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determine the status of the largest proportion of tested samples; they may or may not be equal in value and depending on the way the test is intended to be used, the cut- off value may be set differently. The prevalence of the disease being tested for in the population (Smith 2019) and the potential costs of misdiagnosis are other factors taken into account when setting a cut-off value. A screening assay needs a high diagnostic sensitivity. A confirmatory assay needs a high diagnostic specificity.
Analytical sensitivity, specificity and reliability Analytical sensitivity is an indication of the minimum detectable amount of the analyte for the test and can be a measure of the cross-reactivity with materials of no interest (Duart et al. 2014). Analytical specificity is an indication of the ability of a test to detect the pathogen in question over others, that is avoiding cross-reactivity from closely related pathogens. Reliability is a measure of the ability of a test to produce the same results when run multiple times. These factors should be established for each diagnostic test developed prior to widespread use.
Conclusion
In conclusion, infectious disease diagnostic testing choice and interpretation can appear to be complex, but there are a multitude of benefits from having a basic understanding of testing methods and their interpretation. Cases and outbreaks commonly require both agent detection and serological testing. Obtaining samples for agent detection at the correct time (when agent is present at site sampled, i.e. early on in course of disease) and just prior to instigating treatment enhances the chances of an accurate diagnosis. It is vital to utilise the test in conjunction with the specific case history (including vaccination status and reason for testing) and clinical signs. Overinterpreting test result’s exact numbers without relating them to the clinical scenario is an easy mistake to make. If a test result is unexpected, this should be acknowledged in partnership with the testing laboratory, as all diagnostic testing has the potential for incorrect results. Infectious diseases come with a plethora of politics and vets can feel pressurised in establishing or refuting disease diagnoses. Having a clear understanding of laboratory testing options and carrying out sampling in a thorough but efficient and timely manner will help to remove the stigma of infectious disease, and improve equine welfare and general content all round.
Authors’ declaration of interests No conflicts of interest have been declared.
Ethical animal research Not applicable to this review article.
Acknowledgements
Thanks to Toni-Ann Hammond, Kayleigh Hughes, Elizabeth Medcalf and Adam Rash formerly at the Animal Health Trust for their guidance and assistance in the production of this review.
Authorship
Both authors contributed to preparation of the manuscript and gave their final approval of the manuscript.
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