The antiphospolipid syndrome (APS) is a systemic autoimmune syndrome, characterized by thrombotic events and/or by recurrent miscarriages, and by the persistent presence of circulating antiphospholipid antibodies (aPL). The diagnostic criteria are defined by strict guidelines and require clin. characteristics (vascular thrombosis or pregnancy complications) and the persistent presence of aPL: lupus anticoagulant (LA), and/or anticardiolipin antibodies (aCL >99th percentile), and/or anti-β2-glycoprotein I antibodies (a-β2GpI >99th percentile) (1-4). LA are antibodies directed against neg. charged phospholipids/protein complexes, resulting in prolonged clotting times in phospholipid dependent tests (e.g. APTT). Diagnosis of antiphospholipid syndrome (APS) relies predominantly on laboratory results. Therefore, adequate laboratory detection of antiphospholid antibodies, such as LA is clin. relevant. Assays must be sufficiently sensitive and highly specific to classify APS-pos. patients correctly, as they have impact on clin. decisions for oral anticoagulant treatment (3, 5-7). Patients with thrombosis and aPL antibodies may be given indefinite oral anticoagulant treatment. Falsely diagnosed patients may be exposed to a high risk of bleeding, without having any benefit of such treatment. False-neg. results have serious consequences for patients suspected for APS because they need long-term anticoagulation to prevent recurrences (7). In this study, the anal. performances of the Hemoclot LA test (Hyphen BioMed), HemosIL Silica Clotting Time (SCT) and HemosIL dRVVT assays (Instrumentation Laboratory) were evaluated on the ACL-TOP analyzer. The anal. LA results of all tests were compared with the LA results obtained from the Sanquin reference laboratory