Syk^{R41Afl/fl;PF4-Cre} mice have a mild thrombosis defect. (A) Anticoagulated whole blood from wild-type (WT) and Syk^{R41Afl/fl;PF4-Cre} (R41A) mice was labeled with DiOC₆ prior to flow over capillary tubes coated with collagen (100 μg/ml) at 1000 s⁻¹ for 4 minutes. Fluorescence thresholding was used to calculate surface area coverage (n = 3, ***P < .005). (B) FeCl₃ (20%) was used to induce an injury in mesenteric arterioles. Platelets were labeled with DyLight488-labeled α-GPIbβ antibody. Thrombus formation was monitored for 40 minutes. Time to the initiation of a thrombus was measured (i), as was time to vessel occlusion (ii). If a vessel did not occlude within 40 minutes, the experiment was terminated (n ≥ 11, **P < .01). (C) Mice were anesthetized with isoflurane followed by removal of 3 mm of tail. Blood loss was monitored for up to 20 minutes or until 15% of total blood volume was lost (n = 6, *P < .05).