How to request a test: A clinician's guide to the interpretation and evaluation of medical tests

Abstract How to Request a Test: A Clinician’s Guide to the Interpretation and Evaluation of Medical Tests is a comprehensive overview of everything a doctor needs to know before performing a test. It fast-tracks learners to the level of experienced clinicians by providing insight into how they are able to use minimal tests to rapidly arrive at diagnoses. Illustrated throughout with real-life examples from multiple medical and surgical specialties, it begins with a simple definition of a test before moving on to explain the pros and cons of simple terms used to describe diagnostic accuracy, such as sensitivity, specificity, and predictive values. It continues with an introduction to Bayes’ theorem and explains how likelihood ratios are a possible solution to the drawbacks of simple measures of diagnostic accuracy. In light of this, the book evaluates the controversial case of prostate cancer screening with prostate-specific antigen. Drawing on classic papers from the 1970s, the book then introduces basic medical decision theory based on threshold values and explains their practicality in real-world scenarios. The book then turns from an individual to a public health approach, describing different methods of evaluating tests before they are introduced into healthcare systems, including the use of randomized controlled trials to determine their impact on patient outcomes. The example of a novel test for tuberculosis is used to illustrate how this works in practice and the book concludes with a simple four-point checklist for clinicians to consider before requesting a test.