False-negative or false-positive: Laboratory diagnosis of lupus anticoagulant at the time of commencement of anticoagulant

摘要

'Lupus anticoagulant' (LA) is the term that has evolved for the in vitro phenomenon of prolonging clotting times in laboratory tests. The LA test is an indirect reflection of interference of a given plasma upon the phospholipid in the reagent. Demonstration of its presence in plasma is an important tool in the diagnosis of anti-phospholipid antibody syndrome (APS) [1]. In external Quality Assurance Programmes (QAP), plasmas that are strongly positive for LA are accurately identified by almost all laboratories. However, the percentage of false-positive or false-negative diagnoses increases markedly when plasmas containing weak LA are tested. The corollary of this is that either over-diagnosis of LA (false positive) can occur; in turn inappropriately subjecting the patient to long-term anticoagulation [2] or under-diagnosis (false negative) may arise potentially increasing the likelihood of recurrent throm-botic events [3].