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Heparin-Induced Thrombocytopenia

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Overview

Heparin-induced thrombocytopenia (HIT) is characterised by thrombocytopenia secondary to the administration of heparin. IgG antibodies bind to heparin/platelet factor 4 complexes leading to the activation of platelets and induce an initially hypercoagulable state. The platelets then get consumed leading to a state of thrombocytopenia.

Classical History

A 50-year-old woman has a right-leg deep vein thrombosis 3 days after being treated for acute coronary syndrome with IV heparin.

Investigations before admission:

Platelets:200 x 109/L(150 – 450 x 109/L)

Investigations after admission:

Platelets:75 x 109/L(150 – 450 x 109/L)

Differential Diagnoses

Thrombotic thrombocytopenic purpura

  • Patients usually have neurological abnormalities due to micro-emboli
  • HIT assay test negative for HIT antibodies
  • Peripheral blood film shows microangiopathic haemolytic anaemia with schistocytes

Investigations

All patients

  • Full blood count (FBC):
    • Shows thrombocytopenia
  • HIT antigen assay:
    • Positive for HIT antibodies – this alone is not sufficient for diagnosis
  • HIT functional assay:
    • Positive results confirm HIT

Management

All patients

  • 1st-line: stop heparin (including LMWH) and replace the anticoagulant with an alternative e.g. argatroban, danaparoid, or direct oral anticoagulants (DOACs)
  • Patients should notify healthcare workers that they have had HIT

Complications

  • Venous gangrene
  • Limb amputation
  • Bleeding
  • Arterial or venous thrombosis

Prognosis

  • Platelets usually return to normal within 1 week

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