An international collaborative study to establish a World Health Organization international standard for hepatitis B virus DNA nucleic acid amplification techniques

Background and objectives Twenty-two laboratories from nine countries parti cipated in an international collaborative study to establish a World Health Organization (WHO) international standard for hepatitis B virus (HBV) DNA nucleic acid amplification techniques (NAT). Materials and methods Three samples, AA, BB (both of which were lyophilized ) and CC (which was a liquid preparation), were analysed using several diff erent NAT assays. The mean HBV DNA content of each sample was determined fr om the study. Results Despite the range of assays (commercial and in-house) used by parti cipants, there was good agreement among the overall mean 'equivalents'/ml o btained by the different assays, except for one laboratory (laboratory 4). The variation in estimates of log(10) 'equivalents'/ml was 1.75-1.25 for th e three samples if results from laboratory 4 were excluded. The mean log(10 ) 'equivalents'/ml for all laboratories were 6.42 for sample AA, 6.30 for s ample BB and 5.03 for sample CC (exclusion of results from laboratory 4 mad e little difference). The difference in titres between the two lyophilized samples (AA and BB) was not statistically significant but the titre of the frozen sample (CC) was significantly lower. Material AA (code 97/746) was a ccepted as the first WHO international standard for HBV DNA NAT assays and assigned a potency of 10(6) international units (IU)/ml. Conclusions The titres (genome equivalents/ml) of three HBV preparations we re determined by several laboratories using different NAT assays. This stud y enabled the establishment of an international standard, 97/746, for HBV D NA NAT assays.