In the last section of the Bandolier paper on diagnostic testing, that was
kindly forwarded to us by Jonathan Kay, it is concluded: "Doing systematic
reviews of diagnostic tests is a complete waste of time".

As Mark Petticrew recently wrote in the British Medical Journal [1], the
high profile of systematic reviews (SRs) as a cornerstone of evidence based
medicine has led to several misconceptions about their purpose and methods.
Among these is the belief that SRs are applicable only to randomised
controlled trials and that they are incapable of dealing with other forms of
evidence [...]. The arguments which are commonly used to reject a wider role
for SRs are often based on major misconceptions about the history, purpose,
methods, and uses of SRs.

May we suggest to those who believe that "doing SRs of diagnostic tests is a
complete waste of time" to read Mark Petticrew's brilliant paper in which he
examines eight common myths about SRs [1]. In particular the section in
which Mark Petticrew examines the myth that SRs would necessarily involve
statistical synthesis. This particular myth derives from a misunderstanding
about the different methods used by SRs. Some reviews summarise the primary
studies by narratively describing their methods and results. Other reviews
take a statistical approach (meta-analysis) by converting the data from each
study into a common measurement scale and combining the studies
statistically. The above myth assumes that such reviews can only be done
this way. Many SRs, however, do not use meta-analytic methods. Some of those
which do, probably shouldn't; for example, it is common practice to pool
studies without taking into account variations in study quality, which can
bias the review's conclusions. It has been pointed out that one of the
allures of meta-analysis is that it gives an answer, no matter whether
studies are being combined meaningfully or not. SRs should not therefore be
seen as automatically involving statistical pooling as narrative synthesis
of the included studies is often more appropriate and sometimes all that is
possible.

The aim of doing SRs is not only to produce high quality evidence on a given
topic, but also to identify gaps in our knowledge and to highlight the need
for more well-designed research in the area of question. Also, systematic
reviewing in laboratory medicine is educational and critical appraisal
contributes to informed decision making. It also helps reviewers to design
better primary studies of diagnostic accuracy.

As a result, there are new standards for reporting studies of diagnostic
accuracy and details of the STARD project can be found on the CONSORT
website: http://www.consort-statement.org/. This will hopefully lead to
better quality primary diagnostic studies which will allow higher quality
systematic reviewing in the future.

Another initiative is the Bayes Library of diagnostic studies and reviews.
This database will contain prevalence data and a collection of likelihood
ratios of diagnostic tests, based on critical appraisal of the literature.
The aim of the database is to support diagnostic decisions, mainly in
primary care. The Bayes Library project has produced a methodology to
critical appraisal of the diagnostic literature and details of this project
will shortly be published elsewhere. For more details, please contact the
Committee on Evidence-based Laboratory Medicine at IFCC:
http://www.ifcc.org/ifcc.asp

In summary, we do not feel that SRs in diagnostics are a complete waste of
time, as previous attempts to SRs in this field, and methodological problems
identified throughout this process, have already contributed to checklists
of reporting primary studies (STARD project) and checklists of critical
appraisal of the diagnostic literature (the Bayes project). These
initiatives all aim at improving methodology of evidence-based diagnostics
and represent a learning curve towards better quality research in
diagnostics.

References:
[1] Petticrew M. Systematic reviews from astronomy to zoology: myths and
misconceptions BMJ 2001; 322:98-101 (13 January).

Prof. Andrea Rita Horvath and Dr. Joseph Watine, Committee on Evidence-Based
Laboratory Medicine of the International Federation of Clinical Chemistry
and Laboratory Medicine

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