Heparin-induced thrombocytopenia

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Background

  • Pathologic activation / consumption of platelets due to antibodies against heparin-platelet complex
  • Despite the low platelet count, the patient is actually hyper-coagulable and bleeding is unusual. The activated platelets cause blood clot formation and the platelet count falls because the platelets are bound in clots.
  • Can be caused by unfrationated or LMWH (10x common in the former)
  • Occurs in 0.5-5% of patients treated with heparin[1]
  • Thrombosis occurs in 35-75% of patients ; 20-30% die within 1 month[1]

Type 1 HIT

Occurs within the first 48 hours after heparin use with an initial drop in platelet count due to direct effect of heparin on platelet activation. The platelet count normalizes in a few days with continued heparin treatment.[2]

Type 2 HIT

An immune-mediated process which typically occurs 5-10 days after exposure to heparin complicated by thrombosis. [2]

Clinical Features

Symptoms usually begin 5-10 days after initiation of heparin or can begin within hours if there are already preexisting circulating antibody from prior sensitization

Delayed Symptoms

  • >50% decrease in plt count (median nadir is ~60K; rarely <20K)
  • DVT or PE
  • Cerebral vein or adrenal vein thrombosis
  • Limb arterial occlusion
  • CVA
  • MI
  • Skin necrosis

Immediate Symptoms

DDX

Diagnosis

  • Serotonin release assay (SRA) = gold standard
  • Anti-PF4 plus SRA has combined senativity of 99% [3]
  • Positivity determined by optical density (OD) reported w/ assay (same concept as a titer)
    • OD <1 = <5% chance of HIT
    • OD 1.4 = 50% chance of HIT
    • OD >2 = 90% chance of HIT

Treatment

  1. Discontinue all heparin products
  2. Do not give platelts (may precipitate thrombosis)
  3. Start anticoagulation with no heparin based compound such as a direct thrombin inhibitor [lepirudin (unless renal failure), argatroban (unless hepatobiliary disease), bivalirudin] or direct Xa inhibitor (fondaparinux, danaparoid)
  4. Avoid warfarin until platelets >100K-150K

Dispostion

  • Admit to medicine with a hematology consult

See Also

Source

  1. 1.0 1.1 Lovecchio F. Heparin-induced thrombocytopenia. Clin Toxicol (Phila). 2014 Jul;52(6):579-83
  2. 2.0 2.1 Warkentin T. et al. Heparin-induced thrombocytopenia: recognition, treatment, and prevention: the Seventh ACCP Conference on Antithrombotic and Thrombolytic Therapy. Chest. 2004 Sep;126(3 Suppl):311S-337S
  3. Warkentin TE, et al. Chest. 2008;133(6 Suppl):340S-380S.