Detection and Significance of Heparin-Platelet Factor 4 Antibodies

Covalently linking heparin to antithrombin enhances prothrombinase inhibition on activated platelets

Factor (F)Xa within the prothrombinase complex is protected from inhibition by unfractionated heparin (UFH), enoxaparin and fondaparinux. We have developed a covalent antithrombin-heparin complex (ATH) with enhanced anticoagulant activity. We have also demonstrated that ATH is superior at inhibiting coagulation factors when assembled on artificial surfaces. The objective of the present study is to determine the ability of ATH vs AT+UFH to inhibit FXa within the prothrombinase complex when the enzyme complex is assembled on the more native platelet system. Discontinuous inhibition assays were performed to determine final k 2-values for inhibition of FXa, FXa within the platelet-prothrombinase, or FXa within prothrombinase devoid of various components. Thrombin generation and plasma clotting was also assayed in the presence of resting/activated platelets ± inhibitors. Protection of FXa was not observed for ATH, whereas a moderate 60% protection was observed for AT+UFH. ATH inhibited platelet-prothrombinase ∼4-fold faster than AT+UFH. Relative to intact prothrombinase, rates for FXa inhibition by AT+UFH in prothrombinase complexes devoid of either prothrombin (II)/activated platelets/FVa were higher. However, inhibition by AT+UFH of prothrombinase devoid of FII yielded slightly lower rates compared to free FXa inhibition. Thrombin generation and plasma clotting was enhanced with activated platelets, while inhibition was better by ATH compared to AT+UFH, thus suggesting an overall enhanced anticoagulant activity of ATH against platelet-bound prothrombinase complexes.

Heparin-induced thrombocytopenia in the pediatric population: a review of current literature

Heparin-induced thrombocytopenia is a rare and serious reaction to unfractionated heparin and low-molecular-weight heparins in children. Quick recognition, discontinuation of heparin, and subsequent treatment with an alternative anticoagulant are essential steps to prevent serious complications such as thrombus and limb amputation. The purpose of this review is to describe the clinical features of heparin-induced thrombocytopenia in children and to summarize the data available for its management. This paper summarizes data and relates the use of direct thrombin inhibitors with clinical outcomes. A literature search was conducted with Ovid, using the key terms argatroban, bivalirudin, hirulog, danaparoid, lepirudin, direct thrombin inhibitor, heparin-induced thrombocytopenia, thrombosis, warfarin, and fondaparinux. Articles were excluded if they were classified as editorials, review articles, or conference abstracts or if they involved patients 18 years of age or older or described disease states not related to thrombosis. Nineteen articles containing 33 case reports were identified and evaluated for this review. Of the 33 cases, 14, 10, 4, and 2 cases described the use of lepirudin, danaparoid, argatroban, and bivalirudin, respectively. Two cases did not report the type of anticoagulant used, and 1 case used aspirin. The most commonly reported complication was bleeding.

An Overview of Heparin-Induced Thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is an immune-mediated adverse drug reaction to heparin products leading to a prothrombotic state. Devastating clinical sequelae may result, including venous or arterial thromboembolism, limb amputation, and death. Heparin cessation alone is insufficient to manage HIT. Pharmacotherapy with argatroban or lepirudin is essential. This article reviews the pathogenesis, diagnosis, and pharmacotherapy of HIT.

Heparin-induced Thrombocytopenia: Pathophysiology, Diagnosis, and Review of Pharmacotherapy

Heparin-induced thrombocytopenia is an adverse drug reaction to heparin therapy leading to devastating clinical outcomes including venous thromboembolism, myocardial infarction, stroke, and limb amputation. Heparin cessation alone is not sufficient for the management of heparin-induced thrombocytopenia. Direct thrombin inhibitors, such as argatroban and lepirudin, are considered the mainstay for the management of heparin-induced thrombocytopenia. Case reports support the use of fondaparinux in the management of heparin-induced thrombocytopenia; however, randomized trials are still lacking. This article will review the pathophysiology, clinical presentation, complications, diagnosis, and pharmacotherapy management of heparin-induced thrombocytopenia.

Platelet transfusions in heparin-induced thrombocytopenia: a report of four cases and review of the literature

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is a complication of heparin therapy associated with thrombocytopenia and thrombosis. The diagnosis of HIT is based on clinical criteria and laboratory tests, including the serotonin release assay (SRA). Because HIT patients are thrombocytopenic, platelet (PLT) transfusions may be contemplated; however, many published reviews have concluded that PLT transfusions are contraindicated in HIT because they may precipitate thrombotic events. This study reports four patients with clinically suspected HIT who received PLT transfusions without complications, and the literature regarding this subject has been reviewed.

STUDY DESIGN AND METHODS

Patients with a SRA ordered for suspected HIT were retrospectively identified. Charts of patients with positive SRAs who received a PLT transfusion when HIT was clinically suspected were reviewed for evidence of PLT transfusion safety and efficacy. A comprehensive search of the published literature regarding PLT transfusions in patients with HIT was conducted.

RESULTS

A SRA was performed on 189 patients with suspected HIT. Thirteen patients tested positive and 4 of these received a PLT transfusion. No patient developed a thrombotic complication. All 4 patients had adequate posttransfusion PLT increments. Two of the 3 patients with active bleeding had cessation of bleeding after transfusion. Review of the literature revealed no case of a complication clearly attributable to PLT transfusion.

CONCLUSION

Four patients with clinically suspected HIT and a positive SRA were transfused PLTs both efficaciously and safely. These outcomes, combined with the results of the literature review, suggest that PLT transfusions should not be withheld when clinically indicated in patients with HIT.