Background and objectives: Sixteen laboratories from 10 different countries participated in an international collaborative study to evaluate candidate materials as the first World Health Organization (WHO) International Standard for hepatitis A virus (HAV) RNA nucleic acid amplification technology (NAT) assays.
Materials and methods: Five candidate materials were analysed in this study: materials AA and BB were lyophilized, while materials CC, DD and EE were liquid preparations. Samples were diluted in pooled plasma or in pooled cryo-poor plasma (sample EE). Serial dilutions of the candidate materials were tested by each laboratory in four independent assays and the results were analysed statistically.
Results: The mean log(10)'equivalents' per ml were 5.29 for sample AA, 5.07 for sample BB, 4.99 for sample CC, 5.40 for sample DD and 4.08 for sample EE.
Conclusions: Based on the results of this study, sample AA was established as the first International Standard for HAV RNA NAT assays at the WHO Expert Committee on Biological Standardizaton (ECBS) meeting held in February 2003. The code number of this preparation is 00/560 and the potency, based on the study, is 100 000 International Units (IU)/ml.