Results also suggested the possibility of increased risk of major bleeding, but again, the CI includes no difference and a very large increase in bleeding (RR, 3.91 [95% CI, 0.67-22.95]; ARR, 30 more episodes per 1000 [95% CI, 3 fewer to 227 more episodes per 1000]; very low confidence). Other EtD criteria and considerations. The panel de- termined that there would likely be moderate costs associated with measuring anti factor Xa concentrations, but the actual cost- effectiveness of this intervention could not be estimated due to the lack of comparative studies. Some payers would not consider this intervention acceptable without convincing evidence of benefit, and this evidence is currently 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 (2) Anti factor Xa tests are poorly standardized between laboratories, making proper LMWH dose adjustments impossible in some cases.97 (3) Anti factor Xa test reproducibility Thus, whereas it is feasible to order and obtain the results of anti factor Xa tests for patients with obesity during LMWH therapy in some settings, the panel determined that poor anti factor Xa test standardization and reproducibility were significant issues arguing against adjusting LMWH doses based on results of these tests. Conclusions and research needs for this recommendation. The guideline panel determined that there is very low certainty evidence for net harm from adjusting LMWH doses based on anti factor Xa concentration monitoring over no such monitor- ing for patients with obesity on LMWH therapy for treatment of VTE. In addition, there were concerns relating to anti factor Xa test standardization and reproducibility, weak correlation be- tween bleeding events and anti factor Xa concentrations,101 and no evidence that anti factor Xa testing is needed for patients with obesity. 