<s>[INST] context: Thrombotic thrombocytopenic purpura (TTP) is a rare disorder of unknown etiology. It is characterized by an increased bleeding time but a decreased platelet count. It causes purpura, fever, renal failure, microangiopathic hemolytic anemia, and microthrombi, frequently in young women. Elevated indirect bilirubin and high LDH are characteristic, as are schistocytes in the blood smear, renal dysfunction, and neurologic and systemic symptoms. Negative findings impoant to rule out similar conditions include a negative Coombs test and absence of fibrin split products. TTP is thought to be initiated by endothelial injury, which releases ceain procoagulant materials into the circulation, causing platelet aggregation. This condition may be precipitated by pregnancy or use of estrogens. Autoimmune hemolytic anemia can cause anemia and an elevated indirect bilirubin, but generally produces only mild symptoms, is not associated with thrombocytopenia, and does not cause fragmentation of red blood cells on the peripheral smear. The negative Coombs test argues against autoimmune hemolytic anemia. Disseminated intravascular coagulation can be differentiated from TTP because of abnormal coagulation tests. In DIC, microangiopathic hemolysis is also present, but the prothrombin time (PT) and paial thromboplastin time (PTT) are prolonged, fibrinogen levels are reduced, and fibrin split products are elevated. Hemolytic-uremic syndrome is not significantly different from TTP. The two conditions, in fact, are considered manifestations of the same pathogenetic spectrum. However, the vascular bed of the CNS is not involved in HUS. Thus, mental status changes are not pa of the clinical picture of HUS. [/INST] question: A 47-year-old woman is brought to the hospital by her husband with fever, headache, confusion, and jaundice for 1 week. She underwent a hysterectomy 2 months ago and began estrogen replacement therapy recently. On admission, her temperature is 38.7 C (102 F), blood pressure is 140/90 mm Hg, Pulse is 98/min, and Respiratory rate is 20/min. She appears disoriented to time and place. Physical examination reveals jaundiced sclerae and skin, purpura on the trunk, and bleeding gums. Her platelet count is 25,000/mm3, hematocrit is 24%, and creatinine is 4.9 mg/dL. Lactate dehydrogenase (LDH) and indirect bilirubin are elevated. Coagulation tests are within normal limits, but the bleeding time is increased; fibrin-split products and Coombs test are negative. A peripheral blood smear shows schistocytes, helmet-shaped cells, and cells with a triangular shape. Which of the following is the most likely diagnosis? | options: A: Autoimmune hemolytic anemia B: Disseminated intravascular coagulation (DIC) C: Hemolytic-uremic syndrome (HUS) D: Thrombotic thrombocytopenic purpura (TTP) | answer: D </s>