A quick anti-Xa-activity-based whole blood coagulation assay for monitoring unfractionated heparin during cardiopulmonary bypass: A pilot investigation

We developed a quick and easy method to perform anti-Xa-activity-based whol e blood assay and assessed its reliability for online monitoring of unfract ionated heparins (UFHs) during cardiopulmonary bypass. Seventy-five microli ters of a mixture of 1:3 large- and small-range Heptest(R)(TM) 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 ov erlaid with 75 mu L of Recalmix for recalcification. One-hundred fifty micr oliters of citrated whole blood were added and measurements performed. In v itro, the linearity of the test over a range of 1-8 IU/mL UFH, as well as t he influence of variations in hematocrit (60%, 30%, and 20%), plasma coagul ation factors (50%, 30%, and 20%) and platelets (100, 50, and 20 x 10(3)/mu L) on the test results were assessed. In vivo measurements performed durin g cardiopulmonary by pass were compared with the chromogenic assay. The tes t revealed linearity to concentrations of 6 IU/mL of UFH and was not signif icantly influenced by the variations in the in vitro set-up despite a prolo ngation in samples with a hematocrit of 60%. In vivo, the correlation to th e 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 cou ld 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 pract ice.