4.2. Blood and Serum Collection

Venous blood was collected by cubital venipuncture from healthy donors who had not taken any antiplatelet drug for two weeks. A 21-gauge butterfly needle was used, and blood was drawn without venous stasis, into either 3 mL vacuum tubes from Dynabyte (Munich, Germany) containing hirudin (final hirudin concentration in blood: 200 U/mL) or S-monovette hirudin tubes from SARSTEDT (Nümbrecht, Germany) (final hirudin concentration in blood: 525 U/mL). The first 2 mL was discarded. The blood was kept at room temperature for 30 min, and measurements were performed subsequently within 2 h after venipuncture.

S-monovette serum gel CAT/7.5 mL tubes (Nümbrecht, Germany) were used for serum preparation for the IgG-specific PF4/polyvinylsulfonate ELISA. After collection, the blood was kept undisturbed at room temperature for 30 min, followed by 1000× g centrifugation for 10 min at 4 °C. The aliquots of serum were stored at −20 °C before measurement.