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TMA Differential ADAMTS13 — ESENeph MCQ

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ModerateAcute Kidney InjuryTMA Differential ADAMTS13ESENeph

A 50-year-old man presents with AKI and findings suggestive of thrombotic microangiopathy (TMA): schistocytes, elevated LDH, low haptoglobin, thrombocytopenia. What is the first critical investigation to differentiate TTP from other causes of TMA?

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Correct answer: C — ADAMTS13 activity level – if <10%, this confirms TTP; if >10%, consider aHUS, STEC-HUS, secondary TMA, or malignant hypertension

ADAMTS13 activity is the pivotal first test in the TMA differential: activity <10% is diagnostic of TTP (deficiency of the von Willebrand factor-cleaving protease). If >10%, TTP is excluded and other causes must be evaluated: STEC-HUS (stool culture, Shiga toxin), aHUS (complement studies, genetic testing), secondary TMA (malignant hypertension, scleroderma renal crisis, HELLP, DIC, drugs, malignancy). This result guides immediate treatment: TTP requires urgent plasma exchange + Caplacizumab; aHUS requires Eculizumab; STEC-HUS is supportive.

Reference: ISTH 2020 – TMA Guideline; BSH 2023 – TMA