An international collaborative study to establish the WHO 3rd International Standard for Thrombin: Communication from the ISTH SSC subcommittee on factor XIII and fibrinogen

Abstract

The 1st International Standard (IS) for thrombin endorsed by the World Health Organization (WHO) was established in 1975 to define the unitage of thrombin in terms of biological activity (international units, IU). 1 The standard was a partially purified preparation that also contained high amounts of proteolyzed forms of α-thrombin, known as β-and γ-thrombin. While α-thrombin clots fibrinogen, the clotting ability of β and γ forms is diminished, and they are only active toward synthetic substrates. 2,3 This necessitated an α-thrombin standard, which was established in 1991 from a high-purity preparation (coded 89/588, the 1st IS for α-Thrombin). 4 In parallel, the United States