Objectives: explaining how diagnostic test performanceisassessed,whetherusedforscreening or confirming a certain disease, and explaining how a diagnostic test’s operational characteristics are used for reducing uncertainty about the absence or presence of the disease for which it is being used. Methodology: the main concepts underlying the assessment of the performance, validity, interpretation and the use of screening and diagnostic tests' operational characteristics are addressed within a clinical context. A sample clinical scenario is then resolved using the tools provided for the reader. Results: the natural history of disease, a definition of normality, percentages and ratios are essential concepts for the proper use and interpretation of a screening or a diagnostic test's operational characteristics. Knowledge of pre-test probability and positive and negative likelihood ratios for a test being used is necessary for reducing uncertainty in a given diagnostic process. Conclusions: interpreting a given diagnostic test's operational characteristics determines its optimal use for screening or accurately ruling out disease and thereby solving the problems we face daily in our clinical practice.
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