Profiling Heparin-Induced Thrombocytopenia (HIT) Antibodies in Hospitalized Patients With and Without Diabetes.

Heparin (H) anticoagulation in populations characterized by elevated platelet factor 4 (PF4) frequently elicits PF4/H antibodies, presenting a risk of heparin-induced thrombocytopenia. Recent studies have shown that anti-PF4/H enzyme-linked immunosorbent assays (ELISAs) detect antibodies in individuals never exposed to heparin. Platelet factor 4/H cross-reactive antibodies may result from PF4-mediated defense responses to injury or infection. This study questioned whether patients with diabetes are more likely to develop the endogenous cross-reactive antibodies. A comparison of healthy volunteers versus hospitalized patients with or without diabetes showed no significant differences in the prevalence of PF4/H ELISA-positive results. However, the group of patients who had both diabetes and an infectious condition had higher median antibody titer compared to other patients with or without diabetes regardless of reason for hospitalization. Higher PF4/H titers were also associated with patients with diabetes who were not on any medical therapy. In the future, determining whether PF4/H cross-reactive antibodies sensitize patients to respond adversely to heparin anticoagulation or predispose patients to other complications may be relevant to diabetes care.

Apixaban as an alternate oral anticoagulant for the management of patients with heparin-induced thrombocytopenia.

Due to the pronounced hypercoagulable state in heparin-induced thrombocytopenia (HIT), alternatives to heparin that do not interact with HIT antibodies are needed for anticoagulation management. This study was designed to determine whether the oral factor Xa inhibitor apixaban could be used. Functional platelet activation with apixaban in the presence of HIT antibodies was evaluated by the (14)C-serotonin release assay (SRA; washed platelets) and the heparin-induced platelet aggregation assay (PA-HIT; platelet-rich plasma). A consistent absence of platelet activation by apixaban (0.05-50 µg/mL) was observed: SRA (n = 35) 11 ± 4% and PA-HIT (n = 37) 8 ± 3% (mean ± standard error of the mean; positive is >20%) versus heparin (0.1 U/mL) 82 ± 3% SRA and 78 ± 6% PA-HIT (P < 0.01) versus enoxaparin (10 µg/mL) 73 ± 5% SRA and 62 ± 7% PA-HIT. Apixaban may provide an option for oral anticoagulation in patients with HIT, particularly for extended management and prevention.

Murine monoclonal antibody to platelet factor 4/heparin complexes as a potential reference standard for platelet activation assays in heparin-induced thrombocytopenia.

Quality control of the platelet activation assays to diagnose heparin-induced thrombocytopenia (HIT), (14)C-serotonin release assay (SRA) and platelet aggregation test (PAT) has yet to be established due to lack of reference standards and the difficulty of obtaining significant amounts of HIT antibodies from patients with HIT. We prepared a murine monoclonal antibody to human platelet factor 4 (hPF4)/heparin complexes (HIT-MoAb) and investigated the platelet activating action of HIT-MoAb by using SRA and PAT. The HIT-MoAb activated human platelets at low heparin concentration and the platelet activations were inhibited at high heparin concentration in both SRA and PAT. The HIT-MoAb produced a concentration-dependent effect. Moreover, the platelet activation at low heparin concentration was inhibited by anti-FcγRIIa antibody. These results indicated that HIT-MoAb has characteristics similar to human HIT antibodies regarding heparin-dependent platelet activation. Therefore, it is suggested that HIT-MoAb has the potential to be a positive control or reference standard in platelet activation assays.

Heparin-induced thrombocytopenia: an update.

Heparin-induced thrombocytopenia (HIT) is an immune response to heparin that can progress to severe thrombosis, amputation, and in some cases death. The diagnosis and treatment of HIT is complex, but needs to be considered in the clinical management of patients exposed to heparin due to its serious outcomes. Early diagnosis based on a comprehensive interpretation of clinical and laboratory information improves clinical outcomes. This begins with careful monitoring for thrombocytopenia and thrombosis during and for at least 5 to 10 days after heparin treatment of any dose and duration. Appropriate use and knowledgeable interpretation of laboratory tests for HIT are important, as these vary in sensitivity and specificity, with each type providing unique information. Clinical management of patients with HIT is with a non-heparin anticoagulant such as a direct thrombin inhibitor or danaparoid followed by a vitamin K antagonist for long-term treatment. Important drug-specific limitations, dosing, and monitoring guidelines must be respected for patient safety. There continues to be new developments in the field of HIT: laboratory testing, clinical scoring systems, and available new anticoagulants. Research and clinical studies will continue to address the unresolved issues and unmet clinical needs associated with HIT. This review summarizes the clinical management of HIT.

