Recommendation for the unit of measurement and the measuring system to report traceable and comparable results expressing GM content in accordance with EU legislation

It is important to guarantee that results expressing the GM content are reliable, comparable and fulfil the requirements of existing EU legislation. The use of different measurement units to express a GM content, the appearance of new analytical methods that do not require a calibrant and the composite EU legislation on GMOs have triggered the need for a document to clarify how to obtain reliable and comparable results. For this guidance document, past and current EU legislations have been reviewed with a special emphasis on what is meant by 'GM percentage' in the different legal texts. The metrological traceability of measurement results and the currently available guidance are explained and summarised. The particular case of botanical impurities and the genetic constitution of GM seeds are described and illustrated to better understand the complexity hidden behind this type of analysis. An overview of the different analytical methods based on DNA measurements and used for the expression of quantitative GM content results is provided, including the use of new techniques based on digital PCR (dPCR). A measuring system that allows for comparing results by making them traceable to the same reference system has been elaborated in detail. Needs and tools are described and a solution has been proposed to convert results expressing GM content to the required measurement unit, whenever this is needed.