Heparin-induced thrombocytopenia 69.52

• Heparin-induced thrombocytopenia type I (non-immunological): reduction of platelet count in the early phase of treatment. The decrease in platelet count is significantly less than 50%, but without progression despite continuation of treatment with heparin.
• Heparin-induced thrombocytopenia type II (immunological).

Occurs in about 1-5% of cases during treatment with unfractionated heparin. In treatment with low-molecular-weight heparin, occurrence in < 1% of cases.

• In HIT II, a heparin-induced antibody binds to the IgG-Fc receptor of the thrombocytes and leads to platelet activation. Consecutively, procoagulatory microparticles are generated. In addition, platelet proteins (platelet factor 4) are released, which neutralize free heparin. These platelet proteins bind to heparan sulfate, which is present in the endothelial cell membrane. The complex attaches the autoantibodies and thereby activates the endothelial cells, which increases thrombin formation and finally results in thrombocytopenia. There is a risk of loss of extremities through thrombotic events. There is also a potential danger to the patient's life!
• The occurrence of HIT II depends on the duration and dose of the heparin treatment as well as on the molecular size of the active substance. Longer-chain, unfractionated heparin has a two to three times higher risk of HIT II than low molecular weight heparin.

• Initially succulent, red-blue to blue-black, painful spots that can develop into extensive plaques. Formation of hemorrhagic blisters possible.
• In about 40% of cases, arterial or venous vessel occlusion (also known as white-clot syndrome ) occurs.
• Note: the HIT can be estimated by the 4T-score: thrombocytopenia, timing, thrombosis and other causes of thrombocytopenia.

• Detection of antibodies against platelet factor 4-heparin complex by ELISA.
• Performance of a HIPA test.
• Regular laboratory controls.

• Heparin-induced thrombocytopenia type I: self-limiting course with continuation of heparin therapy; spontaneous regression of thrombocytopenia within a few days
• Heparin-induced thrombocytopenia type II: immediate discontinuation of heparin; alternatively, if there is an indication for anticoagulation, treatment should be continued with either the heparinoid danaparoid sodium (Orgaran) or the recombinant hirudin preparation lepirudin (refludan; 0.4 mg/kg bw as a bolus, then continuous infusion 0.15 mg/kg bw).
• If necessary, argatroban (synthetically produced direct thrombin inhibitor) initially 0.5-2 µg/kg bw/min. i.v.; regular laboratory checks!

Remember! Any platelet drop to less than 50% of the initial value or to absolute values < 100,000 platelets/µl must always be considered as heparin-induced thrombocytopenia type II until proven otherwise!

1. Greinacher A et al (2003) Heparin-induced thrombocytopenia. Dtsch Ärztebl 100: 2220-2229
2. Greinacher A et al (1991) A rapid and sensitive test for diagnosing heparin-associated thrombocytopenia. Thromb haemost 66: 734-736
3. Helbig D et al (2007) Skin and mucosal ulcerations in heparin-induced thrombocytopenia (HIT II). Dermatologist 58: 774-778
4. Warkentin TE et al (2006) Gender imbalance and risk factor interactions in heparin-induced thrombocytopenia. Blood 108: 2937-2941