Factor VIII test in reference preparations: compensation for different dilutions

An approach is described that aims to prevent the problems associated with factor VIII (FVIII) assays. This approach takes a number of factors into consideration: 2 different assay types are currently being performed (clotting and chromogenic), different standards coexist (for plasma and for concentrates) and not only are reference standards being diluted for test purposes, but likewise plasmas are diluted by adding reference standards which are significantly less concentrated than commercial concentrates. Moreover, artificially FVIII-depleted plasmas are diluted as compared to normal or haemophilic plasma with respect to non-FVIII proteins as well. Taken together, these observations have led us to re-examine FVIII assays and to establish an algorithm for FVIII measurements with plasma as the natural reference.