Introduction

No international consensus exists on the methods for assessing diagnostic tests. Previous recommendations stress that studies of diagnostic tests should match the type of diagnostic question.1 2 Once the specificity and sensitivity of a test have been established, the final question is whether tested patients fare better than similar untested patients. This usually requires a randomised trial. Few tests are currently evaluated in this way. In this paper, we propose an architecture for research into diagnostic tests that parallels the established phases in drug research.

Stages of research

We have divided studies of diagnostic tests into four phases (box). We use research on brain natriuretic peptide for diagnosing heart failure as an illustrative example.2 However, the architecture is applicable to a wide range of tests including laboratory techniques, diagnostic imaging, pathology, evaluation of disability, electrodiagnostic tests, and endoscopy.

Establishing the normal range

In drug research, phase I studies deal with pharmacokinetics, pharmacodynamics, and safe doses.3 Phase I diagnostic studies are done to determine the range of results obtained with a newly developed test in healthy people. For example, after development of a test to measure brain natriuretic peptide in human plasma, phase I studies were done to establish the normal range of values in healthy participants.4 5

The harms and benefits of diagnostic tests needs evaluating—just as drugs do

Credit: GUSTO/SPL

Diagnostic phase I studies must be large enough to examine the potential influence of characteristics such as sex, age, time of day, physical activity, and exposure to drugs. The studies are relatively quick, cheap, and easy to conduct, but they may occasionally raise ethical problems—for example, finding abnormal results in an apparently healthy person.6 …