Serum thrombopoietin levels in haemodialysis patients: involvement of arteriovenous fistula

Background. Thrombopoietin (Tpo) is a recently cloned growth factor which p lays a critical role in the regulation of thrombopoiesis. Tpo has also been shown to stimulate in vitro and in vivo erythroid cell growth. Although Tp s transcripts were detected in hepatocytes, proximal tubules and endotheliu m, mechanisms regulating the level of circulating Tpo have not been fully d elineated. Changes in the vessel wall and blood flow in arteriovenous fistu la (AVF)might alter Tpo activity. Methods. Serum thrombopoietin levels and serum erythropoietin levels in sam ples concurrently obtained from venous returns of AVF and contralateral per ipheral veins in 31 haemodialysis patients were determined and compared wit h 12 healthy controls. Levels were also compared between 14 haemodialysis p atients (group I) treated with recombinant human erythropoietin (rHu-Epo) a nd 17 haemodialysis patients (group II) not requiring rHu-Epo. Results. Serum Tpo levels (44.8 +/- 23.9 pg/ml, vs 129.9 +/- 113.6 pg/ml, P < 0.05) and platelet counts (194 +/- 55. 10(6)/ml vs 273 +/- 94. 10(6)/ml, P < 0.05) of haemodialysis patients were lower than healthy controls. Seru m Tpo levels were inversely correlated with platelet counts in the control group (R=-0.61, P < 0.05), but not in haemodialysis patients. Tpo concentra tions of AVF samples were lower than peripheral venous samples (31.6 +/- 17 .7 pg/ml vs 44.8 +/- 23.9 pg/ml, P=0.001). No significant difference was pr esent between the serum Tpo concentrations of haemodialysis patients in gro up I and group II. Serum Tpo levels were not correlated with haemoglobin le vels or serum erythropoietin levels in haemodialysis patients. Conclusion. Decreased serum Tpo levels despite low platelet counts in haemo dialysis patients suggest that the proposed feedback mechanism of platelet uptake of Tpo is not fully operative in these patients. Moreover, AVF might affect the local production and/or catabolism of this growth factor.