A small platelet-fibrin thrombus is seen in a glomerular capillary above the arrow. This occurred in a patient with thrombotic thrombocytopenic purpura (TTP). This rare coagulopathy mainly affects kidneys, heart, and brain with small arteriolar thrombi. Acute renal failure can occur. Dr. Rodgers discusses TTP in the coagulation section of the Hematology Organ System.