Positive controls for IVD molecular assays are available in a range of formats and can be used to assess different steps within an MDx assay process (e.g. extraction, reagent performance, PCR cycling). In general, control material that most closely imitates a real target, in all features, will give the most complete validation. One of the more commonly used controls in qPCR/RT-qPCR assay for pathogen detection are extraction controls that are used in parallel to test specimens. Traditionally these have been variations of the target, for example, chemically inactivated virus or bacteria. However new artificial forms, such as assay-specific target nucleic acids artificially encapsulated in something similar to a live organism (virus like particle (VLP)), are frequently sought out due to their easiness to handle and stability.
Regardless of the format used, a positive extraction control signal validates the extraction processes and all downstream steps (amplification, detection, etc.). If an assay workflow is designed appropriately, it is now possible to combine the functions of extraction controls and process controls within a single control.