the one‐stage clotting and the chromogenic substrate assay for ReFacto. |
