Ability of Activated Clotting Time Measurements to Monitor Unfractionated Heparin Activity During NonCardiac Arterial Procedures

Background: Activated clotting time (ACT) measurements are frequently used to monitor unfractionated heparin activity during noncardiac arterial procedures (NCAP). Accuracy of ACT-guided heparinization is mandatory to prevent heparin under and overdosing, thereby minimizing thrombo-embolic complications (TECs) and bleeding risk. The main objective of this study was to investigate accuracy of ACT to monitor heparin activity during NCAP using the Hemostasis Management System Plus (HMS) with high-range (HR) cartridges. ACT values were compared with anti-Xa measurements, regarded as the standard test to measure active heparin. Methods: This was a single-center, prospective, observational cohort study. Perioperative blood samples of patients undergoing NCAP between December 2022 and September 2023 were used to perform bedside ACT measurements and anti-Xa assays in the clinical laboratory. Primary outcome was the association between ACT and anti-Xa measurements. TEC, mortality, and bleeding complications within 30 days postoperatively or during primary admission were also scored. Results: 196 pairs of ACT and anti-Xa measurements were performed in 34 patients. Strong correlation was observed between anti-Xa and ACT measurements (Pearson's correlation coefficient = 0.84, 95% CI = 0.79–0.87, P < 0.001). Apart from anti-Xa, no additional variables were associated with ACT in multivariate linear regression analyses (regression coefficient β = 36.7, 95% CI = 33.3–40.1, P < 0.001). Bleeding complications occurred in 29% of the patients, while both TEC and mortality were observed in one patient. Conclusions: Strong correlation and an independent association were observed between heparin activity measured by anti-Xa and ACT using the HMS Plus.