β-Antithrombin Levels in Patients with Venous Thromboembolism

Beta-antithrombin (β-AT), the isoform of antithrombin (AT) with a higher affinity for heparin, constitutes 5–10% of total AT in plasma. There are limited data regarding β-AT activity levels in thrombotic disorders. In our study, we analyzed samples from 200 non-AT-deficient patients who had experienced venous thromboembolism (VTE) compared to 200 healthy controls. Total AT activity was measured using a chromogenic anti-factor Xa assay. To measure β-AT, we used elevated NaCl (1.1 M) in the reagent to inhibit the heparin binding of α-AT. There were no significant differences in total AT activity (median (IQR)) levels between the control and VTE groups (100 (93–109)% and 99 (94–109)%, respectively; p = 0.955). However, the β-AT activity levels (median (IQR)) and the ratio of β-AT to total AT (mean ± SD) were significantly higher in the VTE group compared to the control group (93.3 (90.3–97.3)% vs. 89.3 (84.0–95.0)% and 9.34 ± 0.68% vs. 8.86 ± 0.88%; p < 0.001). β-AT activity levels and the ratios in the upper third were strongly associated with a higher risk of VTE (OR (95% CI): 5.78 (3.08–10.87) and 6.15 (3.36–11.24), respectively). Our study demonstrated an elevation of plasma levels of β-AT in patients with VTE. Further research is necessary to clarify the pathophysiological significance of this finding.