Reducing the hospital burden of heparin-induced thrombocytopenia: impact of an avoid-heparin program

Nanopore-regulated in situ polymerization for synthesis of homogeneous heparan sulfate with low dispersity

The biological activities of heparan sulfate (HS) are intimately related to their molecular weights, degree and pattern of sulfation and homogeneity. The existing methods for synthesizing homogeneous sugar chains of low dispersity involve multiple steps and require stepwise isolation and purification processes. Here, we designed a mesoporous metal-organic capsule for the encapsulation of glycosyltransferase and obtained a microreactor capable of enzymatically catalyzing polymerization reactions to prepare homogeneous heparosan of low dispersity, the precursor of HS and heparin. Since the sugar chain extension occurs in the pores of the microreactor, low molecular weight heparosan can be synthesized through space-restricted catalysis. Moreover, the glycosylation co-product, uridine diphosphate (UDP), can be chelated with the exposed metal sites of the metal-organic capsule, which inhibits trans-cleavage to reduce the molecular weight dispersity. This microreactor offers the advantages of efficiency, reusability, and obviates the need for stepwise isolation and purification processes. Using the synthesized heparosan, we further successfully prepared homogeneous 6-O-sulfated HS of low dispersity with a molecular weight of approximately 6 kDa and a polydispersity index (PDI) of 1.032. Notably, the HS generated exhibited minimal anticoagulant activity, and its binding affinity to fibroblast growth factor 1 was comparable to that of low molecular weight heparins.

Anticoagulation stewardship: Improving adherence to clinical guidelines and reducing overuse of venous thromboembolism prophylaxis in hospitalized medical patients

Adherence to guideline recommendations for venous thromboembolism prophylaxis (VTE) in hospitalized medical patients is suboptimal despite national policies and institutional interventions. The aim of this quality improvement project was to improve adherence to guidelines and decrease the overuse of VTE prophylaxis in order to reduce the institutional cost for heparins. A multidisciplinary anticoagulation stewardship program (ACSP) using the audit and feedback strategy was implemented on the medicine inpatient units at a teaching hospital in Canada. The primary outcome measure was a comparison, pre and post introduction of the ACSP, of the costs per 6-month period for prophylactic dose enoxaparin and unfractionated heparin on the medicine units. The balancing measures were the 90-day VTE rate and major bleeding rate during the hospitalization. Six months after the implementation of the ACSP, the cost was decreased by >50 % without any observed negative impact on patient safety. This study demonstrates the potential for anticoagulation stewardship programs to optimize the use of VTE prophylaxis and reduce the associated costs and risks.

Improving Judicious Use of Heparin-Induced Thrombocytopenia Testing Through Electronic Health Record-Based Intervention

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is an immune-mediated drug reaction that can cause thromboembolism in the setting of thrombocytopenia. An enzyme-linked immunosorbent assay (ELISA)-based assay to screen for HIT antibodies (HAb) is available but has relatively low specificity and a correspondingly high false positive rate. The 4Ts score has been validated to determine the pretest probability of HIT. The authors hypothesized that an electronic health record (EHR)-based clinical decision support (CDS) tool incorporating the 4Ts score would reduce the volume of HAb orders.

METHODS

After implementing a CDS tool into the EHR, the researchers retrospectively evaluated the impact from November 2019 to October 2021, compared to a preintervention period (January to October 2019). The primary outcome was average tests per month. Secondary outcomes included rates of tests ordered per total inpatient encounters and proportion of HAb sent despite low 4Ts score in the postintervention study period.

RESULTS

Of 1,833 HAb sent during the study period, 1,217 occurred in the postintervention period. In the postintervention period compared with the preintervention period, the average orders per month was 50.5 (standard deviation [SD] 9.7) vs. 61.6 (SD 7.2) (p = 0.003), and the order incidence rate was 8.0 per 1,000 patient encounters postintervention vs. 9.2 per 1,000 patient encounters preintervention (rate ratio [RR] 0.87, 95% confidence interval [CI] 0.79-0.96, p = 0.002). Postintervention, 252 (20.7%) had a 4Ts score calculated as low probability, 759 (62.4%) as intermediate probability, and 131 (10.8%) as high probability, and 75 had no associated 4Ts score.

CONCLUSION

Implementation of a simple CDS tool reduced the rate of HAb orders, reducing unnecessary HAb testing.

Quality improvement approaches to heparin-induced thrombocytopenia: a scoping review

Background

Heparin-induced thrombocytopenia (HIT) is a relatively uncommon condition characterized by 2 exceedingly common phenomena in hospitalized patients: thrombocytopenia and heparin exposure. Consequently, HIT is frequently overdiagnosed and inappropriately treated. These issues are the focus of many quality improvement (QI) initiatives.

Objectives

In this scoping review, we identified and characterized all published QI studies on improving the diagnosis and management of HIT.

Methods

We conducted a systematic literature search through April 2022 for studies reporting on QI interventions regarding the diagnosis, treatment, and/or prevention of HIT.

Results

Thirty studies were included in the final review. Studies were separated into 5 groups based on the focus of the interventions: increasing HIT recognition, reducing HIT incidence, reducing HIT overdiagnosis, promoting safer HIT management, and creating HIT task forces. Nine studies focused on the implementation of 4Ts score calculator into electronic medical record orders for HIT testing, while only 1 evaluated the impact of reducing unfractionated heparin use in favor of low-molecular-weight heparin. Six studies focused on the implementation of direct thrombin inhibitor management protocols, while none evaluated the use of alternative anticoagulants in HIT management.

Conclusion

The bulk of published HIT QI research focused on reducing overdiagnosis and promoting safer direct thrombin inhibitor therapy, while minimal attention has been devoted to HIT prevention and the use of evidence-based alternative HIT therapies.

