Evaluation of the TAS Analyzer and the Low-Range Heparin Management Test in Patients Undergoing Extracorporeal Membrane Oxygenation

Abstract

Background: The new Low-Range Heparin Management Test (LHMT), a method for point-of-care testing (POCT) of heparinization, has been designed to function at the low to moderate heparin concentrations typically found in patients undergoing extracorporeal membrane oxygenation (ECMO). In this study, the new method is compared with two POCT methods and a laboratory-based anti-Xa assay. Methods: We obtained 760 whole blood samples from 13 patients undergoing ECMO. All samples were tested immediately by the LHMT, the Activated Clotting Time (ACT) test, and its low-range counterpart (ACT-LR). Aliquots from the same blood draw were frozen for later anti-Xa analysis using the Diagnostica Stago method on the Roche Cobas Fara-II. Results: The precision was best for duplicate citrated LHMT samples (CV = 3.1%). LHMT clotting times (overall median, 162 s) were typically shorter than ACT or ACT-LR times (247 and 235 s, respectively). The relationship between the LHMT and the other POCT methods differed significantly from patient to patient (P <0.0001), and a meaningful single relationship between the methods could not be obtained. The overall correlation coefficient between clotting time values and actual heparin concentrations was ≤0.48 for each of the instruments tested, although time plots of each analyzer’s data suggested that they detected heparin dosage changes within single patients. Conclusions: The performance of the LHMT on the TAS Analyzer is equivalent to that of currently commercially available POCT methods. The lack of agreement between absolute clotting time values and heparin concentrations suggests the need for reexamination of current ECMO patient management strategy.

Anticoagulation monitoring during vascular surgery: accuracy of the Hemochron ® low range activated clotting time (ACT-LR)

“…11 On the other hand, no correlation had been reported for low concentrations of anticoagulation between Hemochron Ò Jr ACT-LR values and anti-Xa activity during ECMO. 19 Our different results could be explained by physiological factors during ECMO, such as intense coagulopathy, hypothermia and haemodilution. This study confirms that low anti-Xa activity is the most appropriate setting for Hemochron Ò Jr II Signature device with low-range cartridges.…”

“…ACT-LR has already been compared with laboratory-based anti-Xa activity in patients undergoing extracorporeal membrane oxygenation (ECMO). 19 Several factors involved in the relationship between ACT and laboratory assay could explain the poor correlation found.…”

Trends and Emerging Technologies in Extracorporeal Life Support: Results of the 2006 ECLS Survey

“…Although ACTs remain the standard of care for anticoagulation monitoring during ECLS (98%), new data suggest other methods may be more valuable for measuring systemic anticoagulation over long periods of time (25), such as thrombin generation and heparin levels via anti-Xa activity. Studies have shown that ACTs do not correlate with thrombin generation in the pediatric population, possibly because of increased hemodilution and lower fibrinogen levels compared with the adult population.…”

Anticoagulation Monitoring Part 2: Unfractionated Heparin and Low-Molecular-Weight Heparin

“…The target ACT varies with technique and patient characteristics. 62,63 For renal replacement therapy, the goal of anticoagulant therapy is to limit filter and circuit clotting. To accomplish this, an ACT of 170–220 seconds has been recommended.…”