The aims of this study were to determine the serum antifactor Xa levels in patients with impaired glomerular filtration receiving low-molecular-weight heparins (LMWHs), monitor efficacy and complications during treatment, and determine the approach to dose adjustments of LMWH by using antifactor Xa levels in different levels of kidney dysfunction in a real world clinical practice. Patients with chronic kidney disease who had subcutaneous enoxaparin administration during hospitalization were included in this study. We obtained data on patient demographics, glomerular filtration rate, bleeding complications, and antifactor Xa levels. Patients were divided into four groups based on glomerular filtration rate (>60 ml/min, 30-59 ml/min, 15-29 ml/min, <15 ml/min). Target levels for antifactor Xa were accepted as 0.1-0.4 IU/ml for prophylactic use and 0.4-1.1 IU/ml for therapeutic use. There were 61 patients and 18 controls (40 women, 39 men, mean age 68+/-12 years) available for analysis. Interpretation of antifactor Xa with regard to target levels has shown that levels were in therapeutic range in 33 patients (41.8%), subtherapeutic range in 38 patients (48.1%), and supratherapeutic range in eight patients (10.1%). Less than half of the patients at each level of kidney dysfunction had antifactor Xa levels within the therapeutic range. Three patients suffered major bleeding, two with supratherapeutic, and one with therapeutic antifactor Xa level. There were no complications of ineffective anticoagulation in patients with subtherapeutic levels. Inappropriate dosing of LMWH suggested by subtherapeutic and supratherapeutic antifactor Xa levels were very high in patients with different levels of kidney dysfunction. Blood Coagul Fibrinolysis 23: 700-704 (C) 2012 Wolters Kluwer Health vertical bar Lippincott Williams & Wilkins.