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

Activated clotting time (ACT) is currently used to monitor high concentrations of heparin anticoagulation. A new instrument, the Hemochron® Jr Signature device, has been specifically designed to measure ACT in low-range heparin plasma concentrations (ACT-LR). The purpose of this study was to compare ACT-LR with anti-Xa activity in patients receiving low-dose i.v. heparin during vascular surgery. 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 pairs of blood samples were simultaneously collected during surgery to determine ACT-LR and anti-Xa activity. Pearson correlation, Kappa test, ROC curve and a specific clinical interpretation of the correlation were performed. ACT-LR ranged from 68 to 380 s, anti-Xa activity from 0 to 1.45 u ml−1. We observed a strong correlation between anti-Xa activity and ACT-LR (r2=0.87; P