The concentrations of the quantitation standards (QS) of several artus® kits are stated as IU/µl (international units per µl). Is it possible to convert this concentration unit into copies per µl?

For a variety of pathogens (HIV, HBV, HCV, Parvovirus B19, HAV) international units (IU) have been determined by the World Health Organisation (WHO) for the establishment of worldwide comparable pathogen diagnostics. Conversion factors are documented in a WHO report to allow a recalculation from IU/vol. to copies/vol. ("WHO Consultation on International Standards for in vitro Clinical Diagnostic Procedures based on Nucleic Acid Amplification Techniques (NAT)", 2002). However, QIAGEN considers the conversion of IU into copies not permissible or, at least, misleading. The conversion of concentration units is thought to allow a comparison of results generated with different detection assays. However, since the quantitation standards of many competitive products are not calibrated with international standards, these conversions may lead to discrepant results. Hence, these conversions do not contribute to a comparability of different assay results but may rather obscure conclusions. QIAGEN calibrates all artus^® quantitation standards using international standards if available (e.g. from the National Institute for Biological Standards and Control, UK; www.nibsc.ac.uk). If the quantitation standards of a competitive product were adjusted correspondingly, the assay results may indeed be compared. Please also note paragraph 3.2.2. in the European "IVD guideline on common technical specifications for in vitro-diagnostic medical devices" which clearly states that international reference material has to be used for detection limit determination:

"The analytical sensitivity or detection limit for NAT assays shall be expressed by the 95 % positive cut-off value. This is the analyte concentration where 95 % of test runs give positive results following serial dilutions of an international reference material for example a WHO standard or calibrated reference materials."