Elevated levels of platelet microparticles are associated with disease activity in rheumatoid arthritis

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Abstract
Objective: Platelets are involved in various thrombotic events, often by means of platelet‐derived microparticles (PMPs). It is likely that platelets are also involved in inflammation. Because inflammatory processes play a central role in rheumatoid arthritis (RA), we sought to determine whether PMPs are present in this disease.Methods: This descriptive, cross‐sectional study included 19 RA patients and 10 healthy controls. Nine of the patients had active RA (erythrocyte sedimentation rate [ESR] ≥28 mm/hour and/or C‐reactive protein [CRP] level ≥28 mg/liter, ≥9 painful joints, and ≥6 swollen joints), and 10 had inactive disease (ESR ≤27 mm/hour, CRP ≤27 mg/liter, no tender joints, and no swollen joints). Platelet counts and PMP numbers were determined using cell counter and flow cytometry, respectively.Results: Platelet counts in the 3 groups were similar. However, levels of PMPs in RA patients were significantly higher than those in healthy controls (median 616 versus 118 × 106/liter; P = 0.005). PMP levels were higher in patients with active RA than in those with inactive RA (median 2,104 versus 504 × 106/liter; P > 0.05). Moreover, PMP levels correlated with disease activity (r = 0.67, P = 0.05).Conclusion: PMPs are associated with RA, and PMP levels are correlated with disease activity. Thus, platelets probably play a part in the inflammatory process of RA by means of PMPs. Given the importance of PMPs in cardiovascular diseases, this may be one reason for the enhanced cardiovascular morbidity and mortality in RA.