PB1149 - International Normalised Ratio measurement during bridging with Low Molecular Weight Heparin

Background: Monitoring of anti-coagulation therapy is challenging during heart valve replacement surgery. Patients on vitamin K antagonist (VKA) therapy are temporarily switched to the Low Molecular Weight Heparin dalteparin. The day after surgery the VKA is resumed. Simultaneous dalteparin gifts can be terminated after two International Normalised Ratio (INR) results in the therapeutic range on two consecutive days.

Aims: Reliable INR measurements in this specific patient group.

Methods: Three INR methods are compared in 22 samples obtained from patients undergoing valve replacement: ACL-TOP 350 (Werfen, Recombiplastin), STA-R Max (Stago, Hepatoprest) and Coaguchek Pro-II (Roche).

Results: - INR results obtained with ACL-TOP are significantly higher than STA-R Max results on day 2 and 3 after resuming VKA therapy. From day 4 onward STA-R Max results are often somewhat higher than ACL-TOP results.
- Coaguchek results were not significantly different from ACL-TOP and STA-R Max results.
- No differences were observed between prophylactic and therapeutic dalteparin therapy.

Variation in results can be explained by differences in sensitivity of reagents for (vitamin K dependent) coagulation factors and variable concentration of active coagulation factors when VKA therapy is resumed. The water balance and fibrinogen concentration are changing during these days after surgery. Also the sensitivity for dalteparin may differ, even though the reagents contain an heparin neutralizing agent.

Conclusion(s): In the first three days after resuming VKA therapy, INR is significantly higher in ACL-TOP measurements compared to STA-R Max results. From day 4 onward, INR results are more equal between the methods. Although earlier measurement would be logistically interesting, we recommend measuring on day 4 and later, which is in agreement with the national guidelines (https://lta-antistollingszorg.nl).