WHO/BS/2016.2281 Collaborative study on the 2nd IS for Blood Coagulation Factor XI, Plasma (15/180)

Overview

The aims of this study were to assign Factor XI functional activity to the 2nd International Standard (IS) for Blood Coagulation Factor XI, Plasma, and to additionally assign a new analyte, FXI antigen, to the same International Standard. Assignment of the functional activity value in International Units (IU) was performed by one-stage clotting assay by 29 laboratories, relative to the 1st IS. The majority of intra-laboratory GCVs were less than 5% and the inter-laboratory variability was extremely low at 1.8%, with an overall geometric mean of 0.71 IU/ampoule. The antigen value assignment was performed by 11 laboratories and was calculated relative to normal plasma pools. As is customary with new coagulation factor analytes, the amount of analyte present in 1 ml of normal plasma was taken to be 1 unit, therefore the assignment of antigen is in IU/ampoule relative to normal plasma pools. The inter-laboratory variation of the antigen assays was acceptable at 10%, with an overall geometric mean of 0.78 IU/ampoule.