VALIDATION OF SEROLOGICAL ASSAYS FOR DIAGNOSIS OF INFECTIOUS-DISEASES

Assay validation is a series of the following interrelated processes: an experimental process: reagents and protocols are optimised by exper imentation to detect the analyte with accuracy and precision, and to e nsure repeatability and reproducibility in the assay a relative proces s: its diagnostic sensitivity and diagnostic specificity are calculate d relative to test results obtained from reference animal populations of known infection/exposure status a conditional process: classificati on of animals in the target population as infected or uninfected is co nditional upon how well the reference animal population used to valida te the assay represents the population to which the assay will be appl ied (accurate predictions of the infection status of animals from test results and predictive values of positive and negative test results a re conditional upon the estimated prevalence of disease/infection in t he target population) an incremental process: confidence in the validi ty of an assay increases over time when use confirms that it is robust as demonstrated by accurate and precise results (the assay may also a chieve increasing levels of validity as it is upgraded and extended by adding reference populations of known infection status) a continuous process: the assay remains valid only insofar as the assay continues t o provide accurate and precise results as proved through statistical v erification. Therefore, validation of diagnostic assays for infectious diseases does not end with a time-limited series of experiments based on a few reference samples. Rather, it is a process that also require s constant vigilance and maintenance, along with reassessment of its p erformance characteristics for each population of animals to which it is applied. It is certain that the current movement to develop and imp lement accreditation criteria for veterinary diagnostic laboratories m ay be of little worth unless there is some assurance that the assays c onducted in such laboratories are properly validated. Fully accredited laboratories may generate highly reproducible test results, but the r esults may still misclassify animals as to their infection status due to an improper assay validation process. Therefore, assay validation i s foundational to the core product of veterinary diagnostic laboratori es - test results and their interpretation.