CSPα^−/− mice have defective thrombosis under flow at low shear rates. A BioFlux microfluidics system was used to examine thrombus formation at a low shear rate of 10 dyn/cm² (A-E) or high shear rate of 35 dyn/cm² (F-J) over immobilized collagen for CSPα^+/+, CSPα^+/−, and CSPα^−/− mice. Historic data from the laboratory for Unc13d^Jinx mice was added for reference. (A) Representative images of thrombus formation were taken for CSPα^+/+ (n = 5), CSPα^+/− (n = 7), and CSPα^−/− (n = 4) mice at low shear rates during postperfusion washing. Quantitative analysis of platelet surface area coverage (B), morphological score (C), contraction score (D), and multilayer score (E) were measured at a low shear rate. (F) Representative images of thrombus formation were taken for CSPα^+/+ (n = 5), CSPα^+/− (n = 6), and CSPα^−/− (n = 5) mice at high shear rates during postperfusion washing. Quantitative analysis of platelet surface area coverage (G), morphological score (H), contraction score (I), and multilayer score (J) were measured at the high shear rate. Scaled from 0 (no thrombus formation) to 5 (fully formed contracted and multilayered thrombi) for morphological score. Contraction and multilayer scores were scaled from 0 (no thrombus formation) to 3 (fully formed contracted and multilayered thrombi). Statistical analyses were performed using individual values and the Kruskal-Wallis multiple comparison test and corrected using the Dunn multiple comparison test. The P values are indicated. Scale bar, 50 μm.