PB0128 - Comparison between anti-factor Xa and heparin assays to measure plasma levels of three different types of direct oral anticoagulants in patients with non-valvular atrial fibrillation

Background: Direct oral anticoagulants (DOAC) inhibit the active site of thrombin or factor (F) Xa. Although drug monitoring is not routinely requested, the measurement of DOAC levels in plasma is useful in some cases.

Aims: In this study, we investigated the trough and peak levels of three different DOAC in patients with non-valvular atrial fibrillation (NVAF) and compared results between anti-Xa and heparin assays.

Methods: A total of 566 NVAF patients were included for the study. Among them, 321 patients were treated with 5 mg apixaban orally twice daily, 208 with 60 mg edoxaban daily, and 37 with 20 mg rivaroxaban daily. Blood samples were collected using 3.2% sodium citrate tubes after three weeks of DOAC treatment and both trough and peak levels were measured using Biophen DiXal (anti-Xa) and Heparin LRT chromogenic assays (Hyphen BioMed, Neuville Sur Oise, France) with a Sysmex CS-5100 analyzer (Sysmex Corp., Kobe, Japan). Prothrombin time (PT) and activated partial thromboplastin time (aPTT) tests were also performed.

Results: The median age was 69, 69.5, and 72 years in apixaban, edoxaban and rivaroxaban treatment, respectively. The trough and peak levels for apixaban, edoxaban, and rivaroxaban were 109.58±68.22, 203.0±108.76, 52.85±38.51, 225.89±116.07, 75.57±79.38, and 292.24±135.81 ng/mL, respectively with anti-Xa assay. Heparin LRT assays for the trough and peak levels with apixaban, edoxaban and rivaroxaban were 116.78±68.88, 215.3±109.63, 50.94±27.37, 217.67±109.16, 65.77±76.51, and 283.22±144.42 ng/mL, respectively. The peak levels were statistically higher with all three DOAC than those of trough (P < 0.0001). Both the anti-Xa and heparin assays showed excellent correlations (r≥0.97, P< 0.0001) regardless of the trough or peak levels and DOAC types.

Conclusion(s): The results suggested that chromogenic method for the assay of direct factor Xa inhibitors showed reliable trough and peak levels for three types of DOAC in NVAF patients. We could obtain comparable results between the anti-Xa and heparin assays.