Clinical evaluation of acute systemic reaction and detection of IgG antibodies against PF4/heparin complexes in hemodialysis patients.

Heparin-induced thrombocytopenia (HIT) is a pathophysiological syndrome caused by platelet-activating antibodies that recognize PF4/heparin complexes. The abrupt onset of HIT following intravenous bolus heparin is known as an acute systemic reaction. Clinical features of this type of HIT may be similar to those of common complications during hemodialysis. The aim of the study was to identify whether the clinical features of the acute systemic reaction are caused by HIT or dialytic complications. Twenty-seven dialytic patients who had thrombocytopenia and clinical features of an acute systemic reaction were enrolled out of 202 HIT-suspected patients. Thirteen patients had HIT confirmed due to the presence of positive functional and immunoassays. Eight of the thirteen patients presented with acute systemic reactions due to HIT. The most common symptom of acute systemic reaction was dyspnea. The other nineteen patients, involving both HIT and non-HIT patients, had dialysis-complicated ASR. The major feature of the acute systemic reaction in hemodialysis was hypotension and its relevant symptoms. An immunoassay for the detection of IgG antibodies against PF4/heparin complexes (HIT-IgG) showed the wide-range linearity of the calibration curve by employing three concentrations of recombinant mouse monoclonal antibodies for PF4/heparin complexes. The results are expressed as micrograms of IgG in one milliliter. Significantly high levels in thirteen HIT patients were compared with levels in fourteen non-HIT patients. The highest median of 1,530 µg/ml (IQR: 3,267-813) was obtained in the presence of HIT associated with an acute systemic reaction. In HIT patients who did not show characteristics of an HIT-derived acute systemic reaction, the median was 339 µg/ml (1,178-834). Despite showing a positive ELISA, nine non-HIT patients without any platelet-activating antibodies showed a value of 97 µg/ml (166-56). The lowest median of 8.3 µg/ml (11-6) was in non-HIT patients with a negative ELISA. In conclusion, measurements of HIT-IgG -specific antibodies can facilitate an appropriate estimation in hemodialysis patients of whether the clinical features of an acute systemic reaction are caused by HIT or dialytic complications.

Simple scoring system for early management of heparin-induced thrombocytopenia.

This study was performed to develop a simple scoring system to aid in the early clinical management of patients suspected of heparin-induced thrombocytopenia (HIT) with regard to decisions for continued heparin therapy. The system was designed to arrive at low (0) or possible (1) probability scores without knowledge of laboratory test results (except platelet counts) to avoid delays. As the safest clinical approach is to discontinue heparin, intermediate and high scores were combined. Critically ill VA hospital patients (n = 100) with a ≥30% fall in platelet count were assessed by platelet aggregation (PA), (14)C-serotonin release assay ((14)C-SRA), and GTI ELISA. In this population, 53% were scored 1 and of these 43% were positive by laboratory test. Emphasizing the decision to discontinue heparin, the clinical signs of HIT were paramount for the immediate determination of a diagnosis of HIT without dependence on a positive laboratory test.

Laboratory methods and management of patients with heparin-induced thrombocytopenia.

The clinical effects of heparin are meritorious and heparin remains the anticoagulant of choice for most clinical needs. However, as with any drug, adverse effects exist. Heparin-induced thrombocytopenia (HIT) is an important adverse effect of heparin associated with amputation and death due to thrombosis. Although the diagnosis and treatment of HIT can be difficult and complex, it is critical that patients with HIT be identified as soon as possible to initiate early treatment to avoid thrombosis.

Low anticoagulant heparin targets multiple sites of inflammation, suppresses heparin-induced thrombocytopenia, and inhibits interaction of RAGE with its ligands.

