Heparin Induced Thrombocytopenia Anticoagulation

Heparin-induced thrombocytopenia is an immune reaction to heparin and platelet factor 4 that causes a platelet fall and a high risk of clotting. Suspect it when platelets fall by over 50% or to under 100 x 10^9/L, usually 5 to 14 days after starting heparin (sooner with recent exposure), with or without a new clot or skin necrosis at injection sites.

Pre-test score. Use the 4Ts score (thrombocytopenia, timing, thrombosis, other causes). A low score excludes it; an intermediate or high score needs immediate action and a laboratory test (platelet factor 4 antibody immunoassay, functional assay).

First actions. Stop all heparin (unfractionated, low molecular weight, flushes, heparin-coated lines) and start a non-heparin anticoagulant at once, without waiting for results.

• Argatroban 2 mcg/kg/min by intravenous infusion, adjusted to aPTT 1.5 to 3 times baseline (maximum 10 mcg/kg/min). Start at 0.5 to 1.2 mcg/kg/min in liver impairment, heart failure, multi-organ failure or after cardiac surgery.
• Bivalirudin 0.15 mg/kg/h intravenously (adjusted to aPTT 1.5 to 2.5 times baseline), used in kidney failure and cardiac surgery, under specialist direction.
• Fondaparinux subcutaneously once daily by weight: under 50 kg 5 mg, 50 to 100 kg 7.5 mg, over 100 kg 10 mg. Avoid if creatinine clearance is under 30 mL/min. Off-label but widely used.
• Danaparoid where available, by weight-based bolus and infusion under specialist direction.
• Direct oral anticoagulants after platelet recovery or in stable patients: rivaroxaban 15 mg twice daily for 21 days then 20 mg once daily, or apixaban 10 mg twice daily for 7 days then 5 mg twice daily.
• Warfarin: start only after platelets have recovered to over 150 x 10^9/L, and overlap with a non-heparin drug for at least 5 days and until INR is in range for 24 hours. Do not start warfarin in acute heparin-induced thrombocytopenia (risk of venous limb gangrene); if it has been given, reverse with vitamin K.

Duration. Heparin-induced thrombocytopenia with thrombosis: 3 months. Isolated disease: continue until platelets recover over 150 x 10^9/L, and many clinicians continue for 4 weeks.

Platelet transfusion. Avoid unless there is major bleeding.

Kidney impairment. Argatroban and bivalirudin dose by clearance and drug. Avoid fondaparinux when clearance is under 30 mL/min.

Liver impairment. Lower argatroban starting dose; avoid in severe failure unless monitored.

Pregnancy. Fondaparinux 2.5 mg or danaparoid under specialist direction; avoid warfarin and direct oral anticoagulants.

Cardiac surgery or dialysis. Bivalirudin or specialist plan.

Special groups. In East Africa, argatroban, bivalirudin and danaparoid are rarely available, so fondaparinux and, after stabilisation, a direct oral anticoagulant are the usual options. Avoid all future heparin and record the allergy.

Monitoring. Platelet count daily until recovery, aPTT 2 hours after any argatroban or bivalirudin change and then daily, and limb and skin checks. Look for new thrombosis.

Referral and escalation. Seek haematology review urgently for every suspected or confirmed case, and vascular or surgical review for limb ischaemia or skin necrosis.

Stopping. Stop the non-heparin anticoagulant at the end of the planned duration once platelets are stable, and keep heparin avoided for life, except in cardiac surgery with specialist plan after antibodies clear.