Laboratory tests for the antiphospholipid syndrome: current concepts

There is increased scientific interest in the diagnosis of the antiphospholipid syndrome (APS), as therapeutic interventions can lead to substantial improvement in clinical outcome. As the clinical features of APS are far from specific, a sound laboratory method is needed to support or exclude the diagnosis. Two methods are currently used for the diagnosis of APS: (1) ELISA-based immunoassays for the detection of anticardiolipin (aCL) antibodies; and (2) clotting assays for determination of the lupus anticoagulant (LA). However, the first method is limited by a low specificity, and the second by low sensitivity. Furthermore, for both methods standardisation is unsatisfactory. Therefore, a number of new assays have been proposed as alternative or supplementary to aCL and LA tests. These include the anti-beta-2-glycoprotein I or antiprothrombin ELISAs, an ELISA utilising a phospholipid mixture, clotting assays with varying activators and assays utilising chromogenic substrates. This review presents a brief outline of APS, the autoantibodies associated with this syndrome, the basic principles of the standard assays used and a description of newer methods currently being validated.