WHO/BS/2020.2384 WHO 3rd IS for Thrombin

Overview

Background: An international collaborative study was organised to calibrate a replacement for the WHO 2nd International Standard for Thrombin (01/580), stocks of which are running low. Twenty laboratories from 13 countries were asked to measure the potency of two candidate replacement standards relative to the 2nd IS (designated sample S), using their in-house plasma or fibrinogen clotting assays and/or chromogenic assays. Sample A (01/578) was used in the previous international collaborative study in 2002 to establish the 2nd IS and samples B and C were coded duplicates of a newly ampouled material donated by a manufacturer (coded 19/188).

Results: Nineteen laboratories contributed a total of 111 assays after exclusions, which comprised 91 clotting assays, 56 with fibrinogen and 35 with plasma. Of these, 52 were performed with automated coagulometers, 12 with manual coagulometers, and 27 with microtitre plate-based assays. Four laboratories performed chromogenic assays (16 assays in total) and one laboratory performed fluorogenic assays (4 assays). Variation between and within laboratories was low, with inter- and intra-laboratory geometric coefficient of variation (GCV) generally < 5 % for all assay methods and substrates. For sample A (01/578), potency estimates by clotting assays (101.1 IU/ampoule, inter-laboratory GCV = 3.5 %) were significantly lower than estimates by chromogenic assays (111.5 IU/ampoule, inter-laboratory GCV = 4.4 %), in good agreement with the 2002 study. The estimate by fluorogenic assay was midway between clotting and chromogenic.