This WHO document provides practical guidance on the preparation of secondary biological reference materials and on their calibration to WHO International Standards (IS) where available. The document focuses on the in vitro measurement procedures used for diagnosis, detection and management of infectious diseases where the typical analytes (measurands) are nucleic acid or antigen (Ag). These IVD tests cover nucleic acid amplification technique (NAT)-based assays for detecting the DNA or RNA of infectious agents and immunological tests for the detection of Ag(s) of infectious agents. Currently, there are only a small number of IS with an assigned unitage available where the analyte is an antibody directed to an infectious agent. Due to their complexity (that is, the epitope spectrum represented by polyclonal antibodies in the serum  of a patient) this document does not cover antibody-based secondary standards. However, several principles outlined in this manual may also apply to antibody assays. Where applicable, the document integrates existing guidance, referenced accordingly.

The document is intended for use by manufacturers of secondary reference materials, IVD manufacturers, providers of EQA or PT programmes and other laboratories using reference materials for NAT-based and serological infectious disease assays. Analogous guidance has already been issued by WHO on secondary standards for vaccines and chemical reference substances.