While heparin has been used almost exclusively as a blood anticoagulant, important literature demonstrates that it also has broad anti-inflammatory activity. Herein, using low anti-coagulant 2-O,3-O-desulfated heparin (ODSH), we demonstrate that most of the anti-inflammatory pharmacology of heparin is unrelated to anticoagulant activity. ODSH has low affinity for anti-thrombin III, low anti-Xa, and anti-IIa anticoagulant activities and does not activate Hageman factor (factor XII). Unlike heparin, ODSH does not interact with heparin-platelet factor-4 antibodies present in patients with heparin-induced thrombocytopenia and even suppresses platelet activation in the presence of activating concentrations of heparin. Like heparin, ODSH inhibits complement activation, binding to the leukocyte adhesion molecule P-selectin, and the leukocyte cationic granular proteins azurocidin, human leukocyte elastase, and cathepsin G. In addition, ODSH and heparin disrupt Mac-1 (CD11b/CD18)-mediated leukocyte adhesion to the receptor for advanced glycation end products (RAGE) and inhibit ligation of RAGE by its many proinflammatory ligands, including the advanced glycation end-product carboxymethyl lysine-bovine serum albumin, the nuclear protein high mobility group box protein-1 (HMGB-1), and S100 calgranulins. In mice, ODSH is more effective than heparin in reducing selectin-mediated lung metastasis from melanoma and inhibits RAGE-mediated airway inflammation from intratracheal HMGB-1. In humans, 50% inhibitory concentrations of ODSH for these anti-inflammatory activities can be achieved in the blood without anticoagulation. These results demonstrate that the anticoagulant activity of heparin is distinct from its anti-inflammatory actions and indicate that 2-O and 3-O sulfate groups can be removed to reduce anticoagulant activity of heparin without impairing its anti-inflammatory pharmacology.

Profiling of heparin-induced thrombocytopenia antibody levels in patients with and without diabetes.

Heparin/platelet factor 4 (H:PF4) antibodies are the causative agent in heparin-induced thrombocytopenia (HIT). The antibodies are frequently formed after exposure to heparin, most commonly without any signs of clinical HIT. Heparin-induced thrombocytopenia antibodies have been detected by enzyme-linked immunosorbent assay (ELISA) in individuals who have not been exposed to heparin. It is possible that the antibodies could be elicited by PF4 associated with endogenous, heparin-like glycosaminoglycans (GAGs). This risk would be higher in individuals with endothelial dysfunction and chronic platelet activation. In the setting of an outpatient endocrinology clinic, both diabetic and nondiabetic patients were studied and compared with healthy volunteers. Heparin/platelet factor 4 antibody titers were measured by ELISA and analyzed to determine the frequency of clinically seropositive responses, and median and interquartile ranges of baseline antibody titers. The study found no increase in frequency of ELISA-positive patients among diabetic patients. Moreover, the diabetic population had lower overall level of H:PF4 antibody titer, especially the subgroups treated with thiazolidinedione drugs or angiotensin receptor blockers. Further studies are needed to determine whether subthreshold titers of HIT antibody may be reflective of the physiological state of platelet/endothelial balance.

Rivaroxaban--an oral, direct Factor Xa inhibitor--has potential for the management of patients with heparin-induced thrombocytopenia.

Rivaroxaban is an oral, direct activated Factor Xa (FXa) inhibitor in advanced clinical development for the prevention and treatment of thromboembolic disorders. Currently available anticoagulants include unfractionated heparin (UFH) and low molecular weight heparins (LMWHs); however, their use can be restricted by heparin-induced thrombocytopenia (HIT). HIT is usually caused by the production of antibodies to a complex of heparin and platelet factor-4 (PF4). This study was performed to evaluate, in vitro, the potential of rivaroxaban as an anticoagulant for the management of patients with HIT. UFH, the LMWH enoxaparin, fondaparinux and the direct thrombin inhibitor argatroban were tested to enable comparative analyses. Rivaroxaban did not cause platelet activation or aggregation in the presence of HIT antibodies, unlike UFH and enoxaparin, suggesting that rivaroxaban does not cross-react with HIT antibodies. Furthermore, rivaroxaban did not cause the release of PF4 from platelets and did not interact with PF4, unlike UFH and enoxaparin. These findings suggest that rivaroxaban may be a suitable anticoagulant for the management of patients with HIT.

Transition from argatroban to oral anticoagulation with phenprocoumon or acenocoumarol: effect on coagulation factor testing.

Treatment with the thrombin inhibitor argatroban is often followed by vitamin K-antagonist treatment. In this study, the behavior of coagulation factors measured under these treatment regimens is shown. Healthy subjects received infusions of 1.0, 2.0, or 3.0 microg/kg/hr argatroban before and during phenprocoumon or acenocoumarol dosing. Quantitation of factors II, VII, IX, and X by clot-based assays resulted in dose dependent, approximately 20%, lower than expected values in the presence of argatroban. On the contrary, values for the inhibitors, protein C and protein S, were higher. Cotherapy exaggerated the effect by vitamin K-antagonist alone. However, testing by immunologic and chromogenic assays did not show any effect by argatroban. Coupled with a lack of bleeding in the subjects, these data suggests that argatroban does not affect coagulation proteins and that the observations are only an assay artifact. Assay interferences must be considered when measuring coagulation proteins in patients receiving thrombin inhibitors.

