dRVVT is more sensitive than KCT or TTI for detecting lupus anticoagulant activity of anti-beta 2-glycoprotein I autoantibodies

Anti-beta(2)-glycoprotein I (beta(2)-GPI) antibodies behave as classical Lu pus Anticoagulants (LA), as they inhibit phospholipid-dependent coagulation reactions and their activity disappears in the presence of excess exogenou s phospholipids (PLs). We have recently shown that a certain amount of PLs in the dilute Russell Viper Venom Time (dRVVT) test system is required to e xpress LA activity of anti beta(2)-GPI antibodies. We have now extended thi s observation to two other tests, i.e., Kaolin Clotting Time (KCT) in which PLs are not added, and Tissue Thromboplastin Inhibition test (TTI) in whic h PLs are extremely diluted. In fact, affinity-purified antibody preparatio ns From 5 patients with antiphospholipid syndrome did not express or only w eakly expressed anticoagulant activity in both tests; the mean ratios of co agulation times obtained with purified antibodies and that of control buffe r were 1.11 and 1.0 for KCT and TTI, respectively. On the contrary, the mea n ratios in dRVVT were 1.31 and 1.49 at a PLs dilution of 1:8 and 1:64, res pectively. Therefore, the presence of LA activity due to autoantibodies to beta(2)-GPI is characterized by a positive dRVVT and negative or only weakl y positive KCT and TTI.