History

Factors that increase the risk for heparin-induced thrombocytopenia (HIT) are as follows:

Use of unfractionated heparin (UFH) rather than low molecular weight heparin (LMWH)
Intravenous rather than subcutaneous administration of heparin
Longer duration of heparin use
Surgical (especially cardiac or orthopedic surgery) rather than medical patient
Female sex

Clinical features that help distinguish HIT from other forms of thrombocytopenia include the timing of onset and the presence of thrombosis (eg, venous thromboembolism) or other sequelae. In contrast to other drug-induced immune thrombocytopenia syndromes, HIT is generally not associated with bleeding.^[37]

Onset of HIT usually occurs 5-14 days after the start of heparin therapy. However, in patients with recent prior heparin exposure (within the past 100 days), persistence of circulating HIT antibodies may result in rapid-onset HIT, in which the platelet count falls within 24 hours of starting heparin.^[2]

Onset of HIT may also occur after heparin cessation. Delayed-onset HIT should be considered when a patient presents with thrombosis and unexplained thrombocytopenia up to 3 weeks after the end of heparin therapy.^[38]

Physical Examination

Patients with heparin-induced thrombocytopenia (HIT) may present with unusual characteristic sequelae, including the following:

Venous limb gangrene
Bilateral adrenal hemorrhagic infarction
Skin lesions at injection sites
Acute systemic reactions following an intravenous heparin bolus

Acute systemic reactions include chills, fever, dyspnea, chest pain, and flushing.^[39]Patients with HIT can also present with deep venous thrombosis (DVT) or pulmonary embolism. In patients with DVT who are started on warfarin, severe protein C depletion can develop, leading to warfarin-induced venous limb gangrene and likely loss of the limb.^[40]Less often, patients may present with arterial thromboembolism (eg, stroke, myocardial infarction).

Differential Diagnoses

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Media Gallery

Ultrasonographic image of a deep vein thrombosis (DVT).
Sequential images demonstrate treatment of iliofemoral deep venous thrombosis due to May-Thurner (Cockett) syndrome. Far left: View of the entire pelvis demonstrates iliac occlusion. Middle left: After 12 hours of catheter-directed thrombolysis, an obstruction at the left common iliac vein is evident. Middle right: After 24 hours of thrombolysis, a bandlike obstruction is seen; this is the impression made by the overlying right common iliac artery. Far left: After stent placement, image shows wide patency and rapid flow through the previously obstructed region. Note that the patient is in the prone position in all views. (Right and left are reversed.)
Ventilation-perfusion scan. Left image: Posterior view of normal findings on ventilation-perfusion scan. Right image: Posterior view of a perfusion scan that reveals a perfusion defect in the left upper quadrant. The defect in the middle of the image is due to the position of the heart.
Helical computed tomography scan of the pulmonary arteries. A filling defect in the right pulmonary artery is present, consistent with a pulmonary embolism.

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Sections Heparin-Induced Thrombocytopenia
Overview
Presentation
DDx
Workup
Treatment
Medication
Questions & Answers
Media Gallery
Tables
References

Feature	Score
Feature	2 points	1 point	0 points
Thrombocytopenia	>50% fall and platelet nadir 20-100 × 10⁹/L	30%-50% fall or platelet nadir 10-19× 10⁹/L	< 30% fall or platelet nadir < 10×10⁹/L
Timing of platelet count fall	Clear onset on day 5-10, or ≤1 d if heparin exposure within past 30 d	Consistent with day 5-10 fall, but not clear (eg, missing platelet counts); onset after day 10; or fall ≤1 day if heparin exposure 30-100 days ago	Platelet count fall ≤4 d without recent heparin exposure
Thrombosis or other sequelae	New thrombosis (confirmed); skin necrosis at heparin injection sites; anaphylactoid reaction after IV heparin bolus; adrenal hemorrhage	Progressive or recurrent thrombosis; erythematous skin lesions; thrombosis suspected but not proven	None
Other causes of thrombocytopenia	None apparent	Possible	Definite

Heparin-Induced Thrombocytopenia Clinical Presentation

History

Physical Examination

References

Tables

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