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Relationships between platelets and inflammatory markers in rheumatoid arthritis

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Abstract

Aim of the study: To investigate platelets and different inflammatory markers in conjunction with a substantial inflammatory reaction. We used individuals with active rheumatoid arthritis (RA) as an experimental cohort. Methods: We selected 16 patients with active RA having at least one affected joint. On day 1, platelet and neutrophil counts together with C-reactive protein (CRP) were determined. We further analysed platelet volume (MPV) and plasma levels of thrombopoietin (TPO), P-selectin, myeloperoxidase and interleukin 6 (IL-6). After 2 years when all patients failed to show any swollen joints all analyses were repeated. Results and conclusions: As expected platelet count, CRP and IL-6 were elevated in active RA. The measures correlated with each other thus reflecting the same characteristic of the inflammatory response. The neutrophil count, MPV and myeloperoxidase also mirror disease activity. They failed to correlate with other activity markers thus providing unique information. MPV and myeloperoxidase on day 1 correlated with recovery values. Therefore, they could be suitable to use when following the inflammatory reaction over a long period of time.

Introduction

Platelet count [1], C-reactive protein (CRP) and neutrophil count are markers reflecting the inflammatory response. Thrombopoietin (TPO) increases number, ploidy and size of megakaryocytes [2]. Upon activation P-selectin is moved to the surface of platelets and endothelial cells and acts as a receptor for neutrophils [3]. In contrast, circulating P-selectin limits inflammatory reactions [4]. Myeloperoxidase reflects neutrophil activity [5]. Interleukin 6 (IL-6) promotes the synthesis of CRP. It also stimulates megakaryocytes and correlates with the degree of thrombocytosis [6]. This study compares the abovementioned measures reflecting the inflammatory response. Active rheumatoid arthritis (RA) was selected as an experimental model.

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Material and methods

RA-patients (n=16) with inflammatory signs in one or multiple joints participated. After 2 years all subjects had quiescent disease, i.e. no swollen joints as indicated by a telephone interview. The criteria of the American Rheumatism Association were used for diagnosis. The subjects were predominantly females (n=12) and aged 63±10 (S.D.) years (Table 1). All patients with one exception were rheumatoid factor positive. The study group had more corticosteroids (p<0.01) and less methotrexate (p

Results

As expected at active RA platelet count (p=0.01), CRP (p<0.05) and neutrophils (p<0.01) were elevated (Table 2). Furthermore, MPV (p<0.01), myeloperoxidase (p<0.001) and IL-6 (p<0.05) were enhanced. Moreover, the hierarchies of MPV (r=0.8; p<0.001), TPO (r=0.9; p<0.001), soluble P-selectin (r=0.6; p<0.05) and myeloperoxidase (r=0.9; p<0.001) were maintained during recovery (Table 2). Table 3 reveals that the platelet count at active disease correlated with CRP (r=0.7; p<0.01) and IL-6 (r=0.7; p

Discussion

The present study aims to investigate relationships between platelets and inflammatory parameters in conjunction with a substantial inflammatory reaction. We studied RA patients having at least one swollen joint. As expected platelet count, CRP and IL-6 were elevated reflecting the same feature of the inflammatory response. Neutrophils, MPV and circulating myeloperoxidase were also enhanced. They did not correlate with other measures thus providing unique information. MPV and myeloperoxidase

Acknowledgments

This work was supported by grants from the Curt Groschinsky Foundation, the Signe and Reinholds Sunds Foundation, the Vrinnevi Hospital Research Board and from the Östergötland County Council.

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