Clinical outcomes in a cohort of patients with heparin-induced thrombocytopenia

Proteomic profiling for biomarker discovery in heparin-induced thrombocytopenia

ABSTRACT

New analytical techniques can assess hundreds of proteins simultaneously with high sensitivity, facilitating the observation of their complex interplay and role in disease mechanisms. We hypothesized that proteomic profiling targeting proteins involved in thrombus formation, inflammation, and the immune response would identify potentially new biomarkers for heparin-induced thrombocytopenia (HIT). Four existing panels of the Olink proximity extension assay covering 356 proteins involved in thrombus formation, inflammation, and immune response were applied to randomly selected patients with suspected HIT (confirmed HIT, n = 32; HIT ruled out, n = 38; and positive heparin/platelet factor 4 [H/PF4] antibodies, n = 28). The relative difference in protein concentration was analyzed using a linear regression model adjusted for sex and age. To confirm the test results, soluble P-selectin was determined using enzyme-linked immunosorbent assay (ELISA) in above mentioned patients and an additional second data set (n = 49). HIT was defined as a positive heparin-induced platelet activation assay (washed platelet assay). Among 98 patients of the primary data set, the median 4Ts score was 5 in patients with HIT, 4 in patients with positive H/PF4 antibodies, and 3 in patients without HIT. The median optical density of a polyspecific H/PF4 ELISA were 3.0, 0.9, and 0.3. Soluble P-selectin remained statistically significant after multiple test adjustments. The area under the receiver operating characteristic curve was 0.81 for Olink and 0.8 for ELISA. Future studies shall assess the diagnostic and prognostic value of soluble P-selectin in the management of HIT.

Outcomes of heparin-induced thrombocytopenia type II in aneurysmal subarachnoid hemorrhage patients: A US nationwide analysis

BACKGROUND

Despite the widespread use of heparin during and following endovascular procedures in the management of aneurysmal subarachnoid hemorrhage (SAH) patients, limited research has explored the incidence and impact of heparin-induced thrombocytopenia (HIT) on SAH.

METHODS

Descriptive statistics, multivariate regressions, and propensity score-matching were employed to compare clinical characteristics, comorbidities, interventions, complications, and outcomes of HIT in SAH patients identified within the US National Inpatient Sample database from 2010 to 2019.

RESULTS

Among 76 387 SAH patients from 2010 to 2019, 166 (0.22%) developed HIT. HIT was identified as a significant predictor of prolonged length of stay (OR 6.799, 95% CI 3.985 to 11.6, P<0.01) and poor functional outcomes (OR 2.541, 95% CI 1.628 to 3.966, P<0.01) after adjusting for relevant factors. HIT incidence was higher in patients with elevated SAH severity scores (1.42 vs 1.06, P<0.01), younger patients (58.04 vs 61.39 years, P=0.01), overweight individuals (0.4% vs 0.2%, P<0.01), those on long-term anticoagulants (10.84% vs 5.72%, P<0.01), or with a cerebrospinal fluid drainage device (external ventricular drain, ventriculoperitoneal shunt; P<0.01). HIT patients showed increased rates of endovascular coiling, ventricular drain placement, shunt placement, deep vein thrombosis, urinary tract infection, acute kidney injury, pulmonary embolism, venous sinus thrombosis, pneumonia, and cerebral vasospasm (all P<0.01).

CONCLUSION

SAH patients with HIT exhibited various comorbidities and increased rates of complications, which may contribute to extended hospital stays. This nationwide study aids clinical suspicion and highlights HIT's impact on SAH patients.

Fibrinogenolysis and fibrinolysis in vaccine-induced immune thrombocytopenia and thrombosis

BACKGROUND

Vaccine-induced immune thrombocytopenia and thrombosis (VITT) is a rare syndrome associated with adenoviral vector vaccines for COVID-19. The syndrome is characterized by thrombosis, anti-platelet factor 4 (PF4) antibodies, thrombocytopenia, high D-dimer, and hypofibrinogenemia.

OBJECTIVES

To investigate abnormalities in fibrinolysis that contribute to the clinical features of VITT.

METHODS

Plasma samples from 18 suspected VITT cases were tested for anti-PF4 by ELISA and characterized as meeting criteria for VITT (11/18) or deemed unlikely (7/18; non-VITT). Antigen levels of PAI-1, factor XIII (FXIII), plasmin-α2antiplasmin (PAP), and inflammatory markers were quantified. Plasmin generation was quantified by chromogenic substrate. Western blotting was performed with antibodies to fibrinogen, FXIII-A, and plasminogen.

RESULTS

VITT patients 10/11 had scores indicative of overt disseminated intravascular coagulation, while 0/7 non-VITT patients met the criteria. VITT patients had significantly higher levels of inflammatory markers, IL-1β, IL-6, IL-8, TNFα, and C-reactive protein. In VITT patients, both fibrinogen and FXIII levels were significantly lower, while PAP and tPA-mediated plasmin generation were higher compared to non-VITT patients. Evidence of fibrinogenolysis was observed in 9/11 VITT patients but not in non-VITT patients or healthy controls. Fibrinogen degradation products were apparent, with obvious cleavage of the fibrinogen α-chain. PAP complex was evident in those VITT patients with fibrinogenolysis, but not in non-VITT patients or healthy donors.

