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.

Unexplained thrombocytopenia

First tests: Full blood count, Peripheral blood film, PT/INR, aPTT and fibrinogen, Sodium, potassium, bicarbonate, urea and creatinine.

Only if indicated: Citrated platelet count, LDH, bilirubin, haptoglobin and reticulocytes, HIT testing guided by 4Ts.

Repeat monitoring: Full blood count.

Suspected heparin-induced thrombocytopenia

First tests: 4Ts pretest probability assessment, Full blood count.

Only if indicated: PF4/heparin immunoassay, Functional platelet-activation assay, Venous compression ultrasound.

Repeat monitoring: Full blood count.

Suspected TTP / thrombotic microangiopathy

First tests: Full blood count, Peripheral blood film, LDH, bilirubin, haptoglobin and reticulocytes, Sodium, potassium, bicarbonate, urea and creatinine, ADAMTS13 activity and inhibitor/antibody.

Only if indicated: PT/INR, aPTT and fibrinogen, High-sensitivity cardiac troponin.

Repeat monitoring: Full blood count.

DIC / major bleeding coagulopathy

First tests: Full blood count, PT/INR, aPTT and fibrinogen, Blood group and crossmatch, Sodium, potassium, bicarbonate, urea and creatinine.

Only if indicated: D-dimer / fibrin degradation products, Viscoelastic testing, Ionized calcium.

Repeat monitoring: Full blood count, PT/INR, aPTT and fibrinogen.

• Diagnostic Pathway for Thrombocytopenia