Sensitivity, Specificity, and Predictive Value

Over the past decade, many clinicians have recognized the need to acquire an expanded clinical vocabulary and conceptual framework with which to interpret and act upon clinical information from the patient's history, the physical examination, and the diagnostic laboratory. This expanded vocabulary acknowledges the probabilistic nature of clinical events that occur consequent to diagnostic and therapeutic strategies and thereby provides clinicians with the tools for more meaningful communication with colleagues and patients. In essence, this approach addresses the uncertainty inherent in the information used to make diagnostic and therapeutic decisions, and its use permits a more explicit approach to making decisions concerning patient management.

As the medical student progresses through the clinical years and beyond, he or she undoubtedly will hear statements couched in the "old vocabulary." Statements such as "In our hands complications with this test are rare," "splenomegaly is often present in this disorder," and "if the exercise test is positive, then this patient most likely has coronary disease" are vague and leave room for variable interpretation. Terms such as "rare," "often," and "most likely" have different meanings for different listeners and therefore are limiting if one is attempting to communicate precisely. Perhaps students also will hear statements couched in the "new" clinical vocabulary. Statements such as "The risk of death from this procedure has been reported in several series to range from 1 to 5%," "splenomegaly is reportedly present in about 40 to 50% of patients with this disease," and "if the exercise test is positive, then I believe the patient has a 70 to 90% chance of having serious coronary artery disease" are used to replace the vague terminology. This chapter is an introduction to this new vocabulary using a clinical vignette about a patient with a common health problem, chest pain. We believe the concepts inherent in this expanded framework and vocabulary are useful tools in the everyday practice of medicine.