No conclusions could be made regarding other LMWHs because of limited data. Increased bleeding was also found in a post hoc analysis of data from the Ef cacy and Safety of Subcutaneous Enoxaparin in Non-Q-Wave Coro- nary Events (ESSENCE) and Thrombolysis in Myo- cardial Infarction (TIMI) 11B trials, in which CrCl  30 mL/min was associated with an increased risk for major hemorrhage in patients receiving ther- apeutic doses of enoxaparin (relative risk [RR]5 6.1; patients with either VTE or acute coronary ischemia treated with therapeutic doses of enoxaparin or tinza- parin, a CrCl , 20 mL/min was associated with a RR of 2.8 (95% CI, 1.0-7.8) for bleeding complica- tions.162 Finally, in a retrospective study of patients receiving multiple doses of enoxaparin, patients with renal insuf ciency had an RR for any bleeding com- plication of 2.3 (P,.01) and an RR for major hemor- In the setting of severe renal insuf ciency in which therapeutic anticoagulation is required, use of UFH avoids the problems associated with impaired clear- ance of LMWH preparations. Although there is no speci c CrCl threshold at which the risk for LMWH accumulation becomes clinically signi cant, an esti- mated CrCl of about 30 mL/min is a reasonable cutoff value based on the available literature. If LMWH is chosen for patients with an estimated cre- atinine clearance of,30 mL/min, anti-Xa monitoring LMWH in doses adjusted by total body weight.145 For thromboprophylaxis with xed-dose enoxaparin and nadroparin, there is a strong negative correlation between total body weight and anti-Xa levels in obese patients.146-148 Several small prospective trials have examined this issue in patients undergoing bariatric surgery, with inconclusive ndings.149-152 Appropriate dosing of LMWH in patients with severe renal insuf ciency is uncertain. 