SAT0441 Predictive value of antiphospholipid antibodies in the acute phase of deep vein thrombosis

Background Deep vein thrombosis (DVT) is frequent and potentially life threatening disease with tendency to reoccur. Anticoagulant treatment of the first episode of DVT usually lasts 3 months. Antiphospholipid syndrome (APS) is an important cause of DVT. However, the APS can be confirmed only 24 weeks after DVT according to the current APS classification criteria.1 Thus, undiagnosed APS patients, who cease anticoagulant therapy after 3 months, might be exposed to a greater risk for recurrent venous thromboembolism. Studies evaluating the significance of positive antiphospholipid antibody (aPL) test in the acute phase of DVT are lacking. Objectives To evaluate whether positive aPL test at the time of acute DVT diagnosis is predictive of APS. Methods Patients with acute DVT were included into a 24 month prospective study. All patients were given anticoagulants. aCL IgG/IgM and anti-β2GPI IgG/IgM/IgA antibodies were determined by our in-house ELISA2 at inclusion and then every 4 weeks for the first 24 weeks. The last aPL measurement was performed 24 months after inclusion into the study. APS was confirmed if a patient tested positive (medium or high positive aCL and/or presence of anti-β2GPI) 12 and 24 weeks after DVT. Lupus anticoagulants (LA) were tested after cessation of anticoagulation. Results 196 patients (111 male, 85 female, age 54±2 years) included in the study had aPL titer assessed at least 5 times. Ultimately, 20/196 (10.2%) patients fulfilled APS classification criteria. Among these, 15/20 (75%) patients had medium or high titer aPL at the time of acute DVT (1 of them had double positive aPL and 2 of them had multiple positive aPL at first aPL determination). Two patients (10%) had low positive aCL IgG and one had low titer aCL IgM. Two patients (10%) were negative for aPL, but had later fulfilled APS criteria due to positive LA. APS was not established in 176/196 (89.8%) patients. Among these, 146/176 (83%) patients were negative for aPL at inclusion, while 30/176 (17%) had low titer aCL IgM or aCL IgG. Altogether, diagnostically important aCL IgG/IgM and/or anti- β2GPI titer at the time of acute DVT had 83% specificity and 90.5% sensitivity for APS. Isolated low titer aCL IgG were more frequent in patients with APS than in patients without APS (χ2=125.6; p Conclusions Here we show that in acute phase of DVT, positive medium or high titer aCL IgG/IgM or anti-β2GPI is suggestive of APS. In these patients continuation of anticoagulation beyond the initial 3 months should be considered. Patients with negative aPL in the acute phase of DVT do not need further aPL testing; however, LA should be determined. Low aPL titre at the time of acute DVT deems further testing imperative. References [1] Miyakis S, et al.Thromb Haemost2006;4:295–306.2. [2] Cucnik S, et al. Clin Chem Lab Med2000;38:777–783. Disclosure of Interest None declared