Systematic reviews of diagnostic tests

Systematic reviews are recent additions to the medical literature. In contrast to traditional narrative reviews, these reviews aim to answer a precisely defined clinical question and to do so in a way that is transparent and designed to minimize bias. Some of the defining features of systematic reviews are (1) a clear definition of the clinical question to be addressed, (2) an extensive and explicit strategy to find ail studies (published or unpublished) that may be eligible for inclusion in the review, (3) criteria by which studies are included and excluded, (4) a mechanism to assess the quahty of each study and, in some cases, (5) synthesis of results by use of statistical techniques of meta-analysis. By contrast, traditional reviews are subjective, are rarely well focused on a clinical question, lack explicit criteria for selection of studies to be reviewed, do not indicate criteria to assess the quality of included studies, and rarely can use meta-analysis. 

The explicit methodology of systematic reviews suggests that persons skilled in the art of systematic reviewing should be able to reproduce the data of a systematic review, just as researchers in chemistry or biochemistry expect to be able to reproduce published primary studies in their fields. This concept strengthens the credibility of systematic reviews, and workers in the field of EBM generally consider well-conducted systematic reviews of high-quality primary studies to constitute the highest level of evidence on a medical question. 

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Until recently, methodologists interested in systematic reviews have focused on studies of the effects of interventions, especially drugs, on patient outcomes. That work is generally applicable to systematic reviews of diagnostic tests that start with a question of the second type above. The opportunities to use the techniques, however, are limited as it is unusual to find more than one study on any combination of a test and an outcome. We therefore focus on systematic reviews of the diagnostic accuracy of tests and express the hope that the quality of primary studies will continue to improve so that many such systematic reviews will become feasible. 

Among the steps in conducting a systematic review of a diagnostic test (Box 13-1), the most important is the identification of the chnical question for which the test result is required to give an answer, and thus formulation of the question that forms the basis of the review. Two types of questions can be addressed in a systematic review in diagnostic medicine one type is related to the diagnostic accuracy of a test, and the other to the clinical value (to patients or to others) of using the test. The questions that arise are similar in structure but require different approaches. 

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Irwig L, Glasziou P. Cochrane Methods Group on Systematic Review of Screening and Diagnostic Tests recommended methods. Updated 6 June 1996. http //www.cochrane.org/cochrane/sadtdocl.htm (Accessed on March 15, 2003)... 

Rostom A, Dube C, Cranney A, Saloojee N, Sy R, Garritty C, et al. The diagnostic accuracy of serologic tests for celiac disease A systematic review. Gastroenterol 2005 128(4 Suppl 1) S38-S46. 

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