Heparin-induced thrombocytopenia
Heparin-induced thrombocytopenia is an immune, prothrombotic drug reaction in which IgG antibodies against platelet factor 4-heparin complexes activate platelets, causing venous and arterial thrombosis alongside a paradoxical falling platelet count. The danger is clotting, not bleeding, so management is to stop all heparin immediately and start a non-heparin anticoagulant while avoiding platelet transfusion and premature warfarin.
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What this article covers
- Overview
Definition: heparin-induced thrombocytopenia (HIT) is an immune, prothrombotic drug reaction in which IgG antibodies form against complexes of platelet factor 4 (PF4) and heparin, cross-link platelet…
- Epidemiology
Exposure-dependent: occurs only in patients recently or currently exposed to heparin, most often hospitalized surgical or critically ill patients receiving UFH for prophylaxis or treatment.
- Risk factors
Unfractionated heparin exposure: the strongest risk factor; risk is several-fold higher than with LMWH, and HIT can occur at any dose, including low-dose prophylaxis.
- Pathophysiology
Antigen formation: heparin binds platelet factor 4, a chemokine released from platelet alpha granules, forming immunogenic PF4-heparin complexes.
- Clinical features
Platelet count fall of 50% or more from baseline, typically with a nadir that rarely falls below 20,000/microL; severe thrombocytopenia is unusual and suggests another or an additional cause.
- Differential diagnosis
Disseminated intravascular coagulation: bleeding and thrombosis together, but with schistocytes, prolonged PT/aPTT, low fibrinogen, and elevated D-dimer from an underlying trigger such as sepsis, not…
- Diagnosis
HIT is confirmed by combining an intermediate-to-high pretest probability on the 4Ts score with a positive laboratory work-up (immunoassay confirmed by a functional assay); no single test alone establishes the diagnosis.
- Management
Stop all heparin immediately once HIT is suspected (intermediate or high 4Ts score), including therapeutic and prophylactic dosing, line flushes, and heparin-coated catheters; do not switch to LMWH…
- Complications
Venous thromboembolism: deep venous thrombosis and pulmonary embolism, the most common thrombotic manifestations.
- Prognosis
Outcome depends on speed of recognition: prompt heparin discontinuation and non-heparin anticoagulation substantially reduce the risk of new thrombosis and death compared with continued heparin exposure.
- Prevention
Minimize unnecessary heparin exposure: favor LMWH or fondaparinux over unfractionated heparin for prophylaxis and treatment when clinically appropriate, since LMWH carries substantially lower HIT risk.
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Related articles
- Thrombocytopenia: an overview
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- Immune thrombocytopenia (ITP)
Immune thrombocytopenia is an acquired isolated thrombocytopenia from antiplatelet autoantibody-mediated destruction plus impaired marrow production, presenting with mucocutaneous bleeding and no splenomegaly. It is a diagnosis of exclusion made by a normal smear and normal other cell lines, and treatment is driven by bleeding risk, starting with glucocorticoids with or without IVIG or anti-D.
- Disseminated intravascular coagulation
Disseminated intravascular coagulation is a secondary, systemic activation of coagulation and fibrinolysis, most often from sepsis, that simultaneously consumes platelets and clotting factors, causing microvascular thrombosis and bleeding. Diagnosis rests on a laboratory constellation, thrombocytopenia, prolonged PT and aPTT, low fibrinogen, and elevated D-dimer, in a predisposing clinical setting, and management centers on treating the underlying trigger while replacing blood components only for active or high-risk bleeding.
- Thrombotic thrombocytopenic purpura (TTP)
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- Antiphospholipid syndrome
Antiphospholipid syndrome is an acquired autoimmune thrombophilia in which antiphospholipid antibodies cause recurrent venous and arterial thrombosis and pregnancy morbidity, paradoxically prolonging the aPTT in vitro while promoting clotting in vivo. Diagnosis requires a qualifying clinical event plus a laboratory antibody confirmed positive on two occasions at least 12 weeks apart, and thrombotic disease is treated with indefinite warfarin rather than a DOAC.
- Platelet disorders
Platelet disorders span a quantitative axis (thrombocytopenia from decreased production, increased destruction, or sequestration) and a qualitative axis (normal-count platelets that fail to adhere or aggregate), plus reactive or clonal thrombocytosis, and all present with mucocutaneous bleeding rather than deep hematomas. Diagnosis starts with a platelet count and smear to exclude pseudothrombocytopenia, adds platelet function testing when the count is normal but bleeding is mucocutaneous, and management is cause-directed.