Strong lupus anticoagulant (LA) as a cause for prolonged prothrombin time (PT), activated partial thromboplastin time (APTT) and abnormally low intrinsic factor (IF) levels

Abstract

We report the case of a previously healthy 53-year-old male who presented with an incidental finding of both prolonged PT (57 seconds) and APTT (41 seconds) whilst being investigated for acute abdominal pain. There was no personal or family history of bleeding or thrombosis. Partial correction of both PT and APTT was demonstrated on mixing studies, with presence of heparin excluded. Intrinsic factor assays showed universal reduction, with Bethesda assay failed to identify an inhibitor. Extrinsic factors and von Willebrand assays were normal. LA testing showed a moderate strength LA, confirmed by a strongly positive IgM anticardiolipin (ACL) and moderately positive IgG ACL antibody. PT is normally relatively insensitive to LA. Nevertheless, falsely increased PT has been reported, likely from interference of LA with the phospholipid component of the PT reagent, particularly where recombinant tissue factor and purified phospholipids are used. This can result in difficulties with INR monitoring in warfarinised patients. This case also illustrates how the presence of a potent LA can also interferes with factor assays interpretations. Therefore all diagnostic laboratories should develop a robust policy to detect and monitor this unique group of patients.