Heparin-induced thrombocytopenia associated with low-molecular-weight heparin: clinical feature analysis of cases and pharmacovigilance assessment of the FAERS database

Background: Unfractionated heparin (UFH) and low-molecular-weight heparin (LMWH) are commonly used anticoagulants for the management of arterial and venous thromboses. However, it is crucial to be aware that LMWH can, in rare cases, lead to a dangerous complication known as heparin-induced thrombocytopenia (HIT). The objective of this study was to evaluate the pharmacovigilance and clinical features of HIT associated with LMWH, as well as identify treatment strategies and risk factors to facilitate prompt management. Methods: We extracted adverse event report data from the FDA Adverse Event Reporting System (FAERS) database for pharmacovigilance assessment. Case reports on LMWH-induced thrombocytopenia dated up to 20 March 2023 were collected for retrospective analysis. Results: Significantly elevated reporting rates of HIT were shown in adverse event (AE) data of LMWHs in the FAERS database, while tinzaparin had a higher proportional reporting ratio (PRR) and reporting odds ratio (ROR) than other LMWHs, indicating a greater likelihood of HIT. Case report analysis indicated that a total of 43 patients showed evidence of LMWH-induced thrombocytopenia with a median onset time of 8 days. Almost half of the events were caused by enoxaparin. LMWHs were mainly prescribed for the treatment of embolism and thromboprophylaxis of joint operation. Patients with a history of diabetes or surgery appeared to be more susceptible to HIT. Clinical symptoms were mostly presented as thrombus, skin lesion, and dyspnea. Almost 90% of the patients experienced a platelet reduction of more than 50% and had a Warkentin 4T score of more than 6, indicating a high likelihood of HIT. In all patients, LMWHs that were determined to be the cause were promptly withdrawn. Following the discontinuation of LMWHs, almost all patients were given alternative anticoagulants and eventually achieved recovery. Conclusion: LMWH-induced thrombocytopenia is rare but serious, with increased risk in patients with diabetes or a surgical history. Prompt recognition and management are crucial for the safe use of LMWHs.

Prevalence and outcomes of heparin-induced thrombocytopenia in hospitalized patients with venous thromboembolic disease: Insight from national inpatient sample

OBJECTIVE

The mainstay of therapy for patients with venous thromboembolic disease (VTE) is anticoagulation. In the inpatient setting, majority of these patients are treated with heparin or low molecular weight heparin. The prevalence and outcomes of heparin-induced thrombocytopenia (HIT) in hospitalized patients with venous thromboembolic disease (VTE) is unknown.

METHODS

This nationwide study identified patients with VTE from the National Inpatient Sample database between January 2009 and December 2013. Among these patients, we compared in-hospital outcomes of patients with and without HIT using a propensity score-matching algorithm. The primary outcome was in-hospital mortality. Secondary outcomes included rates of blood transfusions, intracranial hemorrhage, gastrointestinal bleed, length of hospital stay, and total hospital charges.

RESULTS

Among 791,932 hospitalized patients with VTE, 4948 patients (0.6%) were noted to have HIT (mean age, 62.9 ±16.2 years; 50.1% female). Propensity-matched comparison showed higher rates of in-hospital mortality (11.01% vs 8.97%; P < .001) and blood transfusions (27.20% vs 20.23%; P < .001) in patients with HIT compared with those without HIT. No significant differences were noted in intracranial hemorrhage rates (0.71% vs 0.51%; P > .05), gastrointestinal bleed (2.00% vs 2.22%; P > .05), length of hospital stay (median, 6.0 days; interquartile range [IQR], 3.0-11.0 vs median, 6.0 days; IQR, 3.0-10.0 days; P > .05), and total hospital charges (median, $36,325; IQR, $17,798-$80,907 vs median, $34,808; IQR, $17,654-$75,624; P > .05).

CONCLUSIONS

This nationwide observational study showed that 0.6% of hospitalized patients with VTE in the United States have HIT. The presence of HIT was associated with higher in-hospital mortality and blood transfusion rates compared with those without HIT.

Heparin-induced thrombocytopenia: An illustrated review

Heparin-induced thrombocytopenia (HIT) is an immune-mediated adverse drug effect from unfractionated or low-molecular-weight heparin that results in thrombocytopenia and potentially catastrophic thrombosis. HIT occurs due to the development of platelet-activating antibodies against multimolecular complexes of platelet factor 4 and heparin. Given the frequency of thrombocytopenia and heparin use among hospitalized patients, calculation of the 4Ts Score is recommended to identify patients at increased likelihood of HIT and direct further evaluation. In patients with an intermediate or high probability 4Ts Score, an immunoassay and functional assay are recommended to confirm or refute the diagnosis of HIT. Heparin avoidance and initiation of nonheparin anticoagulation are the mainstays of acute HIT management. In this illustrated review, we provide visual summaries of the diagnosis and management of HIT, highlighting connections between pathophysiology and clinical care as well as summarizing efforts in quality improvement in the field. We further emphasize common pitfalls and pearls in diagnosis and management to encourage evidence-based care. We include graphical representation of the unique challenges of HIT with cardiopulmonary bypass and also delineate autoimmune HIT and its subtypes.

Evaluating the immunogenicity of heparin and heparin derivatives by measuring their binding to platelet factor 4 using biolayer interferometry

Heparin (HP) is a polysaccharide that is widely used in the clinic as an anticoagulant. A major side effect associated with HP is the heparin-induced thrombocytopenia (HIT), which is initiated by the immune response to complex formed by HP and platelet factor 4 (PF4). Low molecular weight heparins (LMWHs) are the depolymerized version of HP, which have reduced risks of inducing HIT. However, it is still necessary to evaluate the immunogenicity of LMWHs to ensure their drug safety. Since HIT involves very complicated processes, the evaluation of HP and LMWH immunogenicity requires experiments from multiple aspects, of which the binding affinity between HP and PF4 is a key property to be monitored. Herein, we developed a novel competitive biolayer interferometry (BLI) method to investigate the binding affinity between HP and PF4. The influence of different domains in HP on its immunogenicity was compared for better understanding of the molecular mechanism of HP immunogenicity. Furthermore, the half maximal inhibitory concentration (IC50) of HP and LMWH can be measured by competitive combination, which is important for the quality control during the developing and manufacturing of HP and LMWH drugs.

Heparin-induced Thrombocytopenia: Perioperative Diagnosis and Management

Heparin-induced thrombocytopenia is a severe prothrombotic disease. Timely diagnosis and treatment are essential. Application of diagnostic algorithms based on validated clinical scoring tools and rapid, specific laboratory assays may improve outcomes.

Thrombocytopenia Due to Direct Oral Anticoagulation and Low-Molecular-Weight Heparin

Direct oral anticoagulants (DOACs) are becoming increasingly prevalent in the general population for anticoagulation. However, rare adverse effects from these medications are still being discovered. Thrombocytopenia has previously been reported with these medications, but its clinical significance is still unknown. We present a patient who developed thrombocytopenia from apixaban and who subsequently developed a severe presentation of heparin-induced thrombocytopenia (HIT) from enoxaparin. This raises the possibility that thrombocytopenia from oral anticoagulants increases the likelihood of the development of heparin-induced thrombocytopenia.

