Laboratory diagnosis of lupus anticoagulants

Abstract

Recently the significance of a finding of iupus anticoagulant (LA) in a patient has changed. Previously regarded merely as a laboratory curiosity LA are now recognised as potential risk factors for thrombosis and in women appear to be responsible for recurrent fetal loss. Though it was initially suggested that LA and anticardiolipin antibodies (aCL) may be identical phosphotipid-binding immunoglobulins, more recent studies have shown the correlation between aCL and LA to be incomplete. Many patients have raised aCL without LA though the reverse situation is less common. The most sensitive screening tests for LA utilise low concentration of phospholipid for example in the kaolin clotting time, the dilute Russell’s viper venom test or the dilute tissue thromboplastin inhibition test. Prolongation of such tests by LA can usually be corrected by the addition of “excess” procoagulant phospholipid Conversely LA are not corrected by mixing with normal plasma. A LA test appropriate for a particular purpose should be selected. Thus hospital patients often present with other coagulation complications, e.g. anticoagulants, or liver disease, and the LA defect needs to be carefully distinguished from conditions likely to contribute to bleeding. Thus greater specificity is required for this group whereas sensitivity is the most important consideration for detecting LA in otherwise normal females being investigated e.g.for recurrent miscarriages. It is important to carry out LA tests on correctly processed samples particularly avoiding platelet activation which may ‘bypass” the LA defect.