Stability of Direct Oral Anticoagulants Concentrations in Blood Samples for Accessibility Expansion of Chromogenic Assays

Background and Objectives: Direct oral anticoagulants (DOACs) are used for minimising the risk of thromboembolic events. In clinical practice, there is no need to measure DOAC concentration in the routine. Nevertheless, there are cases where such measurements are necessary, as the European Society of Cardiology’s guideline recommends. However, determining DOAC levels is not available for everyone due to chromogenic assay availability limitations from sample storage problems, as tests are performed only in a few healthcare settings. This study aimed to assess whether more applicable storage conditions could be used for transportation to provide chromogenic assays for outpatient healthcare and other hospitals’ practices. Materials and Methods: Chromogenic assays measuring anti-FXa (for rivaroxaban and edoxaban) and anti-FIIa (for dabigatran) were used. Concentrations were determined immediately after blood collection as baseline value: (1) after the storage of citrated whole blood in refrigerator (+2–8 °C); (2) of citrated plasma in refrigerator (+2–8 °C); and (3) of citrated frozen plasma (−20 °C) on the third and seventh days of storage. Acceptable change limits were considered stable if the deviation did not exceed ±20% of the baseline value. Results: The median (Cl 95%) baseline value of rivaroxaban was 168 (147–236) ng/mL; of dabigatran 139 (99–178) ng/mL; and of edoxaban—174 (135–259) ng/mL. The median deviation from a baseline value stored as citrate whole blood samples (+2–8 °C) was 5.4% and 3.4%; as citrated plasma (+2–8 °C) was 0.4% and −0.6%; and as citrated frozen plasma (−20 °C) was −0.2% and 0.2% on the third and seventh days of storage, respectively. Conclusions: Our data suggest that whole blood samples stored in a refrigerator, as well as citrated plasma samples stored in both the refrigerator and freezer, preserve DOAC concentration stable at +2–8 °C or −20 °C for up to 7 days, and are suitable for transportation, except for low-concentration samples.