A 29-year-old primigravida at 26 weeks presents with BP 164/108 mmHg, platelet count 28,000/µL, hemoglobin 8.2 g/dL with schistocytes on peripheral smear, LDH 1,800 U/L, and severe right upper quadrant pain. Creatinine is 1.1 mg/dL. Neurologic exam is normal. Which additional finding would BEST differentiate thrombotic thrombocytopenic purpura (TTP) from severe pre-eclampsia/HELLP?
- A Urine protein/creatinine ratio 0.45
- B Serum uric acid 8.2 mg/dL
- C ADAMTS13 activity less than 10% of normal ✓
- D Elevated indirect bilirubin with reticulocytosis
Correct answer: C. ADAMTS13 activity less than 10% of normal
Explanation
TTP and severe pre-eclampsia/HELLP both present with microangiopathic hemolytic anemia and thrombocytopenia. ADAMTS13 activity severely reduced to less than 10% is diagnostic of TTP (immune-mediated). In HELLP, ADAMTS13 is typically normal or mildly reduced but never severely deficient. Elevated uric acid, proteinuria, and hemolysis markers occur in both conditions and do not differentiate them.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.