Systematic reviews in laboratory medicine: principles, processes and practical considerations.

BACKGROUND Systematic reviews and meta-analyses are generally accepted to represent the highest level of evidence, and are a cornerstone in practising evidence-based medicine. So far, these efforts have been largely confined to the evaluation of the efficacy and effectiveness of therapeutic and preventive interventions. Systematic reviews in laboratory medicine are scarce and many of them do not meet essential quality criteria [Clin. Chem. Lab. Med. 38 (2000) 577]. Most of these problems are related to the poor design and heterogeneity of primary research, and that there are no agreed methods or quality standards for making systematic reviews in laboratory medicine. AIMS AND OBJECTIVES For better evidence in laboratory medicine, not only higher quality primary studies but also standardized methodologies for designing, conducting and reporting systematic reviews in diagnostics are needed. The aim of this review is to present the general principles and provide a step-by-step process of systematic reviewing in laboratory medicine. METHODS This narrative review is based on the overview of the medical literature on the methodology of systematic reviewing and that of the "state of the art" of evidence-based diagnosis. RESULTS Systematic reviews of diagnostic interventions differ from that of therapeutic interventions in the methods of question formulation, the choice of study design, the assessment of study quality and the statistical methods used to combine results. Therefore, the general principles of systematic reviewing are adapted to the specialist field of laboratory medicine. The process of systematic reviewing consists of six key steps: (1) preparation for the review, (2) systematic search of the primary literature, (3) selection of papers for review, (4) critical appraisal of the selected literature, (5) analysis and synthesis of data, and (6) interpretation of data. The most important technical and methodological aspects of each step and the essential elements of a good systematic review in laboratory medicine are presented. CONCLUSIONS Systematic reviews of diagnostic interventions support clinical and policy decisions, the development of practice guidelines, clinical audit, technology assessment, economic evaluations, education and training, and identify gaps in our knowledge for future research. Systematic reviewing of laboratory data is expected to result in better, bigger and more reliable primary studies, which hopefully will support the diffusion of new diagnostic technologies with scientifically proven efficacy and effectiveness in the future.