Comparison of high-dose thrombin time with activated clotting time for monitoring of anticoagulant effects of heparin in cardiac surgical patients.

The activated clotting time (ACT) is routinely used for monitoring of heparin effects during cardiopulmonary bypass (CPB). However, ACT is not a specific assay for heparin and may be influenced by several other factors, which may be misleading with regard to the proper administration of heparin and protamine. In this pilot study, we compared a new test, the high-dose thrombin time (HiTT), with the conventional ACT test for both in vitro and in vivo heparin-induced anticoagulation. Our in vitro results showed that there were heparin dose-dependent increases in ACT and HiTT. Data on 30 adult cardiac patients indicated that HiTT correlated well with heparin concentration both after initial heparin administration and during CPB (r = 0.645 and 0.515). Hypothermia and hemodilution occurring during CPB did not alter HiTT results. ACT also correlated well with both heparin concentration and HiTT before CPB, but the linear relationship was lost during CPB. Our results suggest that HiTT is a useful assay for monitoring heparin effects during cardiac surgery, even during hypothermia and hemodilution.

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