International normalized ratio measurement during perioperative anticoagulation bridging with low-molecular-weight heparin in patients undergoing heart valve replacement surgery.

Background: Surgical 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 international normalized ratio (INR) measurement is not well established, necessitating careful monitoring and individual assessment.

Objectives: To investigate the effect of heparin bridging on INR measurements in anticoagulated patients on vitamin K antagonist (VKA) and in spiking experiments.

Methods: Thirty-eight anticoagulated patients on VKA undergoing valve replacement surgery were studied using 2 plasma-based INR assays and 1 whole blood point-of-care INR method at multiple time points after postoperatively resuming VKA. In addition, INR levels in pooled plasma of both normal and VKA-treated individuals were compared, with 7 spiked concentrations of LMWH or unfractionated heparin (UFH) in 4 INR assays.

Results: In LMWH-bridged anticoagulated patients, the INR results obtained with HemosIL RecombiPlasTin and point-of-care Coaguchek were significantly higher than those obtained with STA Hepato Prest within 3 days after restart of VKA. After spiking LMWH or UFH in various concentrations into pooled plasma, only the STA Hepato Prest assay showed 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 showed substantial interference, with the Thromborel S assay being the most heparin-sensitive assay.

Conclusion: Differences between INR methods are seen within 72 hours after restarting VKA in postoperative patients who receive LMWH bridging. experiments using LMWH and UFH show the interference of heparin in multiple INR methods, even with concentrations below the suppliers' stated heparin interference limits.