La 1 screening and la 2 confirmation reagents

STA-Coag lyophilized control citrated normal human plasma (NP; Diagnostica Stago, Paris, France) was reconstituted with distilled water and allowed to stand at RT for 30 minutes before testing. The LA 1 screening and LA 2 confirmation reagents (Siemens Healthcare Pty Ltd, Victoria, Australia) were reconstituted with distilled water, left at RT for 15 minutes, and then prewarmed at 37°C prior to testing. The LA testing was performed according to the manufacturer’s instructions (Siemens Healthcare Pty Ltd). Briefly, NP was incubated for 10 minutes with different commercially available anti-β₂GP1 antibodies (final concentrations 5, 2.5, and 1.25 μg/mL). Siemens LA 1 screening reagent (100 μL) containing Russell’s viper venom and phospholipids was added to 100 μL of plasma spiked with antibodies. Antibody-free NP and high and low LA controls (100 μL) were also assessed. All clotting times were measured using a STart coagulation analyzer (Diagnostica Stago, Paris) in triplicate. Samples with a “screen” (S) clotting time greater than 44 seconds were retested with LA 2 confirmation reagent (containing higher amounts of phospholipid) to obtain a “confirm” (C) clotting time. The normal ratio of S/C was 0.8 to 1.2. The ratios for weak, moderate, and strong LA activities are 1.2 to 1.5, 1.5 to 2.0, and greater than 2, respectively.