The complex structure and function of coagulation factors, coupled with their low concentrations in blood plasma makes their estimation by physico-chemical means virtually impossible.  The estimation of coagulation factors therefore relies on the principle of comparative bioassay, relative to a reference standard containing a known amount of analyte.   Reference standards prepared locally can provide consistency and continuity of testing within a single laboratory but do not address the issue of harmonisation in testing between multiple laboratories.  International Standards (IS) established by the World Health Organization (WHO) fulfil this role by providing a common single route of calibration for all local and secondary working reference standards.  Since the introduction of this concept in 1925, with the development of an IS for the biological activity of insulin, there have been WHO IS developed in many and diverse areas of biological science and medicine.  The first IS for a coagulation factor, factor VIII (FVIII), was established in 1971 in response to the need for harmonisation in the potency labeling of the "new" therapeutic concentrates and this approach has subsequently been applied to most plasma coagulation factors and coagulation inhibitors.

 New areas under development:

• Factor XIII, concentrate
• Factor VIII inhibitors

QA studies:

We organise regular SSC Factor VIII & FIX (QA) Field studies on behalf of the ISTH/SSC FVIII/FIX Sub-committee