Diagnostic Accuracy Measures—The Laboratory and Non-Laboratory Perspective

For professionals in laboratory medicine, diagnostic accuracy is a term we think we understand well. Still, there are multiple and distinct interpretations of the term “diagnostic accuracy,” and laboratorians will benefit by improved understanding of them all. The clinical laboratory's understanding of diagnostic accuracy is the one we invoke daily and rely upon as the underpinning of our laboratory test results. Laboratorians often compare a new (index) test to a reference (gold) standard method to document the analytical performance of the test. Outside the laboratory walls, there is a broader definition, one that describes the ability of providers to accurately diagnosis a patient's illness. This definition relies not only on the accuracy of laboratory test results, but also on diagnostic radiology, diagnostic respiratory testing, the assessment of clinical symptoms, and the use of severity scores. To better understand diagnostic accuracy, one can divide its use into three broad categories: analytical validity (the aspect best known by clinical laboratories), clinical validity (the aspect that is best known to health care providers, and clinical utility (the aspect best known to policymakers and insurance providers). This review describes the term “diagnostic accuracy” as it is used in laboratory medicine and clinical medicine. Basic definitions and characteristics of the conventional measures of diagnostic accuracy are described and compared. Diagnostic accuracy in terms of clinical utility is discussed briefly, but a full discussion is beyond the scope of this review.