Resolving DOAC interference on antithrombin activity testing on a FXa based method by the use of activated carbon

Direct oral anticoagulants (DOACs) may cause falsely increased levels of antithrombin (AT) activity depending on the AT activity method and the specific target of the DOAC. Activated carbon (AC) has proven to remove DOAC interference on PT, aPTT and LA assays. We evaluate whether AC could be useful to resolve DOAC interference on AT assays. Normal pooled plasma (NPP) was diluted to obtain AT activity of 25 %, 50 % and 75 % respectively. The diluted NPPs were spiked with DOACs (apixaban, edoxaban, dabigatran and rivaroxaban) in concentrations of respectively 100, 250 and 500 ng/ml. DOAC concentrations and AT activity were tested at baseline and after treatment with 20 mg/ml AC. AT activity was measured with a FXa-based method (HemosIL Liquid Antithrombin®, Werfen). All DOAC concentrations were below the limit of quantification (LoQ) after addition of AC. DOAC interference on AT activity testing was removed by adding AC, resulting in correctly diagnosing low levels of AT for all dilutions. The influence of DOACs on AT activity was directly correlated to the concentration of the DOAC. As expected, only the anti-FXa DOACs influenced the used assay. AC effectively removes anti-FXa DOAC interference on FXa-based AT assays.