A Quick Anti-Xa-Activity-Based Whole Blood Coagulation Assay for Monitoring Unfractionated Heparin During Cardiopulmonary Bypass: A Pilot Investigation

Abstract

We developed a quick and easy method to perform anti-Xa-activity-based whole blood assay and assessed its reliability for online monitoring of unfractionated heparins (UFHs) during cardiopulmonary bypass. Seventy-five microliters of a mixture of 1:3 large- and small-range Heptest®™ reagent were transferred into blank cartridges of the ACT II device. The plastic flags for clot detection and stirring the sample and reagent were inserted and overlaid with 75 μL of Recalmix for recalcification. One-hundred fifty microliters of citrated whole blood were added and measurements performed. In vitro, the linearity of the test over a range of 1–8 IU/mL UFH, as well as the influence of variations in hematocrit (60%, 30%, and 20%), plasma coagulation factors (50%, 30%, and 20%) and platelets (100, 50, and 20 × 103/μL) on the test results were assessed. In vivo measurements performed during cardiopulmonary bypass were compared with the chromogenic assay. The test revealed linearity to concentrations of 6 IU/mL of UFH and was not significantly influenced by the variations in the in vitro set-up despite a prolongation in samples with a hematocrit of 60%. In vivo, the correlation to the chromogenic test was R = 0.90. The ACT II anti-Xa-UFH assay performed in whole blood was reliable when used over a wide range of conditions that could be encountered clinically. Although the test is useful for point-of-care monitoring, the necessity of individual calibrations and pipetting in the operation room requires further automation before its use in clinical practice. Implications The ACT II anti-Xa-unfractionated heparin assay allows for reliable monitoring of large concentrations of UFH over a wide range of hematocrit, platelet, and coagulation factor levels. Further evaluation of this point-of-care device is indicated.