<p><b><i>Background:</i></b> Arteriovenous fistula (AVF) thrombosis is a relevant cause of morbidity in hemodialysis (HD) patients. The number of circulating endothelial progenitor cells (EPCs) has been identified as a surrogate marker for vascular repair and health. Deficiency of EPCs has been demonstrated in dialysis patients to be associated with vascular events. Nonetheless, their role in thrombosis of AVFs remains unknown. <b><i>Methods:</i></b> From January 2010 to May 2013, 147 HD patients with dysfunctional AVFs were enrolled. Surface makers including CD34, KDR and CD133 were used in combination to determine the number of circulating EPCs. All participants were prospectively followed at 6-month interval until December 2015. The primary outcome was thrombosis of dialysis AVFs. <b><i>Results:</i></b> The median follow-up was 47 months, within which 42 patients experienced at least one episode of AVF thrombosis. Patients with AVF thrombosis had lower CD34<sup>+</sup>KDR<sup>+</sup> cell counts compared with patients without thrombosis (median 5 vs. 13 per 150,000 mononuclear cells, p < 0.001). Kaplan-Meier analysis demonstrated an inverse relationship between CD34<sup>+</sup>KDR<sup>+</sup> cell count tertiles and thrombosis-free patency (59, 69 and 86% for low, middle and high tertiles; p = 0.02). Using Cox regression analysis, AVF thrombosis was predicted by baseline CD34<sup>+</sup>KDR<sup>+</sup> cell counts (hazards ratio (HR) 0.963, 95% CI 0.928-1.000, p = 0.05) and tertiles (high vs. low, HR 3.266, 95% CI 1.380-7.728, p < 0.01). In multivariate analysis, only CD34<sup>+</sup>KDR<sup>+</sup> cell tertiles, C-reactive protein and lesion length remained independent predictors for thrombosis. <b><i>Conclusion:</i></b> Our study demonstrated an independently reverse association between circulating EPCs and thrombosis of dialysis AVFs. Further studies are warranted to ascertain whether EPCs serve as a marker or a therapeutic target for AVF thrombosis.</p
