A 35-year-old woman presents with hemolytic anemia, thrombocytopenia, and renal failure following a gastroenteritis. Blood film shows schistocytes. Serum LDH is markedly elevated. ADAMTS13 activity returns at 75% (normal). Stool culture grows E. coli O157:H7. The diagnosis is Shiga toxin-associated HUS. Unlike TTP, ADAMTS13 in typical HUS is:
- A Normal or mildly reduced — distinguishes it from TTP ✓
- B Severely deficient (<10%) — indistinguishable from TTP
- C Absent in all HUS subtypes
- D Absent only in aHUS (atypical HUS) due to complement dysregulation
Correct answer: A. Normal or mildly reduced — distinguishes it from TTP
Explanation
ADAMTS13 activity distinguishes TTP from HUS: TTP is characterised by severe ADAMTS13 deficiency (<10%), caused by autoantibodies (acquired TTP) or genetic mutations (congenital TTP/Upshaw-Schulman). Typical (Shiga toxin-associated) HUS and atypical HUS (complement-mediated) both have normal or mildly reduced ADAMTS13, as the pathogenesis involves direct endothelial injury (Stx) or complement activation, not VWF cleavage deficiency.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.