The aim of the study was to evaluate the anti-Xa-activity (aXa) of selective and non-selective factor Xa inhibitors in patients with systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS) patients according to clinical implications and laboratory parameters. Materials and methods. Clinical and laboratory data were analyzed retrospectively in SLE and APS patients who protractedly received low weight molecular heparins (LWMH) and selective factor Xa inhibitors fondaparinux and rivaroxaban. The study included 70 patients in the middle age 39 [31; 43] years: 15/70 (21%) - with SLE, 10/70 (14%) - with APS and 45/70 (65%) - with SLE and APS (SLE+APS). All the patients received anticoagulants: 29 patients nadroparin (98.3 [67.8; 129.5] IU/kg/day), 29 patients fondaparinux (5 [5; 7.5] mg/day), 3 patients - enoxaparin (1.2 [0.8; 1.5] mg/day) and 9 patients - rivaroxaban (20 mg/day). All the patients signed informed consents. Results. aXa therapeutic range of 0.1-1.5 IU/ml was found in 43/70 (61%) patients, low aXa - in 14/70 (20%) and high aXa - in 13/70 (19%) patients. Patients with low aXa underwent anticoagulant dose correction. There were not any major bleedings and thrombosis relapses in the study. Increased aXa was more common in patients, who took fondaparinux (31%), than in those, who took nadroparin (7%) and rivaroxaban (23%), p=0.02. Patients with enoxaparin had normal aXa range. In the absence of bleeding in SLE and APS patients, received anticoagulants in standardized therapeutic dose, the next factors influenced the aXa range excess: valvular heart disease (VI ID) with the 3rd stage of mitral valve insufficiency as a result of aseptic Libman-Sacks endocarditis (odds ratio - OR 9.02, 95% confidential interval CI [1.53; 53.12], p=0.015), peripheral artery disease in analogy with arteritis obliterans (AO) (OR 6.86, 95% CI [1.25; 37.71], p=0.027), and also triple-positivity of all types of antiphospholipid antibodies (OR 4.93, 95% CI [1.11; 21.99], p=0.036). According to found logistic regression model, aXa range excess risk can be prognosticated by the next formula: Z = -3.98 + 2.2 x VHD (yes-1/no-0) + 1.9 x AO (yes-1/no-0) + 1.6 x Triple-positivity (yes-1/no-0). Classified function value 7.39 defines the patients group with aXa range excess. Thus the value Z>0.39 indicates aXa range excess in the absence of bleeding, herewith sensibility is of 77% and specificity is 86%, positive prognostic value is 84.3%. Conclusion. In SLF and APS patients the next clinical and immunologic manifestations influenced the aXa therapeutic range excess: peripheral artery disease in analogy with AO, earlier aseptic Libman-Sacks endocarditis with the 3rd stage of mitral valve insufficiency and triple-positivity of all types of antiphospholipid antibodies, that does not need LWMH and fondaparinux dose correction. In contrast, anticoagulant dose reduction can cause clinical symptoms progression. Therapeutic aXa range in such patients should be extended.
