The architecture of diagnostic research

doi:10.1136/bmj.324.7336.539

From trainee to consultant, BMJ Group offers doctors around the world tailored information, special events, learning resources and recruitment services at every step along their career path.

... by doctors, for doctors, for patients
We are open for entries!

Online learning

BMJ Learning

High-quality CME / CPD for doctors and other healthcare professionals. BMJ Learning features hundreds of accredited, peer-reviewed learning modules in text, video, and audio formats. Find out more

Courses and Qualifications

BMJ Masterclasses

BMJ Masterclasses, led by experts, help clinicians to use the latest evidence and recent guidelines in practice and meet their CPD/CME requirements. Find out more

Exam Preparation

The leading provider of online exam preparation, helping over 167,000 healthcare professionals to pass their exams. Find out more

onExamination

Search all BMJ education articles:

From

Limit by

Access to the full text of this article requires a subscription or payment. Please log in or subscribe below.

D L Sackett, professor (sackett@bmts.com)a,
R B Haynes, directorb

^a Trout Research and Education Centre at Irish Lake, RR1, Markdale, ON, Canada N0C 1H0
^b Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada L8N 3Z5

Correspondence to: D L Sackett

This is the second in a series of five articles

Considerable effort has been expended at the interface between clinical medicine and scientific methods to achieve the maximum validity and usefulness of diagnostic tests. This article focuses on the specific kinds of questions that arise in diagnostic research and the study architectures (the conversions of these clinical questions into appropriate research designs) used to answer them. As an example we shall take shall take assessment of the value of the plasma concentration of B-type natriuretic peptide (BNP) in the diagnosis of left ventricular dysfunction.1 Randomised controlled trials are dealt with elsewhere.

As in other forms of clinical research, there are several different ways studying the potential or real diagnostic value of a physical sign or laboratory test, and each is appropriate to one kind of question and inappropriate for others. Among the possible questions about the relation between a putative diagnostic test and a target disorder (for example, the concentration of BNP and left ventricular dysfunction), four are most relevant.

Summary points

Diagnostic studies should match methods to diagnostic questions

Do test results in affected patients differ from those in normal individuals?
Are patients with certain test results more likely to have the target disorder?
Do test results distinguish patients with and without the target disorder among those in whom it is clinically sensible to suspect the disorder?
Do patients undergoing the diagnostic test fare better than similar untested patients?

The keys to validity in diagnostic test studies are

independent, blind comparison of test results with a reference standard among a consecutive series of patients suspected (but not known) to have the target disorder
inclusion of missing and indeterminate results
replication of studies in other settings

Both specificity and sensitivity may change as the same diagnostic test is applied in primary, …