Cost reduction associated with heparin-induced thrombocytopenia panel ordering for enoxaparin versus heparin for prophylactic and therapeutic use: A retrospective analysis in a community hospital setting

Background:

Most hospitals still use unfractionated heparin (UFH) as the primary agent for venous thromboembolism (VTE) prophylaxis in the hospital setting due to ease of use and insignificant cost. However, the risk of heparin-induced thrombocytopenia (HIT) has led some groups to favor other options for therapeutic and prophylactic anticoagulation. This is particularly relevant in light of recent data demonstrating a lower rate of HIT in patients receiving enoxaparin compared with UFH. This study examines the cost-effectiveness of enoxaparin, compared to UFH for prophylactic and therapeutic usage in hospitals.

Methods:

We conducted a retrospective chart review of patients who underwent HIT panel testing at the Inspira Health Network, Vineland campus (an approximately 262-bedded community hospital located in southern New Jersey that services a population of approximately 61,050) from the period of April 1, 2015 through December 31, 2016. The starting date represents the time from which enoxaparin became the primary alternative anticoagulant available at this hospital. Records of the total usage and cost of UFH and enoxaparin for the specified time period were collected from the hospital pharmacy database for evaluation, as were records of HIT panels. The information was analyzed to determine the frequency of HIT panel testing orders for patients receiving UFH versus those receiving enoxaparin. Annual cost-savings for the hospital were extrapolated using the comparative incidence of HIT panels and associated costs, including increased length of stay, hematology/oncology consultation, use of an alternative anticoagulant, critical bleeding requiring transfusion, and complications of HIT-associated thrombosis. These variables were multiplied by the incidence rate for each specified drug and usage to determine the daily cost for each drug.

Results:

The use of enoxaparin did not result in a significant decrease in the ordering of HIT panels in the hospital, with a relative rate ratio of 0.948 (95% confidence interval: 0.336, 2.21). When the data were stratified to examine prophylactic and therapeutic anticoagulation, there was a marked difference in the frequency of HIT testing. The rate ratio of HIT panel orders for patients receiving therapeutic enoxaparin rather than intravenous (IV) UFH was 0.118 (0.006, 0.625). These numbers were used to extrapolate the total daily cost of enoxaparin compared with IV UFH; therapeutic enoxaparin cost $30.66, while IV UFH cost $162.30. IV UFH use was associated with a higher incidence rate of HIT panel orders, and consequently a higher daily cost due to the likelihood of increased length of stay, use of alternative anticoagulation, bleeding requiring transfusion, and request for expert consultation.

Conclusion:

In this study, the use of enoxaparin was associated with a significant cost-saving over IV UFH when used for therapeutic anticoagulation, but this cost saving was not observed for prophylactic anticoagulation.

Quantitative and Qualitative Platelet Derangements in Cardiac Surgery and Extracorporeal Life Support

Thrombocytopenia and impaired platelet function are known as intrinsic drawbacks of cardiac surgery and extracorporeal life supports (ECLS). A number of different factors influence platelet count and function including the inflammatory response to a cardiopulmonary bypass (CPB) or to ECLS, hemodilution, hypothermia, mechanical damage and preoperative treatment with platelet-inhibiting agents. Moreover, although underestimated, heparin-induced thrombocytopenia is still a hiccup in the perioperative management of cardiac surgical and, above all, ECLS patients. Moreover, recent investigations have highlighted how platelet disorders also affect patients undergoing biological prosthesis implantation. Though many hypotheses have been suggested, the mechanism underlying thrombocytopenia and platelet disorders is still to be cleared. This narrative review aims to offer clinicians a summary of their major causes in the cardiac surgery setting.

Pathogenesis of heparin-induced thrombocytopenia

There are currently no effective substitutes for high intensity therapy with unfractionated heparin (UFH) for cardiovascular procedures based on its rapid onset of action, ease of monitoring and reversibility. The continued use of UFH in these and other settings requires vigilance for its most serious nonhemorrhagic complication, heparin induced thrombocytopenia (HIT). HIT is an immune prothrombotic disorder caused by antibodies that recognize complexes between platelet factor 4 (PF4) and polyanions such as heparin (H).The pathogenicity of anti-PF4/H antibodies is likely due to the formation of immune complexes that initiate intense procoagulant responses by vascular and hematopoietic cells that lead to the generation of platelet microparticles, monocyte and endothelial cell procoagulant activity, and neutrophil extracellular traps, among other outcomes. The development of anti-PF4/H antibodies after exposure to UFH greatly exceeds the incidence of clinical disease, but the biochemical features that distinguish pathogenic from nonpathogenic antibodies have not been identified. Diagnosis relies on pretest clinical probability, screening for anti-PF4/H antibodies and documentation of their platelet activating capacity. However, both clinical algorithms and test modalities have limited predictive values making diagnosis and management challenging. Given the unacceptable rates of recurrent thromboembolism and bleeding associated with current therapies, there is an unmet need for novel rational nonanticoagulant therapeutics based on the pathogenesis of HIT. We will review recent developments in our understanding of the pathogenesis of HIT and its implications for future approaches to diagnosis and management.

Systems-based hematology: highlighting successes and next steps

Systems-based hematology is dedicated to improving care delivery for patients with blood disorders. First defined by the American Society of Hematology in 2015, the idea of a systems-based hematologist arose from evolving pressures in the health care system and increasing recognition of opportunities to optimize the quality and cost effectiveness of hematologic care. In this review, we begin with a proposed framework to formalize the discussion of the range of initiatives within systems-based hematology. Classification by 2 criteria, project scope and method of intervention, facilitates comparison between initiatives and supports dialogue for future efforts. Next, we present published examples of successful systems-based initiatives in the field of hematology, including efforts to improve stewardship in the diagnosis and management of complex hematologic disorders (eg, heparin-induced thrombocytopenia and thrombophilias), the development of programs to promote appropriate use of hematologic therapies (eg, blood products, inferior vena cava filters, and anticoagulation), changes in care delivery infrastructure to improve access to hematologic expertise (eg, electronic consultation and disorder-specific care pathways), and others. The range of projects illustrates the broad potential for interventions and highlights different metrics used to quantify improvements in care delivery. We conclude with a discussion about future directions for the field of systems-based hematology, including extension to malignant disorders and the need to define, expand, and support career pathways.