CONCLUSION

VITT patients show evidence of overt disseminated intravascular coagulation and fibrinogenolysis, mediated by dysregulated plasmin generation, as evidenced by increased PAP and plasmin generation. These observations are consistent with the clinical presentation of both thrombosis and bleeding in VITT.

Antibodies against platelet factor 4 and the risk of cerebral venous sinus thrombosis in patients with vaccine-induced immune thrombotic thrombocytopenia

BACKGROUND

Vaccine-induced immune thrombotic thrombocytopenia (VITT) is a rare complication of adenoviral vector-based vaccines against SARS-CoV-2. This syndrome is caused by antibodies against platelet factor 4 (PF4; CXCL4) that lead to platelet activation and is characterized by thrombocytopenia and thrombosis in unusual locations, including cerebral venous sinus thrombosis (CVST). VITT can be classified based on anti-PF4 antibodies properties in vitro: those that require PF4 to activate platelets (PF4-dependent) and those that can activate platelets without additional PF4 (PF4-independent) in the serotonin release assay.

OBJECTIVES

We aim to characterize the relationship of VITT platelet-activating profiles with CVST.

METHODS

We conducted a retrospective cohort study involving patients with confirmed VITT who were tested between March and June 2021. Data were collected with an anonymized form and cases were identified as VITT with high clinical suspicion according to platelet activation assays. Anti-PF4 antibody binding regions on PF4 were further characterized with alanine scanning mutagenesis.

RESULTS

Of the patients with confirmed VITT (n = 39), 17 (43.6%) had PF4-dependent antibodies and 22 (56.4%) had PF4-independent antibodies. CVST occurred almost exclusively in PF4-independent patients (11 of 22 vs 1 of 17; P < .05). Additionally, PF4-independent antibodies bound to 2 distinct epitopes on PF4, the heparin-binding region and a site typical for heparin-induced thrombocytopenia antibodies, whereas PF4-dependent antibodies bound to only the heparin-binding region.

CONCLUSION

These findings suggest that VITT antibodies that cause PF4-independent platelet activation represent a unique subset of patients more likely to be associated with CVST, possibly due to the 2 different types of anti-PF4 antibodies.

Novel Strategy to Combat the Procoagulant Phenotype in Heparin-Induced Thrombocytopenia Using 12-LOX Inhibition

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is a major concern for all individuals that undergo cardiac bypass surgeries or require prolonged heparin exposure. HIT is a life- and limb-threatening adverse drug reaction with an immune response following the formation of ultra-large immune complexes that drive platelet activation through the receptor FcγRIIA. Thrombotic events remain high following the standard of care treatment with anticoagulants, while increasing risk of bleeding complications. This study sought to investigate a novel approach to treatment of HIT. Recent reports demonstrate increased procoagulant activity in HIT; however, these reports required analysis ex vivo, and relevance in vivo remains unclear.

METHODS

Using human and mouse model systems, we investigated the cooperativity of PARs (protease-activated receptors) and FcγRIIA in HIT. We challenged humanized FcγRIIA transgenic mice with or without endogenous mouse Par4 (denoted as IIA-Par4+/+ or IIA-Par4-/-, respectively) with a well-established model IgG immune complex (anti [α]-CD9). Furthermore, we assessed the procoagulant phenotype and efficacy to treat HIT utilizing inhibitor of 12-LOX (12[S]-lipoxygenase), VLX-1005, previously reported to decrease platelet activation downstream of FcγRIIA and PAR4, using the triple allele HIT mouse model.

RESULTS

IIA-Par4+/+ mice given αCD9 were severely thrombocytopenic, with extensive platelet-fibrin deposition in the lung. In contrast, IIA-Par4-/- mice had negligible thrombocytopenia or pulmonary platelet-fibrin thrombi. We observed that pharmacological inhibition of 12-LOX resulted in a significant reduction in both platelet procoagulant phenotype ex vivo, and thrombocytopenia and thrombosis in our humanized mouse model of HIT in vivo.

CONCLUSIONS

These data demonstrate for the first time the need for dual platelet receptor (PAR and FcγRIIA) stimulation for fibrin formation in HIT in vivo. These results extend our understanding of HIT pathophysiology and provide a scientific rationale for targeting the procoagulant phenotype as a possible therapeutic strategy in HIT.

Treatment of thrombocytopenia and thrombosis in HIT in mice using deglycosylated KKO: a novel therapeutic?

