What is the workup for Heparin-Induced Thrombocytopenia (HIT)?

From the Guidelines

The workup for Heparin-Induced Thrombocytopenia (HIT) should begin with clinical assessment using the 4T score, which evaluates thrombocytopenia timing, thrombosis, alternative causes, and platelet count drop, as recommended by the American Society of Hematology 2018 guidelines 1. For suspected HIT, immediately discontinue all heparin products and switch to a non-heparin anticoagulant such as argatroban (starting dose 0.5-1.2 mcg/kg/min adjusted to target aPTT 1.5-3 times baseline), bivalirudin (0.15-0.2 mg/kg/hr), or fondaparinux (weight-based dosing: 5-10 mg daily subcutaneously) 1. Laboratory testing should include both immunoassays (PF4/heparin ELISA) and functional assays (serotonin release assay), with the choice of assay influenced by diagnostic accuracy, availability, cost, feasibility, and turnaround time 1. The immunoassay is sensitive but less specific, while functional assays are more specific but less widely available 1. Platelet counts should be monitored daily until recovery, and even if thrombosis is not present, anticoagulation should continue for at least 30 days due to the high risk of thrombotic events 1. HIT occurs when heparin binds to platelet factor 4, forming complexes that trigger antibody production, leading to platelet activation, aggregation, and paradoxical thrombosis despite low platelet counts 1. Proper diagnosis and management are critical as mortality can reach 20% if untreated 1. Some studies suggest that direct oral anticoagulants (DOACs) may be a safe and effective alternative in select cases, but their use is not yet widely recommended 1. Key considerations in the management of HIT include:

• Discontinuation of heparin therapy
• Initiation of a non-heparin anticoagulant
• Monitoring of platelet counts and adjustment of anticoagulation therapy as needed
• Consideration of the use of DOACs in select cases, although this is not yet widely recommended. It is essential to follow the most recent guidelines and consult with a specialist if unsure about the management of HIT, as the condition can be life-threatening if not properly treated 1.

From the FDA Drug Label

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. HIT or HITT can occur up to several weeks after the discontinuation of heparin therapy Patients presenting with thrombocytopenia or thrombosis after discontinuation of heparin sodium should be evaluated for HIT or HITT.

The work up for Heparin-Induced Thrombocytopenia (HIT) includes:

• Discontinuation of heparin: if the platelet count falls below 100,000/mm3 or if recurrent thrombosis develops
• Evaluation for HIT and HITT: promptly evaluate patients for HIT and HITT if they present with thrombocytopenia or thrombosis after discontinuation of heparin sodium
• Administration of an alternative anticoagulant: if necessary, administer an alternative anticoagulant 2 2

From the Research

Heparin-Induced Thrombocytopenia (HIT) Workup

• HIT is a prothrombotic, immune-mediated adverse reaction to heparin therapy 3
• The condition is characterized by a moderate thrombocytopenia, with a median platelet count nadir of approximately 50 to 60 x 10(9) platelets/L 4
• Severe thrombocytopenia has been described in patients with HIT, and in these patients, antibody levels are high and severe clinical outcomes have been reported 4

Diagnosis of HIT

• The timing of the thrombocytopenia in relation to the initiation of heparin therapy is critically important, with the platelet count beginning to drop within 5 to 10 days of starting heparin 4
• A more rapid drop in the platelet count can occur in patients who have been recently exposed to heparin (within the preceding 3 months), due to preformed anti-heparin/PF4 antibodies 4
• The 4Ts clinical scoring assessment can be used to evaluate the likelihood of HIT 3

Management of HIT

• All heparin and heparin-containing products should be discontinued immediately 4, 3
• An alternative, non-heparin anticoagulant should be initiated, such as argatroban, lepirudin, bivalirudin, or danaparoid 4, 5
• Argatroban has been shown to be effective in reducing the risk of thromboembolic complications and improving outcomes in patients with HIT 6, 7, 5
• Warfarin therapy should not be initiated until the platelet count has recovered and the patient is systemically anticoagulated, and vitamin K should be administered to patients receiving warfarin at the time of diagnosis of HIT 4

Treatment Options for HIT

• Argatroban has been shown to be superior to other anticoagulant drugs, including lepirudin, desirudin, bivalirudin, and danaparoid, in terms of reducing hospitalization length, thromboembolic events, major and minor hemorrhagic events, and mortality rate 5
• The choice of alternative anticoagulant therapy should be individualized based on the patient's specific needs and clinical circumstances 3