Principles and Methods of Validation of Diagnostic Assays for Infectious Diseases

Validation is a process that determines the fitness of an assay, which has been properly developed, optimised and standardised, for an intended purpose. Validation includes estimates of the analytical and diagnostic performance characteristics of a test. In the context of this chapter, an assay that has completed the first three stages of the validation pathway (see Figure 1 below), including performance characterisation, can be designated as “validated for the original intended purpose(s)”1. To maintain a validated assay status, however, it is necessary to carefully monitor the assay’s daily performance, often by tracking the behaviour of internal controls over time. This ensures that the assay, as originally validated, consistently maintains its performance characteristics. Should it no longer produce results consistent with the original validation data, the assay may be rendered unfit for its intended purpose. Thus, a validated assay is continuously assessed to assure it maintains its fitness for purpose through assessment of results of internal controls in each run of the assay.