Heparin-induced thrombocytopenia (HIT) is characterized by thrombocytopenia associated with a highly prothrombotic state due to the development of pathogenic antibodies that recognize human platelet factor 4 (hPF4) complexed with various polyanions. Although nonheparin anticoagulants are the mainstay of care in HIT, subsequent bleeding may develop, and the risk of developing new thromboembolic events remain. We previously described a mouse immunoglobulin G2bκ (IgG2bκ) antibody KKO that mimics the sentinel features of pathogenic HIT antibodies, including binding to the same neoepitope on hPF4-polyanion complexes. KKO, like HIT IgGs, activates platelets through FcγRIIA and induces complement activation. We then questioned whether Fc-modified KKO could be used as a novel therapeutic to prevent or treat HIT. Using the endoglycosidase EndoS, we created deglycosylated KKO (DGKKO). Although DGKKO retained binding to PF4-polyanion complexes, it inhibited FcγRIIA-dependent activation of PF4-treated platelets triggered by unmodified KKO, 5B9 (another HIT-like monoclonal antibody), and IgGs isolated from patients with HIT. DGKKO also decreased complement activation and deposition of C3c on platelets. Unlike the anticoagulant fondaparinux, injection of DGKKO into HIT mice lacking mouse PF4, but transgenic for hPF4 and FcγRIIA, prevented and reversed thrombocytopenia when injected before or after unmodified KKO, 5B9, or HIT IgG. DGKKO also reversed antibody-induced thrombus growth in HIT mice. In contrast, DGKKO was ineffective in preventing thrombosis induced by IgG from patients with the HIT-related anti-PF4 prothrombotic disorder, vaccine-induced immune thrombotic thrombocytopenia. Thus, DGKKO may represent a new class of therapeutics for targeted treatment of patients with HIT.

Novel Knowledge about Molecular Mechanisms of Heparin-Induced Thrombocytopenia Type II and Treatment Targets

Heparin-induced thrombocytopenia type II (HIT II), as stated in the literature, occurs in about 3% of all patients and in 0.1-5% of surgical patients. Thrombosis develops in 20-64% of patients with HIT. The mortality rate in HIT II has not decreased using non-heparin treatment with anticoagulants such as argatroban and lepirudin. An improved understanding of the pathophysiology of HIT may help identify targeted therapies to prevent thrombosis without subjecting patients to the risk of intense anticoagulation. The review will summarize the current knowledge about the pathogenesis of HIT II, potential new therapeutic targets related to it, and new treatments being developed. HIT II pathogenesis involves multi-step immune-mediated pathways dependent on the ratio of PF4/heparin and platelet, monocyte, neutrophil, and endothelium activation. For years, only platelets were known to take part in HIT II development. A few years ago, specific receptors and signal-induced pathways in monocytes, neutrophils and endothelium were revealed. It had been shown that the cells that had become active realised different newly formed compounds (platelet-released TF, TNFα, NAP2, CXCL-7, ENA-78, platelet-derived microparticles; monocytes-TF-MPs; neutrophils-NETs), leading to additional cell activation and consequently thrombin generation, resulting in thrombosis. Knowledge about FcγIIa receptors on platelets, monocytes, neutrophils and FcγIIIa on endothelium, chemokine (CXCR-2), and PSGL-1 receptors on neutrophils could allow for the development of a new non-anticoagulant treatment for HIT II. IgG degradation, Syk kinase and NETosis inhibition are in the field of developing new treatment possibilities too. Accordingly, IdeS and DNases-related pathways should be investigated for better understanding of HIT pathogenesis and the possibilities of being the HIT II treatment targets.

Modulation of ultralarge immune complexes in heparin-induced thrombocytopenia

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is a serious thrombotic disorder caused by ultralarge immune complexes (ULICs) containing platelet factor 4 (PF4) and heparin that form the HIT antigen, together with a subset of anti-PF4 antibodies. ULICs initiate prothrombotic responses by engaging Fcγ receptors on platelets, neutrophils, and monocytes. Contemporary anti-thrombotic therapy for HIT is neither entirely safe nor entirely successful and acts downstream of ULIC formation and Fcγ receptor-initiated generation of thrombin.

OBJECTIVES

To determine whether HIT antigen and ULIC formation and stability could be modified favorably by inhibiting PF4-heparin interactions with fondaparinux, together with blocking formation of PF4 tetramers using a humanized monoclonal anti-PF4 antibody (hRTO).

METHODS

Results: The combination of fondaparinux and hRTO inhibited HIT antigen formation, promoted antigen dissociation, inhibited ULIC formation, and promoted ULIC disassembly at concentrations below the effective concentration of either alone and blocked Fcγ receptor-dependent induction of factor Xa activity by monocytic THP1 cells and activation of human platelets in whole blood. Combined with hRTO, fondaparinux inhibited HIT antigen and immune complex formation and activation through Fcγ receptors at concentrations at or below those used clinically to inhibit FXa coagulant activity.

CONCLUSIONS

HIT antigen and immune complexes are dynamic and amenable to modulation. Fondaparinux can be converted from an anticoagulant that acts at a downstream amplification step into a rationale, disease-specific intervention that blocks ULIC formation. Interventions that prevent ULIC formation and stability might increase the efficacy, permit use of lower doses, shorten the duration of antithrombotic therapy, and help prevent this serious thrombotic disorder.

