Hepatitis A immunoglobulin: An international collaborative study to establish the second International Standard

A collaborative study was carried out to assess the suitability of a candid ate replacement material for the International Standard for hepatitis A imm unoglobulin, which was found to be reactive for HCV RNA, and to calibrate i t in International Units. The candidate standard, coded 97/646, was derived from a bulk of 16% immunoglobulin supplied by the Central Laboratory of th e Netherlands Red Cross, Amsterdam, and diluted 1 in 2 in H2O resulting in a final immunoglobulin concentration of 8%. Sixteen laboratories from 11 co untries participated in the study and contributed data from 64 assays perfo rmed using six commercial assay kits and four in-house methods. All assays were analysed as parallel line bioassays comparing assay response with log concentration. The overall mean potency of the candidate replacement immuno globulin standard, 97/646, relative to the International Standard for hepat itis A immunoglobulin, was 98.6 IU/ml. A freeze-dried serum preparation, 97 /648, was also calibrated in this study and had a potency of 22.64 IU/ml. T he Second International Standard for hepatitis A immunoglobulin, human, was established by the World Health Organisation Expert Committee on Biologica l Standardisation in 1998 with a potency of 49 IU per ampoule when reconsti tuted in 0.5 mi.