Fondaparinux anti-Xa Levels

We are using fondaparinux 2.5mg IV at the start of hemodialysis to prevent circuit clotting in 3 of out hemodialysis patients with a confirmed history of HIT. When we started this we have no access to fondaparinux anti-Xa levels so no way of monitoring. We now have access to fondaparinux anti-Xa levels and have ordered pre and post dialysis in a patient. I'm wondering if anyone else has any experience interpreting these levels for this indication in hemo patients. We are extrapolating from 2 small-scale kinetics studies.