Calibration of the 7th British Working Standard for factors II, IX and X, concentrate.

Seven laboratories from 5 different countries participated in the calibration of the 7th British Working Standard (BWS) for blood coagulation factors II, IX and X. The candidate, 15/182, was assayed for Factors II and X potencies against the 4th International Standard (IS) for Factors II and X, Concentrate (11/126) and for Factor IX potency against the 5th IS for Factor IX, Concentrate (14/148). Intra-laboratory GCVs for all 3 factors were less than 10%, with the majority less than 5%. Inter-laboratory GCVs were 3.4%, 3.2% and 2.3% for FII, IX and X respectively. All participants agreed with the value assigned and preparation 15/182 was established by NIBSC in October 2017 as the 7th BWS for FII, IX, X Concentrate with potencies of 6.0 IU/ampoule, 6.7 IU/ampoule and 4.9 IU/ampoule for FII, IX and X respectively.