Comparison of Hemochron and HemoTec activated coagulation time target values during percutaneous transluminal coronary angioplasty

St. Luke's Episcopal Hospital, Texas Heart Institute, Baylor College of Medicine, Houston 77225.

OBJECTIVES. The aim of this study was to determine whether activated coagulation time measurements from Hemochron and HemoTec machines can be used interchangeably and whether similar activated coagulation time target ranges for adequate anticoagulation can be applied to both machines. BACKGROUND. Adequate anticoagulation is necessary for the safe performance of intravascular interventions such as percutaneous transluminal coronary angioplasty. In current practice, anticoagulation status is frequently assessed by way of the activated coagulation time with one of two commercially available systems, HemoTec and Hemochron. Each one employs a different technique to determine the time of clot formation; however, the same target activated coagulation time values for adequate anticoagulation have been used interchangeably in published studies. METHODS. A total of 311 paired samples were compared in 113 high risk patients undergoing angioplasty enrolled in a randomized trial of a platelet glycoprotein IIb/IIIa receptor antibody. Simultaneous activated coagulation time measurements were obtained before and after administration of heparin, and the difference between the values of both machines was calculated. The relation between the Hemochron and HemoTec values was determined by using linear regression analysis. All activated coagulation time measurements were classified as either therapeutic or subtherapeutic using an arbitrary activated coagulation time target of 300 s. RESULTS. There was a correlation between values from the two machines (r = 0.86), but the Hemochron values were consistently higher than the HemoTec values by a mean value +/- SD of 28 +/- 29%, with wide individual variation. After heparin administration, there was a significant (p < 0.0001) difference between the number of measurements classified as therapeutic by HemoTec (53%) and by Hemochron (94%). CONCLUSIONS. HemoTec and Hemochron activated coagulation time measurements cannot be used interchangeably. Appropriate target activated coagulation time ranges to determine adequate anticoagulation during coronary angioplasty need to be established for both machines; the target range for one machine should not be extrapolated to the other.

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