Neurological autoimmune diseases following vaccinations against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2): A follow-up study

BACKGROUND AND PURPOSE

Population-based studies suggest severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines may trigger neurological autoimmunity including immune-mediated thrombotic thrombocytopenia. Long-term characterization of cases is warranted to facilitate patient care and inform vaccine-hesitant individuals.

METHODS

In this single-center prospective case study with a median follow-up of 387 days long-term clinical, laboratory and imaging characteristics of patients with neurological autoimmunity diagnosed in temporal association (≤6 weeks) with SARS-CoV-2 vaccinations are reported.

RESULTS

Follow-up data were available for 20 cases (central nervous system demyelinating diseases n = 8, inflammatory peripheral neuropathies n = 4, vaccine-induced immune thrombotic thrombocytopenia n = 3, myositis n = 2, myasthenia n = 1, limbic encephalitis n = 1, giant cell arteritis n = 1). Following therapy, the overall disability level improved (median modified Rankin Scale at diagnosis 3 vs. 1 at follow-up). The condition of two patients worsened despite immunosuppressants possibly related to their autoimmune diagnoses (limbic encephalitis n = 1, giant cell arteritis n = 1). At 12 months' follow-up, 12 patients achieved complete clinical remissions with partial responses in five and stable disease in one case. Correspondingly, autoimmune antibodies were non-detectable or titers had significantly lowered in all, and repeat imaging revealed radiological responses in most cases. Under vigilant monitoring 15 patients from our cohort underwent additional SARS-CoV-2 vaccinations (BNT162b2 n = 12, mRNA-1273 n = 3). Most patients (n = 11) received different vaccines than prior to diagnosis of neurological autoimmunity. Except for one short-lasting relapse, which responded well to steroids, re-vaccinations were well tolerated.

CONCLUSIONS

In this study long-term characteristics of neurological autoimmunity encountered after SARS-CoV-2 vaccinations are defined. Outcome was favorable in most cases. Re-vaccinations were well tolerated and should be considered on an individual risk/benefit analysis.

Early high-dose intravenous immunoglobulin for refractory heparin-induced thrombocytopenia with stroke: Two case reports

BACKGROUND

High-dose intravenous immunoglobulin (IVIg) can be effective for patients with refractory autoimmune heparin-induced thrombocytopenia (HIT). We report two patients with autoimmune HIT (aHIT) successfully treated with early high-dose IVIg.

CASE DESCRIPTION

Case 1 was a 48-year-old male who had persisting HIT with recurrent ischemic stroke after mitral valve replacement. Case 2 was a 71-year-old male who had flush heparin HIT with cerebral venous thrombosis after total hip arthroplasty. High-dose IVIg was administered 6 and 4 days after starting argatroban due to non-improved thrombocytopenia and persistently high D-dimer values, respectively. Both patients achieved favorable functional recovery at discharge as well as improvements of thrombocytopenia and hypercoagulation.

CONCLUSIONS

Early high-dose IVIg may be effective for patients with aHIT and hypercoagulability.

A machine-learning model for reducing misdiagnosis in heparin-induced thrombocytopenia: A prospective, multicenter, observational study

BACKGROUND

Diagnosing heparin-induced thrombocytopenia (HIT) at the bedside remains challenging, exposing a significant number of patients at risk of delayed diagnosis or overtreatment. We hypothesized that machine-learning algorithms could be utilized to develop a more accurate and user-friendly diagnostic tool that integrates diverse clinical and laboratory information and accounts for complex interactions.

METHODS

We conducted a prospective cohort study including 1393 patients with suspected HIT between 2018 and 2021 from 10 study centers. Detailed clinical information and laboratory data were collected, and various immunoassays were conducted. The washed platelet heparin-induced platelet activation assay (HIPA) served as the reference standard.

FINDINGS

HIPA diagnosed HIT in 119 patients (prevalence 8.5%). The feature selection process in the training dataset (75% of patients) yielded the following predictor variables: (1) immunoassay test result, (2) platelet nadir, (3) unfractionated heparin use, (4) CRP, (5) timing of thrombocytopenia, and (6) other causes of thrombocytopenia. The best performing models were a support vector machine in case of the chemiluminescent immunoassay (CLIA) and the ELISA, as well as a gradient boosting machine in particle-gel immunoassay (PaGIA). In the validation dataset (25% of patients), the AUROC of all models was 0.99 (95% CI: 0.97, 1.00). Compared to the currently recommended diagnostic algorithm (4Ts score, immunoassay), the numbers of false-negative patients were reduced from 12 to 6 (-50.0%; ELISA), 9 to 3 (-66.7%, PaGIA) and 14 to 5 (-64.3%; CLIA). The numbers of false-positive individuals were reduced from 87 to 61 (-29.8%; ELISA), 200 to 63 (-68.5%; PaGIA) and increased from 50 to 63 (+29.0%) for the CLIA.

