Christoph K. Hofer

Background: Sonoclot is used to measure kaolin-based activated clotting time (kACT) for heparin management. Apart from measuring kACT, the device assesses the patient’s coagulation status by glass bead–activated tests (gbACTs; measuring also clot rate [CR] and platelet function [PF]). Recently, a new version of the Sonoclot has been released, and the redesign may result in performance changes. The aim of this study was to evaluate and compare the performance of the new (S2) and the previous (S1) Sonoclot. Methods: The S1 was used in the routine management of 30 patients undergoing elective cardiac surgery. Blood samples were taken at baseline (T1), after heparin administration (200 U/kg, 100 U/kg; T2 and T3), during cardiopulmonary bypass (T4), after protamine infusion (T5), and before intensive care unit transfer (T6). Kaolin-based activated clotting time and gbACTs were measured in duplicate by both the old and the new device and performance compared by Bland-Altman analysis and percentage error calculation. Results: A total of 300 kACT and 180 gbACTs were available. Bland-Altman analysis for kACT revealed that S2 consistently reported results in shorter time compared to S1 (overall = −14.7%). Comparing S2 and S1, the glass bead–activated tests showed mean percentage differences of −18.9% (gbACTs), +37.4% (CR), and −3.7% (PF). Conclusion: Since clotting is faster in the new S2 compared to S1, shorter clotting times have to be considered in clinical practice. The use of S2 kACT in heparin management will result in higher heparin and protamine dosing unless heparin kACT target values are adjusted to correct for the differences in results between S1 and S2.