WHO/BS/2017.2326 Collaborative Study on the 1st IS for Blood Coagulation Factor XII, Plasma:  Assignment of Functional (FXII:C) and Antigen values (FXII:AG)

Overview

Twenty laboratories took part in a collaborative study to value assign additional analytes of blood coagulation factor XII function (FXII:C) and antigen (FXII:Ag) to the 2 nd International Standard for FXI, Plasma, NIBSC code 15/180. The value assignment was against local normal pooled plasma were assumed to have 1 u/ml of functional activity or antigen content. For FXII:C, 28 sets of results from one stage clotting assays using 13 different APTT reagents against local plasma pools with a total of 566 donors were returned. The intra-laboratory geometric coefficient of variation (GCVs) ranged from 1-20%, with the majority being less than 10%. The overall geometric mean was 0.86 IU/ampoule, with inter-laboratory GCV of 10%. For FXII:Ag, 9 sets of results obtained using 3 different commercial kits/paired antibody set and 1 in-house reagents were analysed against local plasma pools with a total of 216 donors. The intra-laboratory GCVs ranged from 4-12%, with the majority being less than 10%. The overall geometric mean was 0.80 IU/ampoule, with inter-laboratory GCV of 11%.

Proposals for establishment: 

To establish additional values for FXII:C and FXII:Ag to the current 2nd IS for FXI, Plasma:

FXII:C – 0.86 IU/ampoule and FXII:Ag – 0.80 IU/ampoule