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Target-specific DISCRIMINATION/IDENTIFICATION principle: t

According to Etymology Online,[3] the verb assay, at least since the 13th century, meant “to try, endeavor, strive; test the quality of”, from Anglo-French assaier, from assai (n.), from Old French essai “trial”, and the noun assay thus means “trial, test of quality, test of character”, mid-14th century, from Anglo-French assai and the meaning “analysis” is from the late 14th century. For assay of currency coins, this literally meant analysis of the purity of the gold or silver or whatever precious component was used to represent the true value of the coin. This might have translated later (possibly after the 14th century) into a generalized meaning of analysis,[citation needed] e.g. of an important or principal component of a target inside a mixture such as an active ingredient of a drug inside the inert excipients in a pharmacological formulation which originally used to be measured by its actual action on an organism (e.g. lethal dose or inhibitory dose).

An assay (analysis) is never an isolated process and must be combined with pre- and post-analytic procedures. The information communication (e.g. request to perform an assay and further information processing) or specimen handling (e.g. collection, transport and processing) that are done until the beginning of an assay are the preanalytic steps. Similarly, after the assay, the result may be documented, verified and transmitted/communicated in steps that are called post-analytic steps. Like any multi-step information handling and transmission systems, variation and errors in the communicated final results of an assay involve corresponding parts in every such step; i.e. not only analytic variations and errors intrinsic to the assay itself but also variations and errors involved in preanalytic and post analytic steps. Since the assay itself (the analytic step) gets much attention,[4] steps that get less attention by the chain of users, i.e. the preanalytic and the post analytic steps, are often less stringently regulated and generally more prone to errors – e.g. preanalytic steps in medical laboratory assays may contribute to 32–75% of all lab errors.[5]