Anticoagulation monitoring during vascular surgery: accuracy of the Hemochron low range activated clotting time (ACT-LR)

Background. Activated clotting time (ACT) is currently usedto monitor high concentrations of heparin anticoagulation. Anew instrument, the Hemochron® Jr Signature device, hasbeen specifically designed to measure ACT in low-range heparinplasma concentrations (ACT-LR). The purpose of this study wasto compare ACT-LR with anti-Xa activity in patients receivinglow-dose i.v. heparin during vascular surgery. Methods. Thirty patients, undergoing arterial vascular surgery,were included in the study and received unfractionated heparin(initial dose 50 u kg^–1). One hundred and thirty-two pairsof blood samples were simultaneously collected during surgeryto determine ACT-LR and anti-Xa activity. Pearson correlation,Kappa test, ROC curve and a specific clinical interpretationof the correlation were performed. Results. ACT-LR ranged from 68 to 380 s, anti-Xa activity from0 to 1.45 u ml^–1. We observed a strong correlation betweenanti-Xa activity and ACT-LR (r²=0.87; P<0.0001). Accuracyof ACT-LR was good for anti-Xa activity up to 0.6 u ml^–1(Kappa, 0.94; accuracy, 97%) and 0.8 u ml^–1 (Kappa, 0.79;accuracy, 90%), and poor for anti-Xa activity above 1 u ml^–1(Kappa, 0.59). A clinical interpretation of the correlationgraph found 98% of measured ACT-LR values to be accurate. Conclusion. Hemochron® Jr Signature provides measurementsof ACT-LR, which are accurate for monitoring heparin anticoagulationat anti-Xa activity below 0.8 u ml^–1.