INTERPRETATION

Our user-friendly machine-learning algorithm for the diagnosis of HIT (https://toradi-hit.org) was substantially more accurate than the currently recommended diagnostic algorithm. It has the potential to reduce delayed diagnosis and overtreatment in clinical practice. Future studies shall validate this model in wider settings.

FUNDING

Swiss National Science Foundation (SNSF), and International Society on Thrombosis and Haemostasis (ISTH).

Acute limb ischemia due to severe heparin-included thrombocytopenia with thrombosis during puerperium

We present the case of a 39-year-old pregnant woman who had intrauterine fetal death and imminent uterine rupture and underwent cesarean section. She also underwent catheter embolization for hemorrhagic shock due to bleeding from the uterine artery, and heparin-containing saline was used. On day 7 of hospitalization, she felt severe pain in her right lower leg, and computed tomography (CT) revealed focal nonocclusive thrombus formations in the right common and external iliac artery. After intravenous heparin administration, she suddenly developed dyspnea, her blood pressure dropped, and her platelet count decreased. We diagnosed her with heparin-induced thrombocytopenia (HIT). Although we discontinued heparin and switched to argatroban, CT after 5 days revealed subtotal occlusion of the right iliac artery by a massive thrombus. We performed surgical thrombectomy using a Fogarty catheter, but blood flow was not restored. Therefore, we administered urokinase continuously with catheter-directed thrombolysis (CDT). The thrombus in the iliac artery gradually cleared and was successfully eliminated. However, the patient developed gangrene in her right lower leg, and we decided to perform an above-knee amputation of the right leg. She was discharged with a prosthetic leg and prescribed 15 mg of rivaroxaban per day.

Learning objective

HIT is a known serious side effect of heparin administration, and it can sometimes be fatal. HIT treatment using aggressive thrombectomy procedures may be ineffective since such procedures may accelerate thrombus formation when the coagulation cascade is highly activated. In this case, CDT may have to be considered as the first-line treatment before Fogarty thrombectomy when argatroban therapy fails.

Minimal role for the alternative pathway in complement activation by HIT immune complexes

BACKGROUND

Anti-platelet factor 4 (PF4)/heparin immune complexes that cause heparin-induced thrombocytopenia (HIT) activate complement via the classical pathway. Previous studies have shown that the alternative pathway of complement substantially amplifies the classical pathway of complement activation through the C3b feedback cycle.

OBJECTIVES

These studies sought to examine the contributions of the alternative pathway to complement activation by HIT antibodies.

METHODS

Using IgG monoclonal (KKO) and/or patient-derived HIT antibodies, we compared the effects of classical pathway (BBK32 and C1-esterase inhibitor [C1-INH]), alternative pathway (anti-factor B [fB] or factor D [fD] inhibitor) or combined classical and alternative pathway inhibition (soluble complement receptor 1 [sCR1]) in whole blood or plasma.

RESULTS

Classical pathway inhibitors BBK32 and C1-INH and the combined classical/alternative pathway inhibitor sCR1 prevented KKO/HIT immune complex-induced complement activation, including release of C3 and C5 activation products, binding of immune complexes to B cells, and neutrophil activation. The alternative pathway inhibitors fB and fD, however, did not affect complement activation by KKO/HIT immune complexes. Similarly, alternative pathway inhibition had no effect on complement activation by unrelated immune complexes consisting of anti-dinitrophenyl (DNP) antibody and the multivalent DNP--keyhole limpet hemocyanin antigen.

CONCLUSIONS

Collectively, these findings suggest the alternative pathway contributes little in support of complement activation by HIT immune complexes. Additional in vitro and in vivo studies are required to examine if this property is shared by most IgG-containing immune complexes or if predominance of the classic pathway is limited to immune complexes composed of multivalent antigens.

Treatment of drug-induced immune thrombocytopenias

Several therapeutic agents can cause thrombocytopenia by either immune-mediated or non-immune-mediated mechanisms. Non-immune-mediated thrombocytopenia is due to direct toxicity of drug molecules to platelets or megakaryocytes. Immune-mediated thrombocytopenia, on the other hand, involves the formation of antibodies that react to platelet-specific glycoprotein complexes, as in classic drug-induced immune thrombocytopenia (DITP), or to platelet factor 4, as in heparin-induced thrombocytopenia (HIT) and vaccine-induced immune thrombotic thrombocytopenia (VITT). Clinical signs include a rapid drop in platelet count, bleeding or thrombosis. Since the patient's condition can deteriorate rapidly, prompt diagnosis and management are critical. However, the necessary diagnostic tests are only available in specialized laboratories. Therefore, the most demanding step in treatment is to identify the agent responsible for thrombocytopenia, which often proves difficult because many patients are taking multiple medications and have comorbidities that can themselves also cause thrombocytopenia. While DITP is commonly associated with an increased risk of bleeding, HIT and VITT have a high mortality rate due to the high incidence of thromboembolic complications. A structured approach to drug-associated thrombocytopenia/thrombosis can lead to successful treatment and a lower mortality rate. In addition to describing the treatment of DITP, HIT, VITT, and vaccine-associated immune thrombocytopenia, this review also provides the pathophysiological and clinical information necessary for correct patient management.

