Protein produced by B lymphocytes in response to a foreign molecule or invading organism (Alberts B, Bray D, Lewis J, Raff M, Roberts K, Watson JD. Molecular Biology of the Cell. 3rd edn. New York, NY: W. W. Norton & Company; 1994).

The lowest and highest values within which an assay can detect and quantify the target entity. There will be evidence of acceptable reliability and validity of the test within this range. [Cox KL, Devanarayan V, Kriauciunas A, Manetta J, Montrose C, Sittampalam S. Immunoassay Methods. In Sittampalam GS, Grossman A, Brimacombe K, et al., editors. Assay Guidance Manual. Bethesda, MD: Eli Lilly & Company and the National Center for Advancing Translational Sciences; 2019. URL: www.ncbi.nlm.nih.gov/books/NBK92434/ (accessed July 2020).]

In the case of two (or more) drugs with identical active ingredients, similar bioavailability, equivalent physiological activity and, thus, interchangeability. Biosimilar drugs demonstrate bioequivalence to an originator product. See Bioequivalence [World Health Organization. Key Resources. URL: https://extranet.who.int/prequal/content/bioequivalence-0 (accessed August 2019).]

A biological medicine that is highly similar to another biological medicine already licensed for use. It is a biological medicine that has been shown not to have any clinically meaningful differences from the originator biological medicine in terms of quality, safety and efficacy [NHS England and NHS Improvement. What is a Biosimilar Medicine? URL: www.england.nhs.uk/publication/what-is-a-biosimilar-medicine/ (accessed August 2019).]

The name given to a pharmaceutical product by the manufacturer; for example, Valium is the originator brand name (also called trade name) for diazepam. The use of this name is reserved exclusively to its owner, in contrast to the generic name, which is diazepam. Brand names may also be used for generic products: they are then often called ‘branded generics’. These brand names are different from innovator brand names. [World Health Organization. Generic medicines. WHO Drug Information 2016;30:370–5. URL: www.who.int/medicines/publications/druginformation/WHO_DI_30-3_GenericMedicines.pdf?ua=1 (accessed August 2019).]