An Evaluation of Factors Affecting Activated Coagulation Time

Objective: Although failure to achieve an adequate activated coagulation time (ACT) after full heparinization before cardiopulmonary bypass often is attributed to antithrombin (AT) deficiency, it remains unclear if this is a causative mechanism of decreased heparin responsiveness. Therefore, the authors determined the relationship between AT and other coagulation-related factors that affect the ACT measurement and heparin sensitivity index before the establishment of cardiopulmonary bypass. Design: Observational study. Setting: University medical center. Participants: Adult elective cardiac surgical patients. Interventions: Preoperative data collection included demographics, type of preoperative medical therapy, hemoglobin, platelet count, and AT. Intraoperative measurements included ACT and anti-Xa activity. Results: Of the 203 patients enrolled in this study, 10% (n = 21) did not achieve an adequate ACT (>= 400 seconds) after full heparinization. Subnormal AT activity (55%-79%) was not related to a low ACT and a low heparin sensitivity index. Preoperative low-molecular-weight heparin therapy did not cause a decreased ACT response. However, preoperative low hemoglobin levels and high platelet counts were associated with a decreased ACT. Conclusions: All these observations suggest that failure to achieve an adequate ACT is, in general, not an indicator of AT deficiency but could be affected by high platelet counts and low hemoglobin levels.