Treatment of chemotherapy-induced thrombocytopenia in patients with non-hematologic malignancies

Chemotherapy-induced thrombocytopenia (CIT) is a common complication of the treatment of non-hematologic malignancies. Many patient-related variables (e.g., age, tumor type, number of prior chemotherapy cycles, amount of bone marrow tumor involvement) determine the extent of CIT. CIT is related to the type and dose of chemotherapy, with regimens containing gemcitabine, platinum, or temozolomide producing it most commonly. Bleeding and the need for platelet transfusions in CIT are rather uncommon except in patients with platelet counts below 25x10⁹/L in whom bleeding rates increase significantly and platelet transfusions are the only treatment. Nonetheless, platelet counts below 70x10⁹/L present a challenge. In patients with such counts, it is important to exclude other causes of thrombocytopenia (medications, infection, thrombotic microangiopathy, post-transfusion purpura, coagulopathy and immune thrombocytopenia). If these are not present, the common approach is to reduce chemotherapy dose intensity or switch to other agents. Unfortunately decreasing relative dose intensity is associated with reduced tumor response and remission rates. Thrombopoietic growth factors (recombinant human thrombopoietin, pegylated human megakaryocyte growth and development factor, romiplostim, eltrombopag, avatrombopag and hetrombopag) improve pretreatment and nadir platelet counts, reduce the need for platelet transfusions, and enable chemotherapy dose intensity to be maintained. National Comprehensive Cancer Network guidelines permit their use but their widespread adoption awaits adequate phase III randomized, placebo-controlled studies demonstrating maintenance of relative dose intensity, reduction of platelet transfusions and bleeding, and possibly improved survival. Their potential appropriate use also depends on consensus by the oncology community as to what constitutes an appropriate pretreatment platelet count as well as identification of patient-related and treatment variables that might predict bleeding.

Cerebral Venous Thrombosis in Patients With Heparin-Induced Thrombocytopenia a Systematic Review

BACKGROUND

Cerebral venous thrombosis (CVT) has recently been reported as a common thrombotic manifestation in association with vaccine-induced thrombotic thrombocytopenia, a syndrome that mimics heparin-induced thrombocytopenia (HIT) and occurs after vaccination with adenovirus-based SARS-CoV-2 vaccines. We aimed to systematically review the incidence, clinical features, and prognosis of CVT occurring in patients with HIT.

METHODS

The study protocol was registered with PROSPERO (CRD42021249652). MEDLINE, EMBASE and Cochrane CENTRAL were searched up to June 1, 2021 for HIT case series including >20 patients, or any report of HIT-related CVT. Demographic, neuroradiological, clinical, and mortality data were retrieved. Meta-analysis of proportions with random-effect modeling was used to derive rate of CVT in HIT and in-hospital mortality. Pooled estimates were compared with those for CVT without HIT and HIT without CVT, to determine differences in mortality.

RESULTS

From 19073 results, we selected 23 case series of HIT (n=1220) and 27 cases of HIT-related CVT (n=27, 71% female). CVT developed in 1.6% of 1220 patients with HIT (95% CI,1.0%-2.5%, I²=0%). Hemorrhagic brain lesions occurred in 81.8% of cases of HIT-related CVT and other concomitant thrombosis affecting other vascular territory was reported in 47.8% of cases. In-hospital mortality was 33.3%. HIT-related CVT carried a 29% absolute increase in mortality rate compared with historical CVT controls (33.3% versus 4.3%, P<0.001) and a 17.4% excess mortality compared with HIT without CVT (33.3% versus 15.9%, P=0.046).

CONCLUSIONS

CVT is a rare thrombotic manifestation in patients with HIT. HIT-related CVT has higher rates of intracerebral hemorrhage and a higher mortality risk, when compared with CVT in historical controls. The recently reported high frequency of CVT in patients with vaccine-induced thrombotic thrombocytopenia was not observed in HIT, suggesting that additional pathophysiological mechanisms besides anti-platelet factor-4 antibodies might be involved in vaccine-induced thrombotic thrombocytopenia-related CVT.

Bleeding is associated with intravenous immunoglobulin and therapeutic plasma exchange use in heparin‐induced thrombocytopenia: A propensity matched analysis

Intravenous immunoglobulin (IVIG) and therapeutic plasma exchange (TPE) are used in select cases with heparin‐induced thrombocytopenia (HIT). In a cross‐sectional analysis, a propensity matched sample was generated by IVIG or TPE treatment status to assess the primary outcome of mortality. In 500 HIT cases, IVIG or TPE was not associated with increased mortality (OR = 1.46; 95% CI: 0.81–2.63, p = 0.2052) but was associated with a higher likelihood of major bleeding (OR = 1.75; 95% CI: 1.03–2.96, p = 0.0376). The use of IVIG or TPE in HIT cases with bleeding contraindications to standard therapies should be further investigated.

