Elevated Monocytes in Patients with Critical Limb Ischemia Diminish after Bypass Surgery
Mononuclear cells (MNC) increase neovascularization and ulcer healing after injection into an ischemic extremity. Circulating MNC are composed of lymphocytes (85%), monocytes (15%) and endothelial progenitor cells (EPC; 0.03%). We hypothesized that ischemic limbs secrete paracrine signals to recruit bone marrow-derived monocytes and EPC into the circulation, such that patients with critical limb ischemia (CLI) have increased circulating monocytes compared to control patients. We also hypothesized that circulating monocytes and EPC recruitment decrease after resolution of ischemia with successful revascularization.
Methods: We reviewed the records of all patients at the VA Connecticut Healthcare System undergoing lower extremity peripheral bypass surgery between 2002 and 2007, only including patients with both preoperative and postoperative complete blood counts with differentials.
Results: Patients with CLI (n=24) had elevated preoperative monocyte counts compared to control patients (n=8) (0.753±0.04 vs. 0.516±0.05; p=0.0046), whereas the preoperative lymphocyte counts were not significantly different. After revascularization, ischemic patients had decreased monocyte counts compared to control patients (-20% vs. +55%; p=.0003), although lymphocyte counts were unchanged in both groups. Diabetic patients also had reduced postoperative monocyte counts (-32% vs. +13%; p=0.035). Multivariable logistic regression demonstrated that the only factor that independently predicted reduced postoperative monocyte count was preoperative CLI (p=0.038).
Conclusions: Patients with CLI have increased numbers of circulating monocytes, and the monocyte number decreases with resolution of ischemia after successful revascularization. Circulating monocytes may be a clinically useful perioperative marker in patients with CLI undergoing vascular surgery.
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