[Recurrent thromboembolisms despite full anticoagulation in a patient with antiphospholipid syndrome]

We report on a female patient with confirmed secondary antiphospholipid syndrome (APS) due to underlying systemic lupus erythematosus (SLE). Despite a thromboplastin time within the normal range (international normalized ratio, INR) under treatment with a vitamin K antagonist (VKA), a recurrent thrombotic event occurred, this time as pulmonary embolism due to bilateral deep vein thrombosis. Despite an INR value in the therapeutic range, clotting factors II, VII, IX and X were found to be insufficiently decreased suggesting inefficient anticoagulation. Thus, the anticoagulation regimen was changed to the direct oral anticoagulant dabigatran. This case demonstrates that the INR in APS patients may be artificially prolonged in rare cases, despite a normal activated partial thromboplastin time (aPTT) and cannot be used for monitoring VKA anticoagulant therapy. Suspicion of ineffective anticoagulation despite VKA therapy should prompt measurement of the individual clotting factors.