Vaccine-induced immune thrombotic thrombocytopenia: what we know and do not know

The development of vaccines to fight COVID-19 has been a remarkable medical achievement. However, this global immunization effort has been complicated by a rare vaccine-related outcome characterized by thrombocytopenia and thrombosis in association with platelet-activating anti-platelet factor 4 antibodies. In this Spotlight, we will discuss the recently described complication of vaccine-induced immune thrombotic thrombocytopenia (VITT) occurring in response to certain COVID-19 vaccines. Although information about this clinical condition is rapidly evolving, we will summarize our current understanding of VITT.

Complement mediates binding and procoagulant effects of ultra-large HIT immune complexes

Heparin-induced thrombocytopenia (HIT) is a prothrombotic disorder mediated by ultra-large immune complexes (ULICs) containing IgG antibodies to a multivalent antigen composed of platelet factor 4 (PF4) and heparin. The limitations of current anti-thrombotic therapy in HIT supports the need to identify additional pathways that may be targets for therapy. Activation of FcgRIIA by HIT ULICs initiates diverse procoagulant cellular effector functions. HIT ULICs are also known to activate complement, but the contribution of this pathway to the pathogenesis of HIT has not been studied in detail. We observed that HIT ULICs physically interact with C1q in buffer and plasma, activate complement via the classical pathway, promote co-deposition of IgG and activated C3 complement fragments (C3c) on neutrophil and monocyte cell surfaces. Complement activation by ULICs, in turn, facilitates Fcg receptor(R)-independent monocyte tissue factor expression, enhances IgG binding to the cell surface FcgRs and promotes platelet adhesion to injured endothelium. Inhibition of the proximal, but not terminal, steps in the complement pathway, abrogates monocyte tissue factor expression by HIT ULICs. Together, these studies suggest a major role for complement activation in regulating Fc-dependent effector functions of HIT ULICs, identify potential non-anticoagulant targets for therapy, and provide insights into the broader roles of complement in immune complex-mediated thrombotic disorders.

Soluble glycoprotein VI is a predictor of major bleeding in patients with suspected heparin-induced thrombocytopenia

We have shown that patients with suspected heparin-induced thrombocytopenia (HIT) have a high incidence of major bleeding. Recent studies have implicated elevated soluble glycoprotein VI (sGPVI) levels as a potential risk factor for bleeding. We sought to determine if elevated sGPVI plasma levels are associated with major bleeding events in patients with suspected HIT. We used a cohort of 310 hospitalized adult patients with suspected HIT who had a blood sample collected at the time HIT was suspected. Plasma sGPVI levels were measured by using enzyme-linked immunosorbent assay. Patients were excluded who had received a platelet transfusion within 1 day of sample collection because of the high levels of sGPVI in platelet concentrates. We assessed the association of sGPVI (high vs low) with International Society on Thrombosis and Haemostasis major bleeding events by multivariable logistic regression, adjusting for other known risk factors for bleeding. Fifty-four patients were excluded due to recent platelet transfusion, leaving 256 patients for analysis. Eighty-nine (34.8%) patients had a major bleeding event. Median sGPVI levels were significantly elevated in patients with major bleeding events compared with those without major bleeding events (49.09 vs 31.93 ng/mL; P < .001). An sGPVI level >43 ng/mL was independently associated with major bleeding after adjustment for critical illness, sepsis, cardiopulmonary bypass surgery, and degree of thrombocytopenia (adjusted odds ratio, 2.81; 95% confidence interval, 1.51-5.23). Our findings suggest that sGPVI is associated with major bleeding in hospitalized patients with suspected HIT. sGPVI may be a novel biomarker to predict bleeding risk in patients with suspected HIT.

A population-based analysis on the use of therapeutic plasma exchange and intravenous immunoglobulin in heparin-induced thrombocytopenia

INTRODUCTION

In heparin-induced thrombocytopenia (HIT), selected patients are treated with therapies directed at the immune response, intravenous immunoglobulin (IVIG) and therapeutic plasma exchange (TPE). To determine IVIG and TPE characteristics and outcomes in HIT, we analyzed the National Inpatient Sample (NIS) database.

METHODS

In a population-based analysis of the NIS, we identified hospital discharges of adult patients with a HIT diagnosis. A two-level statistical analysis was performed comparing cases as follows 1) IVIG or TPE vs. none; and 2) IVIG vs. TPE. For each analysis, the primary outcome was in-hospital mortality. Secondary outcomes were thrombotic events, major bleeding, infections, hospital length of stay, and total charges.

RESULTS

Among 22,152 discharges with a HIT diagnosis, 77 (0.34%) and 52 (0.23%) received TPE and IVIG, respectively. In the first level analysis of TPE or IVIG vs. no treatment, TPE or IVIG treatment was associated with a higher likelihood of in-hospital mortality (OR = 1.85; 95%CI: 1.13-3.03, p = 0.0104), major bleeding (OR = 1.91; 95%CI: 1.25-2.93, p = 0.0030), gastrointestinal bleeding (OR = 1.89; 95%CI: 1.08-3.30, p = 0.0259), and infection (OR = 1.65; 95% CI:1.13-2.41, p = 0.0095). In the second-level analysis comparing IVIG vs. TPE, there were no significant differences in patient characteristics or outcomes in both unadjusted and adjusted analyses.

