Schistocytes, Thrombocytopenia, and a Pending ADAMTS13
A 34-year-old woman presents with 3 days of confusion, petechiae, and fatigue. She is not pregnant and has no diarrhea. Labs: Hb 8.1 g/dL, platelets 14 ×10^9/L, WBC 9.2 ×10^9/L, LDH 1,200 U/L, haptoglobin <10 mg/dL, creatinine 1.0 mg/dL, total bilirubin 3.1 mg/dL indirect, PT/INR 1.0, aPTT 28 s, fibrinogen 320 mg/dL. Peripheral smear shows 3% schistocytes and no platelet clumps. ADAMTS13 activity is pending and will return in 48 hours. The blood bank has plasma exchange available but only one slot tonight; the intensivist asks whether to start steroids and plasma exchange empirically or wait for the result.
1. What is the most likely diagnosis, and what should be done in the next hour?
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The picture is most consistent with immune thrombotic thrombocytopenic purpura (TTP): severe thrombocytopenia, microangiopathic hemolysis with schistocytes, neurologic symptoms, and normal PT/aPTT/fibrinogen. A high PLASMIC score supports this. Do not wait for ADAMTS13. Start urgent plasma exchange with fresh frozen plasma and corticosteroids, and involve apheresis and hematology immediately. Avoid platelet transfusion unless there is life-threatening bleeding, because it may worsen microthrombosis. Monitor neurologic status, renal function, and hemolysis markers. If plasma exchange cannot start immediately, transfer to a center that can provide it.
2. How do the coagulation results and smear findings argue against DIC and HUS in this patient?
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DIC usually prolongs PT and aPTT, lowers fibrinogen, and raises D-dimer; this patient has normal coagulation studies and normal fibrinogen, which makes DIC unlikely. HUS typically causes prominent renal failure, often after diarrheal illness, and schistocytes may be present, but creatinine here is normal and there is no diarrheal prodrome. The 3% schistocytes are compatible with TTP and do not exclude it. Normal coagulation studies do not rule out TTP; they help exclude DIC. Pregnancy-associated HELLP is also unlikely because she is not pregnant.
3. ADAMTS13 returns at 18%. How do you interpret this, and does it change management?
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An activity of 18% is not diagnostic of immune TTP, which generally requires <10% activity with an inhibitor or low ADAMTS13 antigen. Values between 10% and 20% are indeterminate and can occur in other thrombotic microangiopathies, liver disease, or assay variability. If the clinical picture remains typical and the patient is responding to plasma exchange, continue treatment and repeat ADAMTS13 after additional exchanges. Do not stop plasma exchange solely because the first value is 18%. Reassess for alternative diagnoses, including complement-mediated TMA, if the response is poor.