Laboratory Monitoring Needs to Be Improved
One of the problems in dealing with direct oral coagulants (DOACs) is the fact that specific laboratory parameters for detecting these drugs are not commonly used. However, many labs feature a test that reacts highly sensitively to factor Xa inhibitors—namely, measuring the antithrombin concentration. For this parameter, the testing systems that are mostly used nowadays actually do measure the anti-Factor Xa effect, which antithrombin does have, too (1). Using this method will give antithrombin values that are too high, under the influence of factor Xa inhibitors. In this case, the combination of lowered Quick value and seemingly raised antithrombin is a reliable indicator of a factor Xa inhibitor.
It is also possible to calibrate a reagent used for measuring antithrombin with a factor Xa inhibitor. A major obstacle in this setting is the compulsory, laborious in-house validation if a reagent is used outside its licensed application scope.
Usually the measurement of the anti-factor Xa activity is required to be calibrated to the medication actually used. In routine laboratory diagnostics, however, it is a well-known fact that the results are largely interchangeable. A high concentration of rivaroxaban corresponds to a high concentration of edoxaban or apixaban and also a high concentration of low molecular weight heparin.
Laboratories would have to go to great lengths in order to provide in parallel the measurement of anti-factor Xa activity for rivaroxaban, apixaban, edoxaban, and low molecular weight heparin. It would therefore be pragmatic and a significant progress in treating such emergencies to agree on a generally calibrated anti-factor Xa activity. Moreover, there is a vast potential for error if, for example, a patient is taking rivaroxaban but erroneously, anti-factor Xa activity for edoxaban is ordered and appears on the laboratory report.
Dr. med. Norbert Ostendorf
St. Katharinen-Hospital Frechen
Conflict of interest statement
The author declares that no conflict of interest exists.
|1.||Demers C, Henderson P, Blajchman MA, et al.: An antithrombin III assay based on factor Xa inhibition provides a more reliable test to identify congenital antithrombin III deficiency than an assay based on thrombin inhibition. Thromb Haemost 1993; 69: 231–5 MEDLINE|
|2.||Maegele M, Grottke O, Schöchl H, Sakowitz O, Spannagl M, Koscielny J: Direct oral anticoagulants in emergency trauma admissions—perioperative management, and handling hemorrhage. Dtsch Arztebl Int 2016; 113: 575–82 VOLLTEXT|