S100A9 and Stroke: S100A9 protein was present in all thrombi analyzed and quantification of thrombus constituents revealed that stroke thrombi contained on average 12.8% (IQR 1.34–28.89) red blood cells, 15.05% (4.84–26.65) platelets, 0.62% (0.35–1.17) leukocytes, and 3.52% (1.17–6.68) S100A9.