Toward development of a point-of-care assay of enoxaparin anticoagulant activity in whole blood

Abstract

There is need for a rapid assay to determine the efficacy of low-molecular-weight-heparin (LMWH) in whole blood. Heparinase was used to eliminate, and thereby quantify, the anticoagulant activity of the low-molecular-weight-heparin, enoxaparin. The percent change in the clotting time of whole blood in the presence of heparinase yielded the anticoagulant contribution of enoxaparin. A minimally activated assay (MAA) of whole blood clotting time was evaluated for the detection and relative quantification of enoxaparin. The assay cartridge consisted of a plain glass tube and detection magnet, with no additional sources of activation. Comparisons were also made with a point-of-care, activated partial thromboplastin time (aPTT) assay. Plasma or whole blood was spiked with enoxaparin at concentrations ranging from 0.1 to 1.0 anti-factor Xa IU/ml. A commercial preparation of heparinase I was used to digest enoxaparin, and clotting times were determined with and without heparinase incubation. Heparinase digestion caused an average shortening of clotting time of 21.1% (47.3 s) in blood spiked with 0.4 anti-Xa IU/ml enoxaparin, an amount expected in the therapeutic range; also, 0.1 anti-Xa IU/ml of enoxaparin could be reliably detected. The assay performed comparably when transferred to a point-of-care setting with heparinase being added directly to citrated blood collection tubes, followed by either MAA or aPTT assay. Strong correlations were obtained with both assays between the percent change in clotting time (after heparinase) and the added concentration of enoxaparin, or in comparison with the chromogenically measured concentration of enoxaparin. The assays for an individual blood sample can be completed within 10 min.

Anticoagulation in Chronic Hemodialysis: Progress Toward an Optimal Approach

“…A low‐range activated clotting time (ACT‐LR) was used in a Taiwanese study which did not conclude on the success of such monitoring . Addition of heparinase was used to determine anticoagulation levels with either the WBPTT or Hemochron aPTT assay; it may be used in a bedside setting as it can be completed within 10 minutes and is inexpensive . More recently, the Hemonox test was found as a valuable bedside test for monitoring anti‐Xa activity in HD patients who received tinzaparin .…”

“…The anticoagulant effect of UFH has been assessed by two bedside tests (whole‐blood partial thromboplastin time [WBPTT] and activated clotting time [ACT]) for anticoagulation monitoring during HD, but they are expensive and may lack accuracy as heparin doses are low . Regarding LMWH, several studies investigated the reliability of point‐of‐care methods for measuring their anticoagulant effect . A low‐range activated clotting time (ACT‐LR) was used in a Taiwanese study which did not conclude on the success of such monitoring .…”

How we manage blood product support and coagulation in the adult patient requiring extracorporeal membrane oxygenation

“…While the use of POC devices for determining anti-Xa activity levels has been described, they are not readily available for clinical use at this time. [47][48][49]54 Advantages of utilizing anti-Xa in monitoring ECMO anticoagulation include its mechanism of directly measuring heparin effect and the lack of influence from acute phase reactants on results. However, like the aPTT, it does not capture other elements of hemostasis such as fibrin formation.…”

“…The anti‐Xa is used by many hospitals to guide physicians in managing UFH and low–molecular‐weight heparin therapy, although recommendations for use in ECMO are not well established. While the use of POC devices for determining anti‐Xa activity levels has been described, they are not readily available for clinical use at this time 47–49,54 . Advantages of utilizing anti‐Xa in monitoring ECMO anticoagulation include its mechanism of directly measuring heparin effect and the lack of influence from acute phase reactants on results.…”