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Method validation involves a series of technical activities carried out with careful planning to identify the suitability of a test method for examining an identified matrix. The principles governing method validation are discussed in the section on chemical laboratories (Waitro\LabnetChemfiles\LabnetChemMtdsValida_files). Even a validated method has to be validated if changes were made to the procedure (diluents, test media, reagents, temperatures, or a combination of elements from different methods) or to the matrix. Non-validated methods and in-house methods need to be validated by a laboratory seeking accreditation for such methods. Before applying a testing method, the analyst needs to be confident that it works for the analyte and the matrix. This may take the form using spiked samples and comparing them against controls, blanks and closely related analytes. In microbiological testing, judgment of the identity of a microorganism must be based on all the documented features. For example, if a laboratory is using the morphological and biochemical characteristics of salmonella on Triple Sugar Iron Agar slants, it is important to have agreement on all the four parameters given in the table below to avoid misdiagnosis, since the microorganisms are closely related.
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