Heparinase in the Activated Clotting Time Assay

The activated clotting time (ACT) is routinely used to monitor heparin during cardiopulmonary bypass surgery. Activated clotting times may be influenced by a number of factors other than heparin. The presence of heparin in blood samples disguises the occurrence of non-heparin-related changes in coagulation function. During cardiopulmonary bypass, it is difficult to ascertain baseline clotting time fluctuations with ACT alone. Previous attempts to establish accurate baseline data were imprecise and involved extensive sample handling. In this study, we present data obtained using a modified (ACT) assay that incorporates heparinase. The heparinase test cartridge (HTC) instantaneously, specifically, and completely removes heparin in the blood sample at the initiation of the test. In conjunction with standard ACT techniques, the clinician is provided with heparin-independent (baseline) and functional clotting data. The HTC/ACT assay was used in a case study involving 19 patients undergoing cardiopulmonary bypass surgery. The data gathered indicate the usefulness of this assay in monitoring incidents of baseline drift, hemodilution, and hypercoagulation and the efficacy of protamine reversal.