Platelet hyperactivity in clinical depression and the beneficial effect of antidepressant drug treatment: how strong is the evidence?

OBJECTIVE: Platelet hyperactivity is thought to contribute to the increased coronary artery disease (CAD) risk in depression. This study reviewed the evidence for hyperactive platelets and for effects of antidepressant drug treatment on platelet 'stickiness' in clinical depression. METHOD: By means of PubMed electronic library search, 34 studies in English were identified (1983-2003) and critically reviewed. RESULTS: In depression, flow cytometry studies allowing detection of subtle platelet activation states consistently found at least one platelet activation marker to be increased, while the bulk of platelet aggregation studies did not suggest increased platelet aggregability. Platelets seem to be more activated in depressed patients with CAD than in depressed individuals without CAD. The selective serotonin reuptake inhibitors normalized platelet hyperactivity in four studies. CONCLUSION: Data on platelet activity in depression are inconclusive. To resolve this issue and its clinical implications, studies in larger sample sizes controlling for confounders of platelet functioning and prospectively designed are needed.