Establishment of the WHO 2nd International Standard Factor V, plasma (16/374): Communication from the SSC of the ISTH.

The WHO International Standard (WHO IS) for Factor V in plasma defines the International Unit (IU) for factor V clotting activity and thereby supports the quantification, harmonisation and long-term continuity of measurements internationally. Measurement of factor V in plasma is pertinent to the diagnosis of rare bleeding disorders as well as being a quality control marker for solvent-detergent treated fresh, frozen human plasma [1,2]. Declining stocks of the WHO 1st IS (NIBSC code: 03/116) has made it necessary to prepare a replacement standard and this report describes the value assignment of the WHO 2nd IS Factor V plasma (16/374) for clotting activity and a new analyte, factor V antigen. This article is protected by copyright. All rights reserved.