Evaluation of diagnostic procedures

doi:10.1136/bmj.324.7335.477

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J André Knottnerus, professor of general practice (andre.knottnerus@hag.unimaas.nl)a,
Chris van Weel, professor of general practiceb,
Jean W M Muris, senior lecturer in general practicec

^a Netherlands School of Primary Care Research, PO Box 616, 6200 MD Maastricht, Netherlands
^b Department of General Practice, University Medical Centre St Raboud, 6500 HB Nijmegen, Netherlands
^c Department of General Practice, Maastricht University, 6200 MD Maastricht, Netherlands

Correspondence to: J A Knottnerus

This is the first of a series of five articles

Development and introduction of new diagnostic techniques have greatly accelerated over the past decades. The evaluation of diagnostic techniques, however, is less advanced than that of treatments. Unlike with drugs, there are generally no formal requirements for adoption of diagnostic tests in routine care. In spite of important contributions, 1 2 the methodology of diagnostic research is poorly defined compared with study designs on treatment effectiveness, or on aetiology, so it is not surprising that methodological flaws are common in diagnostic studies.3^–5 Furthermore, research funds rarely cover diagnostic research starting from symptoms or tests.

Since quality of the diagnostic process largely determines quality of care, overcoming deficiencies in standards, methodology, and funding deserves high priority. This article summarises objectives of diagnostic testing and research, methodological challenges, and options for design of studies.

Summary points

Development of diagnostic techniques has greatly accelerated but the methodology of diagnostic research lags far behind that for evaluating treatments

Objectives of diagnostic investigations include detection or exclusion of disease; contributing to management; assessment of prognosis; monitoring clinical course; and measurement of general health or fitness

Methodological challenges include the “gold standard” problem; spectrum and selection biases; “soft” measures (subjective phenomena); observer variability and bias; complex relations; clinical impact; sample size; and rapid progress of knowledge

Objectives of testing

Diagnostic investigations collect information to clarify patients' health status, using personal characteristics, symptoms, signs, history, physical examination, laboratory tests, and additional facilities. Objectives include the following.

Increasing certainty of the presence or absence of disease—This requires sufficient discriminative power. Measures of discrimination are commonly derived from a 2×2 table relating test outcome to a reference standard (figure), thus allowing tests to be compared. Tests for similar purposes may vary in accuracy, invasiveness, and risk, and, for example, history …