An Evaluation of a Factor Xa-Based Clotting Time Test for Enoxaparin: A Proof-of-Concept Study.

A well-accepted test for monitoring anticoagulation by enoxaparin is not currently available. As inadequate dosing may result in thrombosis or bleeding, a clinical need exists for a suitable test. Previous in silico and in vitro studies have identified factor Xa as an appropriate activating agent, and the phospholipid Actin FS as a cofactor for a Xa clotting time (TenaCT) test. A proof-of-concept study was designed to (1) explore the reproducibility of the TenaCT test and (2) explore factors that could affect the performance of the test. In vitro clotting time tests were carried out using plasma from 20 healthy volunteers. The effect of enoxaparin was determined at concentrations of 0.25, 0.50, and 1.0 IU/mL. Clotting times for the volunteers were significantly prolonged with increasing enoxaparin concentrations. Clotting times were significantly shortened for frozen plasma samples. No significant differences in prolongation of clotting times were observed between male and female volunteers or between the 2 evaluated age groups. The clotting times were consistent between 2 separate occasions. The TenaCT test was able to distinguish between the subtherapeutic and therapeutic concentrations of enoxaparin. Plasma should not be frozen prior to performing the test, without defining a frozen plasma reference range. This study provided proof-of-concept for a Xa-based test that can detect enoxaparin dose effects, but additional studies are needed to further develop the test.