Addition of cardiolipin in APTT-based LAC assay. Plasmas of 2 patients were diluted 1:1 with normal pool plasma and incubated with different concentrations of cardiolipin and reagent (Diagnostica Stago). As a reference we performed the same assay with normal pool plasma. An LAC was characterized as β₂-GPI dependent when the ratio of patient plasma divided by normal plasma decreased by at least 0.05 at 25 μM cardiolipin compared with no addition of cardiolipin. Coagulation was initiated by the addition of CaCl₂, and clotting time was measured.