• Ioanna Tzoulaki, Konstantinos C M Siontis, and John P A Ioannidis.
• Department of Hygiene and Epidemiology, University of Ioannina School of Medicine, Ioannina, Greece.
• BMJ. 2011 Jan 1; 343: d6829.

ObjectiveTo compare the reported effect sizes of cardiovascular biomarkers in datasets from observational studies with those in datasets from randomised controlled trials.DesignReview of meta-analyses.Study SelectionMeta-analyses of emerging cardiovascular biomarkers (not part of the Framingham risk score) that included datasets from at least one observational study and at least one randomised controlled trial were identified through Medline (last update, January 2011).Data ExtractionStudy-specific risk ratios were extracted from all identified meta-analyses and synthesised with random effects for (a) all studies, and (b) separately for observational and for randomised controlled trial populations for comparison.Results31 eligible meta-analyses were identified. For seven major biomarkers (C reactive protein, non-HDL cholesterol, lipoprotein(a), post-load glucose, fibrinogen, B-type natriuretic peptide, and troponins), the prognostic effect was significantly stronger in datasets from observational studies than in datasets from randomised controlled trials. For five of the biomarkers the effect was less than half as strong in the randomised controlled trial datasets. Across all 31 meta-analyses, on average datasets from observational studies suggested larger prognostic effects than those from randomised controlled trials; from a random effects meta-analysis, the estimated average difference in the effect size was 24% (95% CI 7% to 40%) of the overall biomarker effect.ConclusionsCardiovascular biomarkers often have less promising results in the evidence derived from randomised controlled trials than from observational studies.

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