Low Platelets: HIT, TTP, DIC

• Think dilution, sepsis/DIC, drugs (HIT!), TTP/HUS, immune (ITP), marrow, and liver disease.
• HIT: platelet fall >50% on day 5–14 of heparin exposure (4T score) → STOP heparin, start argatroban/fondaparinux — HIT paradoxically thromboses.
• TTP: MAHA + thrombocytopenia means plasma exchange NOW; no platelets unless life-threatening bleed.
• Transfuse at <10 for prophylaxis, <50 for bleeding or procedures; uremia is about function, not count.
• ISTH 2025 stages DIC as pre-/early/overt with thrombotic vs hemorrhagic phenotypes; ADAMTS13 <10% confirms TTP — never delay plasma exchange for the result.

Diagnostic Pathway for Thrombocytopenia

• Thrombocytopenia
• History and physical examination: current bleeding · drugs · neurological symptoms and signs · gastrointestinal bleeding · recent viral illness · travel history (malaria) · family history · tick exposure · ETOH use · lymphadenopathy · splenomegaly · petechiae · fundal hemorrhage
• Peripheral smear: schistocytes (TTP) · pseudothrombocytopenia (artifact) · spherocytes (hemolysis) · left shift, bands (sepsis) · large platelets (peripheral destruction) · blasts (leukemia) · macrocytosis (liver disease, ETOH)
• Review complete blood count: concomitant cytopenias
• Categorize: decreased platelet production · increased platelet destruction · increased platelet sequestration