Impact of a Clinical Decision-Support Tool on Venous Thromboembolism Prophylaxis in Acutely Ill Medical Patients

Background: Adherence to guideline-based venous thromboembolism (VTE) prophylaxis recommendations is often inadequate. Effective improvement strategies are needed. Objective: The purpose of this quality improvement initiative was to increase use of the facility's preferred pharmacologic VTE prophylaxis, reduce unnecessary VTE prophylaxis use, and reduce use of pharmacologic VTE prophylaxis in high bleeding risk patients, in accordance with guideline-based recommendations. Methods: Clinical pharmacists spearheaded the development and implementation of a clinical decision-support tool (CDST) integrated within a Veterans Health Administration electronic health record (EHR). The CDST focused on VTE prophylaxis in acutely ill medical patients and guided prescribers to guideline-based recommendations. Following review and approval, the CDST underwent activation in the EHR. A subsequent intervention occurred, year 2 post-intervention, which embedded this CDST into the EHR admission process and admission menus. A drug message was added in the EHR to alert prescribers that low-molecular-weight heparin was the preferred agent. Measures were evaluated pre-intervention, year 1 post-intervention, and year 2 post-intervention. Results: After intervention, there were statistically significant increases in the proportion of patients receiving the facility's preferred pharmacologic VTE prophylaxis agent, enoxaparin, and a statistically significant decrease in the proportion of unwarranted VTE prophylaxis. The proportion of inappropriate pharmacologic VTE prophylaxis in high bleeding risk patients decreased, but this result did not reach statistical significance. Conclusion: The improvements observed suggest the beneficial role of CDSTs integrated into the EHR to increase adherence to guideline-based VTE prophylaxis recommendations.

Safety and Efficacy of High-Dose Unfractionated Heparin Versus High-Dose Enoxaparin for Venous Thromboembolism Prevention in Morbidly Obese Hospitalized Patients

BACKGROUND

Venous thromboembolism is a cause of morbidity and mortality in hospitalized patients, and morbid obesity increases this risk. Various prophylaxis dosing strategies have been investigated. However, it is unclear if high-fixed dose enoxaparin or high-fixed dose unfractionated heparin thromboprophylaxis is optimal for minimizing the incidence of major bleeding and reducing hospital-acquired venous thromboembolism.

METHODS

A single-center retrospective observational study was conducted in hospitalized patients who were morbidly obese (body mass index ≥40 kg/m²) and who received either high-fixed dose enoxaparin (40 mg every 12 hours) or unfractionated heparin (7500 units every 8 hours) for venous thromboembolism prophylaxis. Co-primary outcomes included incidence of major bleeding and venous thromboembolism diagnosed during hospitalization. Predictors of major bleeding were evaluated by multivariable regression.

RESULTS

In the 305 patients included (n = 190 unfractionated heparin, n = 115 enoxaparin), the incidence of major bleeding was significantly higher in the unfractionated heparin group (odds ratio [OR] 1.85, 95% confidence interval [CI] 1.07-3.13; P = 0.025), with no significant difference in the incidence of venous thromboembolism diagnosed during hospitalization. The only independent predictors of major bleeding were intensive care acuity (OR 3.32, 95% CI 1.91-5.78; P <0.001) and selection of unfractionated heparin rather than enoxaparin for venous thromboembolism prophylaxis (OR 2.16, 95% CI 1.22-3.82; P = 0.008).

CONCLUSION

High-fixed dose unfractionated heparin for venous thromboembolism prophylaxis may lead to a higher risk of major bleeding events compared with high-fixed dose enoxaparin in patients who are morbidly obese.

Heparin-induced thrombocytopenia (HIT): Review of incidence, diagnosis, and management

Heparin-induced thrombocytopenia (HIT) is a life and limb-threatening complication of heparin exposure. Here, we review the pathogenesis, incidence, diagnosis, and management of HIT. The first step in thwarting devastating complications from this entity is to maintain a high index of clinical suspicion, followed by an accurate clinical scoring assessment using the 4Ts. Next, appropriate stepwise laboratory testing must be undertaken in order to rule out HIT or establish the diagnosis. In the interim, all heparin must be stopped immediately, and the patient administered alternative anticoagulation. Here we review alternative anticoagulation choice, therapy alternatives in the difficult-to-manage patient with HIT, and the problem of overdiagnosis.

Clinical and economic burden of heparin-induced thrombocytopenia in hospitalized patients undergoing percutaneous peripheral arterial interventions

Background

Percutaneous peripheral arterial intervention (PPAI) patients are at a high risk of developing heparin-induced thrombocytopenia due to the need for repeated and prolonged heparin exposure. We sought to investigate the incidence, outcomes, and economic impact of heparin-induced thrombocytopenia post-PPAI utilizing the National Inpatient Sample.

Methods

All patients who underwent PPAI (age ≥18 years) from 2007 to 2014 were identified by using ICD-9-CM codes. Patients were then classified into two groups based on the presence or absence of heparin-induced thrombocytopenia during hospitalization. In-hospital outcomes were compared between the two groups after propensity-score matching to account for differences in baseline characteristics.

Results

Heparin-induced thrombocytopenia was reported in 527 patients (0.23%). After adjusting for patient-level and hospital-level characteristics, in-hospital mortality differences were not significantly different between patients with heparin-induced thrombocytopenia vs. those without heparin-induced thrombocytopenia (odds ratio (OR) 1.02, 95% confidence interval (CI) 0.67 to 1.57, p = 0.951). However, PPAI patients with heparin-induced thrombocytopenia were more likely to develop ischemic stroke (OR 3.84, 95%CI 1.26 to 11.75, p = 0.018), deep venous thrombosis/pulmonary embolism (OR 1.32, 95%CI 0.79 to 1.79, p = 0.078), and acute kidney injury requiring dialysis (OR 4.04, 95%CI 1.72 to 9.50, p = 0.001). Furthermore, post-PPAI patients who developed heparin-induced thrombocytopenia had longer hospitalizations (13.8 vs. 9.8 days, p < 0.0001), higher cost of stay ($62,022 vs. $44,904, p < 0.0001), and higher rates of non-routine home discharges (50.15% vs. 42.19%, p = 0.013).

Conclusion

Among patients who underwent PPAI, heparin-induced thrombocytopenia was associated with a higher risk of venous thrombosis/pulmonary embolism, ischemic stroke, acute kidney injury requiring dialysis, prolonged hospital stay, and increased cost.

Evaluation of unmet clinical needs in prophylaxis and treatment of venous thromboembolism in high-risk patient groups: cancer and critically ill

Background

Clinical practice shows that venous thromboembolism (VTE) presents a substantial burden in medical patients, and awareness and advocacy for its primary and secondary prevention remains inadequate. Specific patient populations, such as those with cancer and the critically ill, show elevated risk for VTE, bleeding or both, and significant gaps in VTE prophylaxis and treatment exist in these groups.

Objective

To present novel insights and consolidated evidence collected from experts, clinical practice guidelines and original studies on the unmet needs in thromboprophylaxis, and on the treatment of VTE in two high-risk patient groups: patients with cancer and the critically ill.

