After indirect comparison of the available evidence from separate studies, it appears that adjusting the LMWH dose based on monitoring anti factor Xa concentrations for patients with renal dysfunction was associated with reduced risk of developing major bleeding (RR, 0.12 [95% CI, 0.03-0.44]; ARR, 95 fewer episodes per 1000 [95% CI, 60 fewer to 104 fewer episodes per 1000]; very low certainty). In an analysis of observational studies not included in the measured peak enoxaparin anti factor Xa concentrations were found to be within the defined therapeutic range.86,88,90,93-95 In 100.0%]) measured tinzaparin anti factor Xa concentrations fell within the defined therapeutic range.91 It was difficult to put these results into perspective given the lack of a control group where LMWH doses were not adjusted based on anti factor Xa concentrations. Harms and burden. Given the limited information regarding potential undesirable effects associated with adjusting LMWH doses based on the results of anti factor Xa monitoring that was available, the panel determined that the balance between desirable and undesirable effects of this intervention is very uncertain. Other EtD criteria and considerations. The panel agreed that there would likely be moderate costs associated with measuring anti factor Xa concentrations; cost-effectiveness remains unclear. Many payers would not consider this in- tervention acceptable without convincing evidence of benefit, and this evidence is lacking. The feasibility of implementing this intervention may also be affected by the following barriers reported by observational studies: (1) anti factor Xa tests are not widely available97 ; (2) anti factor Xa tests are poorly standardized between laboratories, making proper LMWH dose adjustments impossible in some cases97 ; and (3) anti factor Xa test reproducibility is poor.98-100 Conclusions and research needs for this recommendation. 