ContextIndividuals with cardiovascular disease (CVD) are at high risk for further cardiovascular events. Further risk stratifi cation in these individuals could allow more precise targeting of invasive tests (eg, cardiac stress tests, angiograms) as well as interventions (blood pressure or lipid lowering, antithrombotics, revascularisation, etc) aiming to reduce subsequent risk but which also confer risk, inconvenience and costs to the individual and/or the healthcare system. Better methods of risk stratifi cation are therefore of great interest.C reactive protein (CRP) is an infl ammatory marker associated with risk in people without CVD. 1 The review by Hemingway and colleagues aimed to consolidate the available evidence assessing CRP as a risk marker in people with coronary artery disease and to assess whether there was evidence of bias affecting the results.
MethodsThis study is a systematic review of prospective observational studies reporting the association between CRP and death or CVD identifi ed from Medline and Embase. Studies were selected if participants had stable coronary artery disease, and were excluded if they measured CRP during admissions for acute coronary syndromes or revascularisation, as assessed by three reviewers. The outcomes assessed were clearly defi ned: coronary events, cardiovascular events and death. A random effects meta-analysis was performed, with additional sensitivity analyses to identify biases potentially affecting the results. Interestingly, the authors did not refer to the MOOSE guidelines 2 for systematic reviews of observational studies, although they were mostly followed.
FindingsEighty-three studies including information on 6485 events among 61 485 patients were identifi ed, most of which did poorly on quality assessment. Overall, individuals in the top third of the CRP distribution had double the risk of an event compared with those in the lower third (HR 1.97, 95% CI 1.78 to 2.17), but there was evidence of considerable heterogeneity between studies (I 2 =79.5) and publication bias (Egger's test, p=0.001). Only 13 studies adjusted for conventional risk factors and the pooled estimate from those was 1.65 (95% CI 1.39 to 1.96). In some models adjusting for publication bias, the relationship was no longer statistically signifi cant. These fi ndings strongly support the notion that any true relationship between CRP and the risk of adverse outcomes in people with stable coronary disease has been overstated, and the value of measuring CRP in this population remains to be proven. Commentary on: Hemingway H, Philipson P, Chen R, et al. Evaluating the quality of research into a single prognostic biomarker: a systematic review and meta-analysis of 83 studies of C-Reactive protein in stable coronary artery disease. PLoS Med 2010;7:e1000286.