Hemolytic uremic syndrome is classically characterized by which triad?

• A. Microangiopathic hemolytic anemia, thrombocytopenia, acute renal failure
• B. Leukocytosis, fever, rash
• C. Hypotension, tachycardia, syncope
• D. Anemia, leukopenia, hepatomegaly

Answer: (A)

Hemolytic uremic syndrome presents with damage to small vessels that leads to red cell destruction, low platelets, and kidney injury.

The first component is microangiopathic hemolytic anemia, where red blood cells are fragmented as they pass through damaged, obstructed microvasculature. This produces schistocytes on a blood smear and labs showing elevated LDH with decreased haptoglobin, reflecting hemolysis.

The second component is thrombocytopenia, caused by platelets being consumed in the forming microthrombi within the small vessels.

The third component is acute renal failure, resulting from impaired microcirculation in the kidneys due to those same microthrombi, leading to reduced urine output and rising BUN/creatinine.

These three elements together—microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure—define the classic triad of HUS. Other options describe different syndromes (for example, sepsis-like presentations, shock states, or hepatosplenomegaly) and do not fit this triad.