Methodology

To identify specific unmet needs in the management of VTE, a methodology was designed and implemented that assessed gaps in prophylaxis and treatment of VTE through interviews with 44 experts in the field of thrombosis and haemostasis, and through a review of current guidelines and seminal studies to substantiate the insights provided by the experts. The research findings were then analysed, discussed and consolidated by a multidisciplinary group of experts.

Results

The gap analysis methodology identified shortcomings in the VTE risk assessment tools, patient stratification approaches for prophylaxis, and the suboptimal use of anticoagulants for primary prophylaxis and treatment.

Conclusions

Specifically, patients with cancer need better VTE risk assessment tools to tailor primary thromboprophylaxis to tumour types and disease stages, and the potential for drug–drug interactions needs to be considered. In critically ill patients, unfractionated heparin is not advised as a first-line treatment option, and the strength of evidence is increasing for direct oral anticoagulants as a treatment option over low-molecular-weight heparins.

Electronic supplementary material

The online version of this article (10.1186/s12959-019-0196-6) contains supplementary material, which is available to authorized users.

Drug-associated thrombocytopenia

Many drugs have been implicated in drug-induced immune thrombocytopenia (DITP). Patients with DITP develop a drop in platelet count 5 to 10 days after drug administration with an increased risk of hemorrhage. The diagnosis of DITP is often challenging, because most hospitalized patients are taking multiple medications and have comorbidities that can also cause thrombocytopenia. Specialized laboratory diagnostic tests have been developed and are helpful to confirm the diagnosis. Treatment of DITP involves discontinuation of the offending drug. The platelet count usually starts to recover after 4 or 5 half-lives of the responsible drug or drug metabolite. High doses of intravenous immunoglobulin can be given to patients with severe thrombocytopenia and bleeding. Although in most cases, DITP is associated with bleeding, life-threatening thromboembolic complications are common in patients with heparin-induced thrombocytopenia (HIT). Binding of antiplatelet factor 4/heparin antibodies to Fc receptors on platelets and monocytes causes intravascular cellular activation, leading to an intensely prothrombotic state in HIT. The clinical symptoms include a decrease in platelet counts by >50% and/or new thromboembolic complications. Two approaches can help to confirm or rule out HIT: assessment of the clinical presentation using scoring systems and in vitro demonstration of antiplatelet factor 4/heparin antibodies. The cornerstone of HIT management is immediate discontinuation of heparin when the disease is suspected and anticoagulation using nonheparin anticoagulant. In this review, we will provide an update on the pathophysiology, diagnosis, and management of both DITP and HIT.

Antithrombotic therapy management of adult and pediatric cardiac surgery patients

Despite the development of catheter-based interventions for ischemic and valvular heart disease, hundreds of thousands of people undergo open heart surgery annually for coronary artery bypass graft (CABG), valve replacement or cardiac assist device implantation. Cardiac surgery patients are unique because therapeutic anticoagulation is required during cardiopulmonary bypass. Developmental hemostasis and altered drug metabolism affect management in children. This narrative review summarizes the current evidence-based and consensus guidelines regarding perioperative, intraoperative and postoperative antithrombotic therapy in patients undergoing cardiac surgery. Anticoagulation preoperatively is required in the setting of cardiac arrhythmias, prior valve replacement or history of venous thromboembolism. In patients with ischemic heart disease, aspirin is continued in the perioperative period, whereas oral P2Y12 antagonists are withheld for 5-7 days to reduce the risk of perioperative bleeding. Intraoperative management of cardiopulmonary bypass in adults and children includes anticoagulation with unfractionated heparin. Variability in dose-response to heparin and influence of other medical conditions on dosing and reversal of heparin make intraoperative anticoagulation challenging. Vitamin K antagonist therapy is the standard anticoagulant after mechanical heart valve or left ventricular assist device (LVAD) implantation. Longer duration of dual antiplatelet therapy is recommended after CABG if patients undergo surgery because of acute coronary syndrome. Antiplatelet therapy after LVAD implantation includes aspirin, dipyridamole and/or clopidogrel in children and aspirin in adults. A coordinated approach between hematology, cardiology, anesthesiology, critical care and cardiothoracic surgery can assist to balance the risk of thrombosis and bleeding in patients undergoing cardiac surgery.

Disease burden, complication rates, and health-care costs of heparin-induced thrombocytopenia in the USA: a population-based study

BACKGROUND

Heparin-induced thrombocytopenia can be a life-threatening and limb-threatening complication of heparin therapy. Incidence and complication rates of this condition have been extrapolated from studies with modest sample sizes, and despite the availability of therapeutic interventions the outcomes of heparin-induced thrombocytopenia are not well understood. We aimed to estimate disease burden, complication rates, and costs of heparin-induced thrombocytopenia in the USA.

METHODS

In this population-based study we analysed data from 2009 to 2013 from the Nationwide (National) Inpatient Sample (NIS), a large, all-payer inpatient health-care database in the USA. To validate the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) code for heparin-induced thrombocytopenia (289.84), we defined the sensitivity and specificity of this code using patient data from 2013 from a local hospital (Froedtert Memorial Lutheran Hospital, Milwaukee, WI, USA). The primary outcomes assessed were the incidence of hospital discharges with codes for heparin-induced thrombocytopenia and of discharges for heparin-induced thrombocytopenia associated with cardiopulmonary bypass, haemodialysis, hip or knee arthroplasty, trauma or injury (or both), and gingival or periodontal disease (or both). We also assessed the incidence of thrombosis, bleeding, limb or digit amputation, mortality, length of hospital stay, and associated hospital charges.

