WHO/BS/2014.2245 Value assignment of the Candidate 1st IS for activated Blood Coagulation Factor XI (FXIa), Human, NIBSC Code 13/100

Overview

Seventeen laboratories from eleven different countries participated in a value assignment collaborative study for the proposed 1st International Standard for Activated Blood Coagulation Factor XI (FXIa), 13/100. Coded duplicates of the candidate together with 4 immunoglobulin preparations from 2 manufacturers were included in the study. In general the intra-laboratory variation was low indicating the laboratories were able to carry out FXIa quantitative assays with good precision. The inter-laboratory agreement was excellent for the candidate preparation with or without the inclusion of clot-based assay results; with GCV of 3.1 and 3.3% respectively. There was no assay discrepancy between the chromogenic and clotting assays. It is recommended that the value assignment should be based on functional chromogenic assays only.

It is therefore proposed that the candidate FXIa preparation, 13/100 be assigned as the WHO 1st International Standard for Activated Blood Coagulation FXI (FXIa), Human, with an assigned value of 9.8 International Units (IU) per ampoule