A collaborative study was undertaken to assess the suitability of a replacement for the First International Standard for parvovirus B19 IgG, human serum and to calibrate it in IU. The proposed standard. which is a pool of sera from 16 US blood donors, was assayed along with the First International Standard, a coded duplicate or the proposed standard and a plasma sample from a single blood donor. Nine laboratories from eight countries participated in the studies and five different assay kits were used. Two kits contained VP1 + VP2, one kit contained VP1 only and two kits. one of which was used by five participants contained VP2 only. Differences in detection of the proposed standard and the individual plasma were observed with as say kits containing different antigens, VP1, VP2 or VP1 + VP2. However, since VP1 is a minor capsid protein and on its own does not assemble into virus Dike particles and the dominant response in individuals appears to be against VP2. it was considered reasonable to utilize only the data from kits containing VP2 antigen for the calibration of the proposed standard. The results of this study demonstrated that the proposed standard coded 011602 was suitable to serve as the replacement International Standard for parvovirus B19, serum IgG, and this preparation was established as the Second International Standard for parvovirus B 19 antibody, plasma human, with an assigned unitage of 77 IU per ampoule by the Expert Committee on Biological Standardisation of the World health Organisation in February 2003. (C) 2004 The International Association for Biolgoicals. Published by Elsevier Ltd. All rights reserved.
