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 including flushes and coated catheters.

Key Steps in HIT Workup

• Laboratory testing includes an immunoassay (PF4/heparin ELISA) as an initial screen, followed by a functional assay (serotonin release assay or heparin-induced platelet activation) if the immunoassay is positive, as suggested by the ASH guideline panel 1.
• While awaiting results, start a non-heparin anticoagulant such as argatroban (initial 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.

Management Considerations

• Avoid platelet transfusions unless severe bleeding occurs, and monitor for thrombotic complications with appropriate imaging based on symptoms.
• Once platelet counts recover (typically >150,000/μL), transition to warfarin with overlap for at least 5 days and INR >2 for two consecutive days, as recommended by the American College of Chest Physicians evidence-based clinical practice guidelines 1.
• Continue anticoagulation for at least 3 months if HIT is confirmed, or longer if thrombosis occurred, to minimize the risk of recurrent thrombosis and improve patient outcomes 1.

Diagnosis and Treatment Phases

The diagnosis and management of HIT can be divided into several phases, including suspected HIT, acute HIT, subacute HIT A and B, and remote HIT, each with specific recommendations for testing and treatment, as outlined in the ASH 2018 guidelines 1. In patients with a high-probability 4T score and a positive immunoassay, the ASH guideline panel recommends continued avoidance of heparin and continued administration of a non-heparin anticoagulant at therapeutic intensity 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. Thrombocytopenia in patients receiving heparin has been reported at frequencies up to 30%. It can occur 2 to 20 days (average 5 to 9) following the onset of heparin therapy. Obtain platelet counts before and periodically during heparin therapy. Monitor thrombocytopenia of any degree closely

The workup for heparin-induced thrombocytopenia (HIT) involves:

• Discontinuing heparin therapy if the platelet count falls below 100,000/mm3 or if recurrent thrombosis develops
• Evaluating for HIT and HITT
• Administering an alternative anticoagulant if necessary
• Obtaining platelet counts before and periodically during heparin therapy to monitor for thrombocytopenia 2 Key steps in the workup include:
• Prompt discontinuation of heparin
• Evaluation for HIT and HITT
• Consideration of alternative anticoagulants Note that Argatroban is indicated for prophylaxis or treatment of thrombosis in adult patients with heparin-induced thrombocytopenia (HIT) 3

From the Research

Diagnosis of Heparin-Induced Thrombocytopenia (HIT)

• The diagnosis of HIT is based on the presence of clinical features, including a 50% fall in platelet count, appropriate timing of thrombocytopenia, development of new thrombosis despite thrombocytopenia and heparin therapy, and the absence of a more likely cause of thrombocytopenia 4.
• Documentation of an anti-PF4-heparin antibody is necessary, but is not sufficient to make the diagnosis since antibody formation occurs in a variety of clinical settings without the development of thrombocytopenia or thrombosis 4.
• Clinical scoring assessment using the 4Ts is used to maintain a high index of clinical suspicion, followed by appropriate stepwise laboratory testing to rule out HIT or establish the diagnosis 5.

Management of HIT

• All forms of heparin should be discontinued immediately when HIT is suspected or confirmed 4.
• An alternative form of anticoagulation should be administered until the platelet count recovers, with options including intravenous administration of argatroban, lepirudin, and bivalirudin, and subcutaneous administration of fondaparinux 4, 6.
• Warfarin therapy, if indicated, should be avoided until platelet recovery 4.
• Re-exposure to heparin can be avoided by use of alternative anticoagulants for most circumstances 4.

Treatment Options

• Argatroban has been shown to improve outcomes, particularly new thrombosis and death due to thrombosis, in patients with HIT 7.
• Fondaparinux has been successfully used in HIT, with complete platelet recovery observed in all cases in one study 6.
• The selection and use of nonheparin anticoagulation requires consideration of patient characteristics and institutional resources, with the goal of providing consistent, high-quality, and cost-effective care 8.