What is the diagnosis and treatment for Heparin (unfractionated heparin) induced thrombocytopenia (HIT)?

From the Guidelines

Heparin-induced thrombocytopenia (HIT) is a rare but potentially lethal side effect of heparin administration, and its diagnosis and treatment require immediate attention. The diagnosis of HIT is based on clinical suspicion, and biological confirmation is necessary in all cases, but should not delay the discontinuation of heparin and the initiation of alternative anticoagulation therapy 1.

Diagnosis of HIT

• HIT is characterized by a decrease in platelet count, usually by more than 50%, and the presence of anti-platelet factor 4 (PF4) antibodies 1.
• The diagnosis of HIT should be suspected in patients who develop thrombocytopenia after heparin administration, particularly if they have a history of recent thrombosis or if they are at high risk of thrombosis 1.
• The 4T score is a useful tool to estimate the pre-test probability of HIT, and it takes into account the degree of thrombocytopenia, the timing of thrombocytopenia, the presence of thrombosis, and the absence of other causes of thrombocytopenia 1.

Treatment of HIT

• Discontinuation of heparin therapy is the first step in the management of HIT, and it should be done immediately if HIT is suspected 1.
• Alternative anticoagulation therapy should be initiated as soon as possible, and the options include direct thrombin inhibitors such as argatroban and bivalirudin, or heparinoids such as danaparoid 1.
• Direct oral anticoagulants (DOACs), such as rivaroxaban and apixaban, may be considered as alternative anticoagulants in patients with HIT, although their use is not yet widely established 1.
• Intravenous immunoglobulin (IVIg) may be considered in patients with spontaneous or persistent autoimmune HIT, or in patients who are refractory to treatment 1.

Special Considerations

• Patients with a history of HIT should be carefully evaluated before receiving heparin again, and alternative anticoagulants should be considered 1.
• In patients with HIT who require cardiovascular surgery or percutaneous cardiovascular intervention, alternative anticoagulants should be used, and the procedure should be performed as soon as possible after the diagnosis of HIT is made 1.

From the FDA Drug Label

Heparin-induced thrombocytopenia (HIT) is a serious antibody-mediated reaction. HIT occurs in patients treated with heparin and is due to the development of antibodies to a platelet Factor 4-heparin complex that induce in vivo platelet aggregation HIT may progress to the development of venous and arterial thromboses, a condition referred to as heparin-induced thrombocytopenia with thrombosis (HITT). If the platelet count falls below 100,000/mm3 or if recurrent thrombosis develops, promptly discontinue heparin, evaluate for HIT and HITT, and, if necessary, administer an alternative anticoagulant.

The diagnosis of Heparin-Induced Thrombocytopenia (HIT) is made when the platelet count falls below 100,000/mm3 or if recurrent thrombosis develops. The treatment for HIT is to:

• Promptly discontinue heparin
• Evaluate for HIT and HITT
• If necessary, administer an alternative anticoagulant 2

From the Research

Diagnosis of Heparin-Induced Thrombocytopenia (HIT)

• The diagnosis of HIT is based on a combination of clinical probability and laboratory tests, including the 4Ts score 3, 4, 5.
• The 4Ts score is used to identify patients at increased likelihood of HIT, and further evaluation is recommended for patients with an intermediate or high probability score 4, 5.
• Laboratory tests, such as immunoassay and functional assay, are used to confirm or refute the diagnosis of HIT 4, 5.
• A relative reduction in platelet count of 50% or more, occurring within 5-14 days after initiation of heparin therapy, is a key feature of HIT 6.

Treatment of Heparin-Induced Thrombocytopenia (HIT)

• Immediate discontinuation of heparin is essential in the treatment of HIT 3, 4, 5, 7.
• Alternative anticoagulation, such as nonheparin anticoagulants, should be initiated to prevent further thrombotic complications 3, 4, 5, 7.
• The selection and use of nonheparin anticoagulation should be based on patient characteristics and institutional resources 5.
• Management of HIT requires careful consideration of the balance between thrombotic risk and bleeding risk due to thrombocytopenia 5.