The laboratory diagnosis and clinical management of patients with heparin-induced thrombocytopenia: an update.

Heparin-induced thrombocytopenia (HIT) is a serious adverse effect of heparin exposure that can progress to severe thrombosis, amputation, or death. HIT is an immune response in which antibodies cause platelet activation, platelet aggregation, the generation of procoagulant platelet microparticles, and activation of leukocytes and endothelial cells. Early diagnosis based on a comprehensive interpretation of clinical and laboratory information is important to improve clinical outcomes. However, limitations of the laboratory assays and atypical clinical presentations can make the diagnosis difficult. Clinical management of patients with HIT is with a non-heparin anticoagulant such as a direct thrombin inhibitor or danaparoid followed by a vitamin K antagonist for long-term treatment. The new anti-factor Xa drugs (fondaparinux, rivaroxaban, apixaban) and other non-heparin antithrombotic agents can potentially be used for the treatment of HIT if clinically validated. Important drug-specific limitations and dosing and monitoring guidelines must be respected for patient safety. Issues still exist regarding the optimal clinical management of HIT.

Inflammatory and hemostatic activation in patients undergoing off-pump coronary artery bypass grafting.

To characterize hemostatic differences imposed by 2 common cardiac surgeries, the authors studied patients undergoing coronary artery revascularization by off-pump (n = 13) or cardiopulmonary bypass on-pump (n = 26) technique. Blood samples collected to 4 days post-surgery were evaluated by flow cytometry and enzyme-linked immunosorbent assay. A significant inflammatory response occurred in both the groups after surgery shown by increased interleukin cytokines and C-reactive protein; however, levels peaked lower and hours later in the off-pump group. Platelets (P-selectin; platelet-leukocyte complexes) and leukocytes (CD11b) were activated only in on-pump patients. Thrombin generation was enhanced in both groups after surgery. Only in the on-pump patients, the thrombin-antithrombin complex, pro-thrombin fragment 1.2, and thrombomodulin (vascular integrity) decreased intraoperatively. Tissue plasminogen activator and plasminogen activator inhibitor-1 were greater in the on-pump patients. Off-pump surgery may place patients at higher risk of postoperative hypercoagulability because of normal platelet function, intraoperative thrombin generation, less fibrinolytic activity, and lack of vascular protection.

Unfractionated heparin compared with low-molecular-weight heparin as related to heparin-induced thrombocytopenia.

PURPOSE OF REVIEW: Heparin-induced thrombocytopenia is a severe side effect of treatment with unfractionated heparin. The relation of low-molecular-weight heparin to heparin-induced thrombocytopenia is less well understood. This review will summarize what is known about the similarities and differences between thrombocytopenia induced by low-molecular-weight heparin and that induced by unfractionated heparin. RECENT FINDINGS: The pathophysiology of unfractionated heparin-induced thrombocytopenia, caused by the development of antibodies to heparin/platelet factor 4 complexes, holds true for low-molecular-weight heparin because the molecules of the latter are of the same saccharidic structure as those of unfractionated heparin. Owing to their smaller size, however, low-molecular-weight heparin does not interact with platelet factor 4 and platelets as efficiently as does unfractionated heparin. This translates to a two- to threefold lower risk of immune sensitization (antibody generation and occurrence of clinical heparin-induced thrombocytopenia). Low-molecular-weight heparin-induced thrombocytopenia antibodies are more often immunoglobulin A and immunoglobulin M, in contrast to the immunoglobulin G antibodies generated with unfractionated heparin-induced thrombocytopenia, which tend to be more often associated with clinical heparin-induced thrombocytopenia. The clinical expression of low-molecular-weight heparin-induced thrombocytopenia is generally similar to that of unfractionated heparin-induced thrombocytopenia but can have a slower onset, more severe thrombocytopenia, and slower platelet count recovery. Given that low-molecular-weight heparin, of itself, is linked with heparin-induced thrombocytopenia pathophysiology and it can interact with most preexisting heparin-induced thrombocytopenia antibodies generated after exposure to unfractionated heparin, treatment of heparin-induced thrombocytopenia patients with low-molecular-weight heparin is contraindicated. SUMMARY: The risk of the development of heparin-induced thrombocytopenia with low-molecular-weight heparin treatment is reduced relative to the frequency of unfractionated heparin-induced thrombocytopenia, but it is not eliminated, and platelet counts should be monitored with treatment.