Dear Guiseppe,
I agree that RCTs are not always needed for diagnostic tests. If we are
only concerned with the accuracy for the same spectrum of illness, then
accuracy studies are enough.
If you are changing the *spectrum* of disease detected and hence treated,
RCTs may be needed (for a subgroup). "Disease" is usually a continuum, and
treatment may not have net benefits at the lower risk/milder end of the
spectrum.
Regards,
Paul Glasziou
At 11/07/2005, Dr. Giuseppe Giocoli wrote:
>Dear List,
>
>About grading of diagnostic evidence in infectious diseases I wish to
>quote what KGM Moons and DE Grobbee wrote in their paper “Diagnostic
>studies as multivariable, prediction research. J Epidemiol Community
>Health 2002;56:337–338”:
>
>“We believe that evaluation of diagnostic tests on patient outcome is not
>always necessary. In general, we think that follow up studies are not
>necessary and the (beneficial) effect of a diagnostic test for patient
>outcome may be considered as established if (a) diagnostic (cross
>sectional) studies have shown the test’s ability to detect a particular
>disease and (b) therapeutic studies provided evidence on efficacy of the
>management of this disease”.
>
>If so, could a high-quality systematic review of cross-sectional accuracy
>studies represent the best grade of evidence - even in the absence of RCTs
>- when the tests’ purpose is identifying etiological agents of diseases,
>when clinical suspicion is medium-high?
>
>Perhaps I am not capturing the right meaning of Moons & Grobbee’s words,
>but I am tempted to think them appropriate in the following examples:
>
>Identification of microrganisms in the blood for endocarditis or in the
>CSF for meningitis, P.falciparum for suspected malaria, gonococcus or
>chlamydia for urethritis or cervicitis, and so on.
>
>On the other hand, it seems clear that in different situations a RCT is
>necessary to demonstrate the test usefulness.
>
>F:i.: screening low-prevalence populations for HIV or C.trachomatis or
>HSV-2, using rapid tests to instaurate empiric antibiotic therapies
>(cytokines for early diagnosis of sepsis in neonates or ELISA
>galactomannan for invasive aspergillosis), testing and treating syndromes
>not yet completely understood (H.pylori breath-test for peptic ulcer,
>bacterial vaginosis tests for pre-partum prophylaxis of adverse outcomes).
>
>Any comment?
>
>Thanks,
>
>Giuseppe
>
>Dr.Giuseppe Giocoli
>GdL EBM Associazione Microbiologi Clinici Italiani
>Via Sarca, 19
>25010 Desenzano d/G (BS)
>www.amcli.it
>
>
>
>Dr. Giuseppe Giocoli
>Via Sarca 19
>25015 Desenzano d/G (Italia)
Paul Glasziou
Department of Primary Health Care &
Director, Centre for Evidence-Based Practice, Oxford
ph: 44-1865-227055 www.cebm.net
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