A philosophical perspective supports the need for patient-outcome studies in diagnostic test evaluation.

Objective: Most clinical research evaluates diagnostic tests by accuracy measures such as sensitivity and specificity. This is stimulated by the Standards for Reporting of Diagnostic Accuracy initiative, which focuses on accuracy in the widely accepted guidelines. Referring to the clinical consequences of diagnostic tests, many epidemiologists recognize the importance of patient outcome studies in addition to accuracy studies. However, there is a theoretical argument that stipulates the need for patient outcome studies, which has thus far been overlooked.

Results: Using a philosophical argument, we show that the definition of disease necessarily involves the concept of function, which in turn is inextricably related to outcome. Consequently, diagnostic tests that establish the presence or absence of disease cannot be evaluated without measuring patient outcome. Patient outcome studies are therefore the definitive means to assess the merits of a diagnostic test.

Conclusion: The need for patient outcome studies is not due to pragmatic reasons, as previous authors argued, but is based on a philosophical argument relating the definition of disease to the concept of function. We propose that authors justify the use of accuracy studies in papers reporting diagnostic test evaluation by describing the association between gold standard test and patient outcome.