title: Activated clotting time systems vary in precision and bias and are not interchangeable when following heparin management protocols during cardiopulmonary bypass.
abstract: OBJECTIVE
  Our aim was to test the hypothesis that new activated clotting time (ACT) technology, with modifications to instruments and reagents designed to detect earlier clot formation, would be associated with more precise but lower results. A secondary objective was to evaluate the potential impact of any change in ACT measurement on heparin requirements during cardiopulmonary bypass (CPB).
  
  
  METHODS
  We compared the precision of two newer ACT systems: Actalyke, Helena Laboratories, Beaumont, TX and Hemochron Response, International Technidyne Corporation, Edison, NJ and assessed their bias with reference to a standard ACT system (Hemochron 801, International Technidyne Corporation, Edison, NJ). Bland-Altman analysis was applied to 81 duplicate samples from 22 patients undergoing CPB or percutaneous coronary interventions (PCI), covering the full clinical range of ACT values. We also estimated the change in heparin dose required to use the Actalyke rather than the Hemochron 801 results, to achieve our target ACT for CPB (480 seconds), and used a mixed model to test for significance.
  
  
  RESULTS
  The precision of the Actalyke was superior to the Hemochron Response (mean difference of duplicates +/- 0.1% versus +/- 4.2%). There was no significant bias (p = 0.93) between the results from the standard analyzers (Hemochron 801 and Response), but the results from the modified system (Actalyke) were on average 18% lower than the Hemochron 801 (p < 0.0001). Estimated heparin requirements established that fifty percent of CPB patients would have required additional heparin (5000 to 17500 units), an average increase of 1060 units per patient (p = 0.05), if the Actalyke values were used to guide anticoagulation during CPB.
  
  
  CONCLUSIONS
  Our results support the hypothesis that the modified technology (Actalyke) is associated with more precise but lower ACT results. We estimated these lower values would lead to increased heparin dosing during CPB. The impact of this increase on bleeding after cardiac surgery with CPB is controversial and requires further study.
authors.affiliation: Department of Anesthesiology, Duke University Medical Center, Durham, NC 27710, USA. welsb001@mc.duke.edu
authors.forename: Ian J
authors.initials: IJ
authors.lastname: Welsby
authors.forename: Elizabeth
authors.initials: E
authors.lastname: McDonnell
authors.forename: Habib
authors.initials: H
authors.lastname: El-Moalem
authors.forename: Mark
authors.initials: M
authors.lastname: Stafford-Smith
authors.forename: John G
authors.initials: JG
authors.lastname: Toffaletti
mesh_terms: D000328:Adult; D000925:Anticoagulants / Q000008:administration & dosage*; D001780:Blood Coagulation Tests / Q000295:instrumentation*; D002315:Cardiopulmonary Bypass; D006493:Heparin / Q000008:administration & dosage*; D006801:Humans; D008991:Monitoring, Physiologic; D015203:Reproducibility of Results; D014914:Whole Blood Coagulation Time
chemical_list: D000925:Anticoagulants; D006493:Heparin