A 5-year-old child develops the sudden onset of bloody diarrhea, vomiting of blood, hematuria, and renal failure following a flulike gastrointestinal illness. The blood urea nitrogen (BUN) level is markedly increased, but fibrin degradation products and blood clotting times are within normal limits. A peripheral blood smear reveals poikilocytes, schistocytes, and a decrease in the number of platelets. No fever or neurologic symptoms are present. What is the best diagnosis for this patient?

**Core Concept**
Hemolytic-uremic syndrome (HUS) is a disorder characterized by the triad of microangiopathic hemolytic anemia, acute kidney injury, and thrombocytopenia, often triggered by Shiga toxin-producing bacteria such as E. coli O157:H7.

**Why the Correct Answer is Right**
The patient's presentation of bloody diarrhea, vomiting of blood, hematuria, and renal failure following a gastrointestinal illness is suggestive of HUS. The peripheral blood smear findings of poikilocytes, schistocytes, and thrombocytopenia are consistent with microangiopathic hemolytic anemia, which is a hallmark of HUS. The normal fibrin degradation products and blood clotting times indicate that the coagulopathy seen in HUS is not due to disseminated intravascular coagulation (DIC). The absence of fever and neurologic symptoms helps to rule out other causes of acute kidney injury.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the clinical presentation and laboratory findings of HUS. Thrombotic thrombocytopenic purpura (TTP) typically presents with fever, neurologic symptoms, and renal failure, which are not present in this case.

**Option B:** This option is incorrect because it does not account for the gastrointestinal symptoms and the normal fibrin degradation products.

**Option C:** This option is incorrect because it does not accurately describe the laboratory findings of HUS.

**Option D:** This option is incorrect because it does not account for the renal failure and the normal blood clotting times.

**Clinical Pearl / High-Yield Fact**
HUS is a classic example of a "microangiopathic" disorder, characterized by the formation of small blood clots within the microvasculature, leading to hemolytic anemia, renal failure, and thrombocytopenia. It is often triggered by Shiga toxin-producing bacteria, such as E. coli O157:H7, which can cause a flulike gastrointestinal illness.

**Correct Answer: C. Hemolytic-uremic syndrome (HUS)**

✓ Correct Answer: B. Hemolytic-uremic syndrome (HUS)