(a) Donor biopsy at organ procurement. Frozen section of the kidney showing several capillaries distended and filled by recent fibrin thrombi. Similar changes are seen in 75 to 80% of the glomeruli (H&E, 25x). (b) Implantation biopsy (after machine perfusion). In recipient 1, after perfusion of tPA, a few thrombi are seen in some glomeruli; however, the number of affected tufts was less than 50%. (H&E, 25x).