PB1469 - Anti-Xa monitoring in patients with acute non-cirrhotic porto-mesenteric venous thrombosis treated with low molecular weight heparin

Background: Therapeutic anticoagulation with low molecular weight heparin (LMWH) is used for treating porto-mesenteric venous thrombosis. Although monitoring using the anti-Xa assay to evaluate LMWH treatment, the role of this assay has not been established in patients with non-cirrhotic porto-mesenteric venous thrombosis.

Aims: To assess peak anti-Xa levels ([anti-Xa]) in adults with acute non-cirrhotic porto-mesenteric venous thrombosis (ANCPMVT) treated with LMWH and whether this impacts on recanalisation or bleeding rates.

Methods: Single-centre retrospective (2021-2023) review of adults with ANCPMVT. Patients received therapeutic LMWH (tinzaparin or enoxaparin) either once or twice daily (Table 1). [Anti-Xa] were measured 3 to 6 hours after ≥3 doses of LMWH. Patients with cirrhosis, on alternate anticoagulation, with creatinine clearance < 30mL/min, or with thrombocytopenia < 50x109/L were excluded. Outcomes evaluated were first peak [anti-Xa], recanalisation rates (3 months) and bleeding (major or clinically significant non-major) during hospitalisation

Results: 18 patients presented with 19 episodes of ANCPMVT (Table 2). Most episodes (n=18) were treated initially with systemic low-dose and/or catheter-directed thrombolysis. The majority (94.7%) were treated with twice-daily LMWH. Therapeutic [anti-Xa] (range: 0.5-1.0 IU/mL) were achieved in only 21% (n=4) of episodes. There was no correlation between Antithrombin activity and [anti-Xa] (r=0.0681). There was no difference between tinzaparin and enoxaparin in achieving therapeutic peak [anti-Xa] (P=0.35). Recanalisation rates (full/partial) at 3 months were low (31.6%) and did not differ between those with therapeutic and subtherapeutic [anti-Xa] (P=0.23), or between LMWH regimens (p=0.13). Bleeding rates (21.1%) did not differ between those with therapeutic and subtherapeutic [anti-Xa] (any bleeding versus no bleeding, P=0.31).

Conclusion(s): Standard-dose LMWH for treatment of ANCPMVT was not associated with therapeutic peak [anti-Xa] in most patients in this study. Achieving therapeutic [anti-Xa] was not different between different LMWH regimens. The anti-Xa level did not appear to influence recanalization and bleeding rates, but this requires larger studies to confirm.