Head-to-head prospective RCT data for NO- ACs are needed for further evaluation of comparative bleeding risk and effectiveness. Commercial assays to measure NOAC serum levels are now available, but reference ranges derived from published literature are variable and are not well cor- related with safety, efficacy, and clinical outcomes. Indi- cations for measurement of NOAC serum levels might include: Measurement of drug levels in patients undergo- ing urgent surgical procedures. Uncovering accumulation of potentially toxic drug levels in patients with CKD or those undergoing dialysis. Detection of potential drug drug interactions to guide dose adjustment. Evaluation of drug absorption in severely obese patients (body mass index >35 or weight >120 kg) Assessment of patient adherence. 4.3. Interruption and Bridging Anticoagulation Recommendations for Interruption and Bridging Anticoagulation Referenced studies that support new or modified recommendations are summarized in Online Data Supplement 3. COR LOE Recommendations I C Bridging therapy with unfractionated heparin or low-molecular-weight heparin is recommended for patients with AF and a mechanical heart valve undergoing procedures that require interruption of warfarin. Decisions on bridging therapy should balance the risks of stroke and bleeding. I B-R For patients with AF without mechanical heart valves who require interruption of warfarin for procedures, decisions about bridging therapy (unfractionated heparin or low-molecular-weight heparin) should balance the risks of stroke and bleeding and the duration of time a patient will not be MODIFIED: LOE was updated from C to B-R because of new evidence. (Section 4.1. in the 2014 AF Guideline) I B-NR Idarucizumab is recommended for the reversal of dabigatran in the event of life-threatening bleeding or an urgent NEW: New evidence has been published about idarucizumab to support LOE B-NR. 