FINDINGS

Between 2009 and 2013, 97 566 discharges from the NIS assigned the ICD-9-CM code for heparin-induced thrombocytopenia, and 149 911 247 discharges coded for non-heparin-induced thrombocytopenia, were analysed. Overall, heparin-induced thrombocytopenia was identified in 97 566 (0·065%; SE 0·0012) of 150 008 813 discharges, corresponding to approximately one in 1500 hospital admissions. Patients undergoing cardiopulmonary bypass had the highest rates of heparin-induced thrombocytopenia (7702 [0·63%; SE 0·03] of 1 230 362), followed by those undergoing haemodialysis (23 012 [0·47%; 0·01] of 4 908 100), those with gingival or periodontal disease, or both (106 [0·12%; 0·03] of 88 621), and those with trauma or injury, or both (541 [0·09%; 0·01] of 602 944); patients with hip (845 [0·04%; 0·004] of 1 943 353) and knee (676 [0·02%; 0·002] of 3 022 602) arthroplasty had the lowest rates of heparin-induced thrombocytopenia. Thrombosis (29 079 [29·8%; SE 0·4] of 97 566) and bleeding (6044 [6·2%; 0·2] of 97 566) were common complications in heparin-induced thrombocytopenia, and 1446 (23·9%; 1·2) of 6044 patients with heparin-induced thrombocytopenia who had haemorrhage died. 742 (0·76%; SE 0·06) of 97 566 patients with heparin-induced thrombocytopenia discharges underwent amputations compared with 173 043 (0·12%; 0·001) of 149 911 247 with non-heparin-induced thrombocytopenia discharges (adjusted odds ratio 5·095 [95% CI 4·309-6·023]; p<0·0001). Overall, in-hospital mortality was 9842 (10·1%; SE 0·2) of 97 508 in discharge summaries coded for heparin-induced thrombocytopenia compared with 3 206 700 (2·1%; 0·01) of 149 811 891 in discharges for non-heparin-induced thrombocytopenia (adjusted odds ratio 4·075 [95% CI 3·846-4·317]; p<0·0001). The median length of stay among live discharges was 8·9 days (IQR 4·6-17·1) and total hospital charges were US$83 072 (IQR 37 240-188 419) for heparin-induced thrombocytopenia discharges compared with 2·6 days (1·4-4·8) and $21 360 (11 426-41 917) for non-heparin-induced thrombocytopenia discharges (p<0·0001 for both). 333 discharges from a local hospital were analysed to assess the diagnostic sensitivity and specificity of the heparin-induced thrombocytopenia ICD-9-CM code; sensitivity was 90·9% (95% CI 57·1-99·5) and specificity was 94·4% (91·1-96·6).

INTERPRETATION

Complication rates for heparin-induced thrombocytopenia remain high and more effective preventive and treatment interventions are needed.

FUNDING

None.

Recent advances in understanding and management of acquired thrombocytopenia

There are numerous congenital and acquired causes of thrombocytopenia. Thrombocytopenia could be a result of decreased bone marrow production, increased consumption, increased destruction, splenic sequestration or a combination of these causes. In this review, we have focused on some of the serious acquired causes of thrombocytopenia. There have been some significant advances in our understanding of the pathophysiology, diagnostic testing, and treatment of immune thrombocytopenia, heparin-induced thrombocytopenia, thrombotic thrombocytopenic purpura, and atypical hemolytic uremic syndrome over the past five years. These advances have resulted in a significant decrease in mortality and morbidity of patients with these disorders. Despite these advances, we are still faced with numerous unanswered questions in the pathophysiology and management of these complex thrombocytopenic disorders.

Heparin-Induced Thrombocytopenia in the Critically Ill Patient

Heparin-induced thrombocytopenia (HIT) is associated with clinically significant morbidity and mortality. Patients who are critically ill are commonly thrombocytopenic and exposed to heparin. Although HIT should be considered, it is not usually the cause of thrombocytopenia in the medical-surgical ICU population. A systematic approach to the patient who is critically ill who has thrombocytopenia according to clinical features, complemented by appropriate laboratory confirmation, should lead to a reduction in inappropriate laboratory testing and reduce the use of more expensive and less reliable anticoagulants. If the patient is deemed as being at intermediate or high risk for HIT or if HIT is confirmed by means of the serotonin-release assay, heparin should be stopped, heparin-bonded catheters should be removed, and a direct antithrombin or fondaparinux should be initiated to reduce the risk of thrombosis. Warfarin is absolutely contraindicated in the acute phase of HIT; if administered, its effects must be reversed by using vitamin K.

HITs and misses in 100 years of heparin

Heparin was discovered 100 years ago, and the heparin-induced thrombocytopenia syndrome was described 40 years ago. That the most powerful anticoagulant of the last century can also produce the most extreme prothrombotic diathesis is but one of the paradoxes that surround heparin-induced thrombocytopenia. Standard treatment is alternative anticoagulation. Advances continue to be made regarding pathophysiology, prevention, and treatment. Currently, an epidemic of overdiagnosis threatens the well-being of patients, so efforts to educate clinicians on when and how to make this diagnosis are pressing.

Clinical and laboratory tests for the diagnosis of heparin-induced thrombocytopenia

A rapid diagnostic work-up is required in patients with suspected heparin-induced thrombocytopenia (HIT). However, diagnosis of HIT is challenging due to a number of practical issues and methodological limitations. Many laboratory tests and a few clinical scoring systems are available but the individual characteristics and the diagnostic accuracy of these are hard to appraise. The 4Ts score is a well evaluated clinical assessment tool with the potential to rule out HIT in many patients. Still, it requires experience and is subject to a relevant inter-observer variability. Immunoassays such as enzyme-linked immunosorbent assays or recently developed rapid assays are able to exclude HIT in a number of patients. But, accuracy of immunoassays differs depending on type of assay, threshold, antibody specificity and even manufacturer. Due to a comparatively low positive predictive value, HIT cannot be confirmed by immunoassays alone. In addition, only some of them are immediately accessible, particularly in small laboratories. While functional assays such as the serotonin release assay (SRA) and the heparin-induced platelet activation assay (HIPA) are considered as gold standard for diagnosis of HIT, they require a highly specialised laboratory. In addition, some of them are not adequately evaluated. In clinical practice, we recommend an integrated diagnostic approach combining not only clinical assessment (the 4Ts score) but immunoassays and functional assays as well. We propose a clear diagnostic algorithm supporting clinical decision-making. Furthermore, we provide an overview of all current laboratory techniques for HIT and discuss diagnostic pathways and strategies to reduce diagnostic errors, and future perspectives.

Biophysical tools to assess the interaction of PF4 with polyanions

The antigen in heparin-induced thrombocytopenia (HIT) is expressed on platelet factor 4 (PF4) when PF4 complexes with polyanions. In recent years, biophysical tools (e. g. circular dichroism spectroscopy, atomic force microscopy, isothermal titration calorimetry, x-ray crystallography, electron microscopy) have gained an important role to complement immunological and functional assays for better understanding the interaction of heparin with PF4. This allowed identification of those features that make PF4 immunogenic (e. g. a certain conformational change induced by the polyanion, a threshold energy of the complexes, the existence of multimeric complexes, a certain number of bonds formed by PF4 with the polyanion) and to characterize the morphology and thermal stability of complexes formed by the protein with polyanions. These findings and methods can now be applied to test new drugs for their potential to induce the HIT-like adverse drug effect by preclinical in vitro testing. The methods and techniques applied to characterize the antigen in HIT may also be helpful to better understand the mechanisms underlying other antibody-mediated disorders in thrombosis and hemostasis (e. g. acquired hemophilia, thrombotic thrombocytopenic purpura). Furthermore, understanding the mechanisms making the endogenous protein PF4 immunogenic may help to understand the mechanisms underlying other autoimmune disorders.

