Establishment of the First International Standard for Nucleic Acid Amplification Technology (NAT) Assays for HCV RNA

Abstract

Background and Objectives: The aims of this study were the establishment of a WHO International standard for HCV RNA for nucleic acid amplification technology (NAT) assays and the determination of the HCV RNA content of the candidate standard. Materials and Methods: Twenty–two laboratories evaluated three candidate materials (two lyophilised, AA and BB, which were derived from the same source and one a liquid preparation, CC). All samples were HCV genotype 1 with a concentration of approximately 10⁵ genome equivalents/ml. The methods used included the Roche Amplicor assay (version 1), Chiron Quantiplex (bDNA) assay, Organon Teknika NASBA assay, Transcription Mediated assay and various in–house assays, using single or nested primers. Results: There was reasonable agreement between the overall mean NAT detectable units/ml obtained by the different assays except for some of the in–house assays using single primers which gave substantially lower estimates. These titres were 5.0 log₁₀ for samples AA and BB and 4.6 log₁₀ for sample CC. Conclusions: Sample AA was accepted as the candidate standard and assigned a titre of 10⁵ international units (IU)/ml. The International Standard consists of a batch of vials each containing 50,000 IU/vial. Preliminary studies indicated that the material is stable at +4°C and +20°C for up to 200 days.