Effects of heparin, haemodilution and aprotinin on kaolin-based activated clotting time: in vitro comparison of two different point of care devices

BACKGROUND: During cardiopulmonary bypass (CPB), measurement of kaolin-based activated clotting time (kACT) is a standard practice in monitoring heparin-induced anticoagulation. Despite the fact that the kACT test from the Sonoclot Analyzer (SkACT) has been commercially available for several years, no published data on the performance of SkACT are available. Thus, the aim of this in vitro study was to compare SkACT with an established kACT from Hemochron (HkACT). METHODS: Blood was withdrawn from 25 patients before elective cardiac surgery. SkACT and HkACT were measured in duplicate after in vitro administration of heparin (0, 1, 2 and 3 U/ml), calcium-free lactated Ringer's solution (25% and 50% haemodilution) and aprotinin (200 kIU/ml). RESULTS: A total of 600 duplicate kACT measurements were obtained from 25 cardiac surgery patients. Overall, mean bias +/- SD between SkACT and HkACT was 7 +/- 70 s (1.3% +/- 14.1%). Administration of heparin, haemodilution and aprotinin induced a comparable effect on both activated clotting time (ACT) tests. Mean bias ranged from -4 +/- 39 s (-1.7% +/- 12.9%) to 4 +/- 78 s (3.2% +/- 15.6%) for heparinzed blood samples after haemodilution or aprotinin application and increased after combined aprotinin administration and haemodilution. After haemodilution and administration of aprotinin, both ACT tests were less reliable for values >480 s in heparinized blood samples. CONCLUSION: Accuracy and performance of SkACT and HkACT were comparable after in vitro administration of heparin, aprotinin and haemodilution. Both ACT tests were considerably affected by aprotinin and haemodilution.