Management of heparin-induced thrombocytopenia

PURPOSE OF REVIEW

The purpose of this review is to summarize recent findings on heparin-induced thrombocytopenia (HIT), a prothrombotic disorder caused by platelet-activating IgG targeting platelet factor 4 (PF4)/polyanion complexes.

RECENT FINDINGS

HIT can explain unusual clinical events, including adrenal hemorrhages, arterial/intracardiac thrombosis, skin necrosis, anaphylactoid reactions, and disseminated intravascular coagulation. Sometimes, HIT begins/worsens after stopping heparin ('delayed-onset' HIT). Various HIT-mimicking disorders are recognized (e.g., acute disseminated intravascular coagulation/'shock liver' with limb ischemia). HIT has features of both B-cell and T-cell immune responses; uptake of PF4/heparin complexes into macrophages ('macropinocytosis') facilitates the anti-PF4/heparin immune response. Antibody-induced activation of monocytes and platelets via their FcγIIA receptors triggers an intense procoagulant response. Sometimes, HIT antibodies recognize PF4 bound to (platelet-associated) chondroitin sulfate, explaining how HIT might occur without concurrent or recent heparin (delayed-onset HIT, 'spontaneous HIT syndrome'). The molecular structure of HIT antigen(s) has been characterized, providing a rationale for future drug design to avoid HIT and improve its treatment. The poor correlation between partial thromboplastin time and plasma argatroban levels (risking subtherapeutic anticoagulation) and need for intravenous administration of argatroban have led to increasing 'off-label' treatment with fondaparinux or one of the direct oral anticoagulants.

SUMMARY

Understanding the molecular mechanisms and unusual clinical features of HIT will improve its management.

Synthetic oligosaccharides can replace animal-sourced low-molecular weight heparins

Low-molecular weight heparin (LMWH) is used clinically to treat clotting disorders. As an animal-sourced product, LMWH is a highly heterogeneous mixture, and its anticoagulant activity is not fully reversible by protamine. Furthermore, the reliability of the LMWH supply chain is a concern for regulatory agencies. We demonstrate the synthesis of heparin dodecasaccharides (12-mers) at the gram scale. In vitro experiments demonstrate that the anticoagulant activity of the 12-mers could be reversed using protamine. One of these, labeled as 12-mer-1, reduced the size of blood clots in the mouse model of deep vein thrombosis and attenuated circulating procoagulant markers in the mouse model of sickle cell disease. An ex vivo experiment demonstrates that the anticoagulant activity of 12-mer-1 could be reversed by protamine. 12-mer-1 was also examined in a nonhuman primate model to determine its pharmacodynamic parameters. A 7-day toxicity study in a rat model showed no toxic effects. The data suggest that a synthetic homogeneous oligosaccharide can replace animal-sourced LMWHs.

Implementation of a rapid HIT immunoassay at a university hospital - Retrospective analysis of HIT laboratory orders in patients with thrombocytopenia

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is a rare cause of thrombocytopenia and a potentially life-threatening adverse drug reaction. Clinical overdiagnosis of HIT results in costly laboratory tests and anticoagulation. Criteria and algorithms for diagnosis are established, but their translation into clinical practice is still challenging.

STUDY DESIGN AND METHODS

In a retrospective approach we studied all HIT related laboratory test requests within four years and evaluated data before (1st period, 24month) and after (2nd period, 24month) replacing particle gel immunoassay (PaGIA) and enzyme-linked immunosorbent assay (ELISA) by a chemiluminescent immunoassay (CLIA). HIT was confirmed by heparin-induced platelet activation (HIPA) test. Clinical pretest probability for HIT using an implemented simplified 4Ts score and platelet count were evaluated. Costs for laboratory tests and alternative anticoagulation were calculated.

RESULTS

In 1850 patients with suspected HIT, 2327 laboratory orders were performed. In 87.2% of these orders an intermediate/high simplified 4Ts score was found. Thrombocytopenia was present in 87.1%. After replacing PaGIA and ELISA by CLIA the number of immunological and functional laboratory tests was reduced by 38.2%. The number of positive HIT immunoassays declined from 22.6% to 6.0%, while the number of positive HIPA tests among positive immunological tests increased by 19%. Altogether, acute HIT was confirmed in 59 patients. A decline in the use of alternative anticoagulants was observed in the 2nd period.

CONCLUSION

Our study shows that in a university hospital setting HIT is well-known, but diagnosis requires a precise laboratory confirmation. Replacing PaGIA and ELISA by CLIA did not influence laboratory order behavior but results in reduced overall costs for laboratory diagnostics and alternative anticoagulation.

Anti-Platelet Factor 4/Heparin Antibody Formation Occurs Endogenously and at Unexpected High Frequency in Polycythemia Vera

Background

Myeloproliferative neoplasms (MPN) encounter thromboses due to multiple known risk factors. Heparin-induced thrombocytopenia (HIT) is a thrombotic syndrome mediated by anti-platelet factor 4 (PF4)/heparin antibodies with undetermined significance for thrombosis in MPN. We hypothesized that anti-PF4/heparin Ab might occur in MPN and promote thrombosis.

Methods

Anti-PF4/heparin antibodies were analyzed in 127 MPN patients including 76 PV and 51 ET. Screening, validation testing, and isotype testing of anti-PF4/heparin Ab were correlated with disease characteristics.

Results

Anti-PF4/heparin antibodies were detected in 21% of PV and 12% of ET versus 0.3–3% in heparin-exposed patients. Validation testing confirmed anti-PF4/heparin immunoglobulins in 15% of PV and 10% of ET. Isotype testing detected 9.2% IgG and 5.3% IgM in PV and exclusively IgM in ET. IgG-positive PV patients encountered thromboses in 57.1% suggesting anti-PF4/heparin IgG may contribute to higher risk for thrombosis in MPN. Overall, 45% of PV patients experienced thromboses with 11.8% positive for anti-PF4/heparin IgG versus 7.1% in PV without thrombosis.

Conclusion

Anti-PF4/heparin antibodies occur endogenously and more frequently in MPN than upon heparin exposure. Thrombotic risk increases in anti-PF4/heparin IgG-positive PV reflecting potential implications and calling for larger, confirmatory cohorts. Anti-PF4/heparin IgG should be assessed upon thrombosis in PV to facilitate avoidance of heparin in anti-PF4/heparin IgG-positive PV.

