Thrombin generation and heparin‐induced thrombocytopenia

Abstract

Summary. Background: Heparin-induced thrombocytopenia (HIT) is a severe complication of heparin therapy. IgG antibodies targeting the platelet factor 4-heparin complex activate platelets and generate microparticles with procoagulant activity. Objectives: To determine whether the thrombin generation assay is capable of detecting procoagulant activity induced by patient platelet-poor plasma (PPP) in donor plateletrich plasma (PRP). Patients and methods: We explored two groups of patients; group 1 (n = 23): patients with a positive clinical and biological diagnosis of HIT; group 2 (n = 25): patients with a negative clinical and biological diagnosis of HIT. Mixtures of donor PRP and patient PPP (1:1) were incubated either with unfractionated heparin 0.2 U mL )1 or with physiological saline. Thrombin generation was assessed by calibrated thrombinography. The effect of heparin on the mixtures was evaluated according to the ratio of the values with and without heparin (wH/woH) of the five thrombogram parameters. Results: With low heparin concentrations, plasma of group 1 activates donor platelets and generates procoagulant activity. A set of three ratios outside the cut-off values corresponds to the ÔHIT thrombogram profileÕ, characterized by a highly specific aspect of the thrombogram wH in relation to the thrombogram woH. None of the group 2 patients presented a HIT thrombogram profile. The results of thrombinography correlate well with the results of the platelet aggregation test. Conclusion: Our studies illustrate the central paradox of HIT, namely enhancement of thrombin generation in the presence of heparin. The HIT thrombogram profile as it is defined in this study can detect the procoagulant activity of HIT IgG antibodies.

Pharmacology of Heparin and Related Drugs

“…When the large immune complexes form, the antibodies bound to the complexes can bind to the FcgIIa receptors on platelets, which crosslink platelets together (Kelton et al, 1988) and will cause platelet aggregation and activation. These two aspects give rise to the clearance of platelets (thrombocytopenia) and release of procoagulant elements that drive a thrombotic response (Hughes et al, 2000;Tardy-Poncet et al, 2009). HIT antibodies can also cause activation of endothelial cells (Cines et al, 1987), monocytes (Pouplard et al, 2001), and neutrophils (Xiao et al, 2008).…”

Platelet microparticle generation assay for heparin-induced thrombocytopenia diagnosis: How should we express the results?

“…Generation of platelet-derived microparticles (PMPs) occurs when platelets are activated by HIT sera. Moreover, PMPs serve as a catalytic surface for enhanced thrombin generation, considered as a major component of this adverse reaction [2,3]. The concentration of PMPs generated can be used as an endpoint in a functional assay [4].…”

Heparin‐induced thrombocytopenia: Current status and diagnostic challenges

“…There are a handful of other immuno-and functional assays, including fluid-phase EIAs, ATP-release chemiluminescence assays, flow cytometric detection of platelet microparticles, and thrombin generation studies that have been investigated in the research setting only, and like the above described flow cytometric studies, have yet to be validated prospectively in a clinical setting [11,[47][48][49][50]. The commercially available EIAs remain the most widely used Figure 3.…”

“…The resultant thrombocytopenia, however, is not associated with an increased bleeding risk. Instead, ongoing platelet activation by the immune complexes results in increased thrombin production and a systemic hypercoagulable state that can culminate in venous and/or arterial thrombosis [11].…”