International Normalized Ratio measurement during perioperative anticoagulation bridging with Low Molecular Weight Heparin in patients undergoing heart valve replacement surgery

Abstract

BackgroundSurgical procedures in anticoagulated patients require specific attention due to increased bleeding risk. Preoperative anticoagulation interruption in high-risk patients is often necessary. Bridging anticoagulation with low-molecular-weight heparin (LMWH) minimizes thromboembolic risk, but its effect on INR measurement is not well established, necessitating careful monitoring and individual assessment. ObjectivesInvestigating the effect of heparin bridging on INR measurements in anticoagulated patients on vitamin K antagonist (VKA) and by in vitro spiking experiments. Methods38 anticoagulated patients on VKA undergoing valve replacement surgery were studied using two plasma-based INR assays and one whole blood point-of-care INR method on multiple timepoints after postoperatively resuming VKA. Furthermore, we compared INR levels in pooled plasma of both normal and VKA-treated individuals, with seven spiked concentrations of LMWH or unfractionated heparin (UFH) in four INR assays. ResultsIn LMWH-bridged anticoagulated patients, the INR results obtained with HemosIL® RecombiPlasTin® and point-of-care Coaguchek are significantly higher compared to STA® Hepato Prest, within 3 days after restart of VKA. After spiking of LMWH or UFH in various concentrations into pooled plasma, only STA® Hepato Prest assay shows no interference in INR measurement within the therapeutic range (1.0-2.0 international units/mL) in both VKA and normal plasma. All other assays have substantial interference, with the Thromborel® S assay being the most heparin-sensitive assay. ConclusionDifferences between INR methods are seen within 72 hours after restarting VKA in post-operative patients who receive LMWH-bridging. In vitro experiments using LMWH and UFH show the interference of heparin in multiple INR methods, even with concentrations below suppliers-stated heparin interference limits.