A decision model to estimate a risk threshold for venous thromboembolism prophylaxis in hospitalized medical patients

Essentials Low risk patients don't require venous thromboembolism (VTE) prophylaxis; low risk is unquantified. We used a Markov model to estimate the risk threshold for VTE prophylaxis in medical inpatients. Prophylaxis was cost-effective for an average medical patient with a VTE risk of ≥ 1.0%. VTE prophylaxis can be personalized based on patient risk and age/life expectancy.

SUMMARY

Background Venous thromboembolism (VTE) is a common preventable condition in medical inpatients. Thromboprophylaxis is recommended for inpatients who are not at low risk of VTE, but no specific risk threshold for prophylaxis has been defined. Objective To determine a threshold for prophylaxis based on risk of VTE. Patients/Methods We constructed a decision model with a decision-tree following patients for 3 months after hospitalization, and a lifetime Markov model with 3-month cycles. The model tracked symptomatic deep vein thromboses and pulmonary emboli, bleeding events and heparin-induced thrombocytopenia. Long-term complications included recurrent VTE, post-thrombotic syndrome and pulmonary hypertension. For the base case, we considered medical inpatients aged 66 years, having a life expectancy of 13.5 years, VTE risk of 1.4% and bleeding risk of 2.7%. Patients received enoxaparin 40 mg day-1 for prophylaxis. Results Assuming a willingness-to-pay (WTP) threshold of $100 000/ quality-adjusted life year (QALY), prophylaxis was indicated for an average medical inpatient with a VTE risk of ≥ 1.0% up to 3 months after hospitalization. For the average patient, prophylaxis was not indicated when the bleeding risk was > 8.1%, the patient's age was > 73.4 years or the cost of enoxaparin exceeded $60/dose. If VTE risk was < 0.26% or bleeding risk was > 19%, the risks of prophylaxis outweighed benefits. The prophylaxis threshold was relatively insensitive to low-molecular-weight heparin cost and bleeding risk, but very sensitive to patient age and life expectancy. Conclusions The decision to offer prophylaxis should be personalized based on patient VTE risk, age and life expectancy. At a WTP of $100 000/QALY, prophylaxis is not warranted for most patients with a 3-month VTE risk below 1.0%.

IVIg for Treatment of Severe Refractory Heparin-Induced Thrombocytopenia

BACKGROUND

Heparin-induced thrombocytopenia (HIT) complicated by severe thrombocytopenia and thrombosis can pose significant treatment challenges. Use of alternative anticoagulants in this setting may increase bleeding risks, especially in patients who have a protracted disease course. Additional therapies are lacking in this severely affected patient population.

METHODS

We describe three patients with HIT who had severe thromboembolism and prolonged thrombocytopenia refractory to standard treatment but who achieved an immediate and sustained response to IVIg therapy. The mechanism of action of IVIg was evaluated in these patients and in five additional patients with severe HIT. The impact of a common polymorphism (H/R 131) in the platelet IgG receptor FcγRIIa on IVIg-mediated inhibition of platelet activation was also examined.

RESULTS

At levels attained in vivo, IVIg inhibits HIT antibody-mediated platelet activation. The constant domain of IgG (Fc) but not the antigen-binding portion (Fab) is required for this effect. Consistent with this finding, IVIg had no effect on HIT antibody binding in a solid-phase HIT immunoassay (platelet factor 4 enzyme-linked immunoassay). The H/R131 polymorphism in FcγRIIa influences the susceptibility of platelets to IVIg treatment, with the HH131 genotype being most susceptible to IVIg-mediated inhibition of antibody-induced activation. However, at high doses of IVIg, activation of platelets of all FcγRIIa genotypes was significantly inhibited. All three patients did well on long-term anticoagulation therapy with direct oral anticoagulants.

CONCLUSIONS

These studies suggest that IVIg treatment should be considered in patients with HIT who have severe disease that is refractory to standard therapies.

Heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is an immune complication of heparin therapy caused by antibodies to complexes of platelet factor 4 (PF4) and heparin. Pathogenic antibodies to PF4/heparin bind and activate cellular FcγRIIA on platelets and monocytes to propagate a hypercoagulable state culminating in life-threatening thrombosis. It is now recognized that anti-PF4/heparin antibodies develop commonly after heparin exposure, but only a subset of sensitized patients progress to life-threatening complications of thrombocytopenia and thrombosis. Recent scientific developments have clarified mechanisms underlying PF4/heparin immunogenicity, disease susceptibility, and clinical manifestations of disease. Insights from clinical and laboratory findings have also been recently harnessed for disease prevention. This review will summarize our current understanding of HIT by reviewing pathogenesis, essential clinical and laboratory features, and management.

Synthesis of 3-O-Sulfated Oligosaccharides to Understand the Relationship between Structures and Functions of Heparan Sulfate

The sulfation at the 3-OH position of glucosamine is an important modification in forming structural domains for heparan sulfate to enable its biological functions. Seven 3-O-sulfotransferase isoforms in the human genome are involved in the biosynthesis of 3-O-sulfated heparan sulfate. As a rare modification present in heparan sulfate, the availability of 3-O-sulfated oligosaccharides is very limited. Here, we report the use of a chemoenzymatic synthetic approach to synthesize six 3-O-sulfated oligosaccharides, including three hexasaccharides and three octasaccharides. The synthesis was achieved by rearranging the enzymatic modification sequence to accommodate the substrate specificity of 3-O-sulfotransferase 3. We studied the impact of 3-O-sulfation on the conformation of the pyranose ring of 2-O-sulfated iduronic acid using NMR, and on the correlation between ring conformation and anticoagulant activity. We identified a novel octasaccharide that interacts with antithrombin and displays anti factor Xa activity. Interestingly, the octasaccharide displays a faster clearance rate than fondaparinux, an FDA-approved pentasaccharide drug, in a rat model, making this octasaccharide a potential short-acting anticoagulant drug candidate that could reduce bleeding risk. Having access to a set of critically important 3-O-sulfated oligosaccharides offers the potential to develop new heparan sulfate-based therapeutics.

Heparin-induced thrombocytopenia: research and clinical updates

Heparin-induced thrombocytopenia (HIT) remains an important diagnosis to consider in hospitalized patients developing thrombocytopenia. HIT is an immune-mediated prothrombotic disorder caused by antibodies to platelet factor 4 (PF4) and heparin. Recent basic scientific studies have advanced our understanding of disease pathogenesis through studies of the PF4/heparin structure, immune mechanisms, and cellular basis of thrombosis. Clinical advances have also occurred in areas of HIT prevention, description of disease variants, and diagnostic strategies. Emerging anticoagulants with the potential to change HIT treatment are evolving, although with limited data. This review will provide a current perspective on HIT pathogenesis, disease features, diagnostic strategies, and role of emerging therapies for the management of HIT.