CONCLUSIONS

In this population-based analysis of HIT, we found similar outcomes of IVIG and TPE-treated cases. Given the small sample size, future studies are needed to confirm this observation.

Heparin-Induced Thrombocytopenia: A Focus on Thrombosis

Heparin-induced thrombocytopenia is an immune-mediated disorder caused by antibodies that recognize complexes of platelet factor 4 and heparin. Thrombosis is a central and unpredictable feature of this syndrome. Despite optimal management, disease morbidity and mortality from thrombosis remain high. The hypercoagulable state in heparin-induced thrombocytopenia is biologically distinct from other thrombophilic disorders in that clinical complications are directly attributable to circulating ultra-large immune complexes. In some individuals, ultra-large immune complexes elicit unchecked cellular procoagulant responses that culminate in thrombosis. To date, the clinical and biologic risk factors associated with thrombotic risk in heparin-induced thrombocytopenia remain elusive. This review will summarize our current understanding of thrombosis in heparin-induced thrombocytopenia with attention to its clinical features, cellular mechanisms, and its management.

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.

A systematic literature review on the use of platelet transfusions in patients with thrombocytopenia

Objective: Investigate globally, current treatment patterns, benefit-risk assessments, humanistic, societal and economic burden of platelet transfusion (PT). Methods: Publications from 1998 to June 27, 2018 were identified, based on databases searches including MEDLINE®; Embase and Cochrane Database of Systematic Reviews. Data from studies meeting pre-specified criteria were extracted and validated by independent reviewers. Data were obtained for efficacy and safety from randomized controlled trials (RCTs); data for epidemiology, treatment patterns, effectiveness, safety, humanistic and societal burden from real-world evidence (RWE) studies; and economic data from both. Results: A total of 3425 abstracts, 194 publications (190 studies) were included. PT use varied widely, from 0%-100% of TCP patients; 1.7%-24.5% in large studies (>1000 patients). Most were used prophylactically rather than therapeutically. 5 of 43 RCTs compared prophylactic PT with no intervention, with mixed results. In RWE studies PT generally increased platelet count (PC). This increase varied by patient characteristics and hence did not always translate into a clinically significant reduction in bleeding risk. Safety concerns included infection risk, alloimmunization and refractoriness with associated cost burden. Discussion: In RCTs and RWE studies there was significant heterogeneity in study design and outcome measures. In RWE studies, patients receiving PT may have been at higher risk than those not receiving PT creating potential bias. There were limited data on humanistic and societal burden. Conclusion: Although PTs are used widely for increasing PC in TCP, it is important to understand the limitations of PTs, and to explore the use of alternative treatment options where available.

Recognition of PF4-VWF complexes by heparin-induced thrombocytopenia antibodies contributes to thrombus propagation

Heparin-induced thrombocytopenia (HIT) is a prothrombotic disorder mediated by complexes between platelet factor 4 (PF4) and heparin or other polyanions, but the risk of thrombosis extends beyond exposure to heparin implicating other PF4 partners. We recently reported that peri-thrombus endothelium is targeted by HIT antibodies, but the binding site(s) has not been identified. We now show that PF4 binds at multiple discrete sites along the surface of extended strings of von Willebrand factor (VWF) released from the endothelium following photochemical injury in an endothelialized microfluidic system under flow. The HIT-like monoclonal antibody KKO and HIT patient antibodies recognize PF4-VWF complexes, promoting platelet adhesion and enlargement of thrombi within the microfluidic channels. Platelet adhesion to the PF4-VWF-HIT antibody complexes is inhibited by antibodies that block FcγRIIA or the glycoprotein Ib-IX complex on platelets. Disruption of PF4-VWF-HIT antibody complexes by drugs that prevent or block VWF oligomerization attenuate thrombus formation in a murine model of HIT. Together, these studies demonstrate assembly of HIT immune complexes along VWF strings released by injured endothelium that might propagate the risk of thrombosis in HIT. Disruption of PF4-VWF complex formation may provide a new therapeutic approach to HIT.

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.

Thrombotic Thrombocytopenic Purpura, Heparin-Induced Thrombocytopenia, and Disseminated Intravascular Coagulation

Hemostatic abnormalities are common among critically ill patients and are associated with a high risk of bleeding. The abnormalities range from isolated thrombocytopenia or prolongation of global coagulation assays to complex disease states, such as thrombotic microangiopathic syndromes, and can be associated with a wide range of conditions, including trauma, surgery, acute disease processes, cardiopulmonary bypass, and exposure to drugs and blood products. Prompt identification of underlying causes is important because treatment strategies vary. Moreover, prompt initiation of both supportive and specific treatments is vital to decrease the morbidity and mortality in the intensive care unit.

A Novel Diagnostic Algorithm for Heparin-Induced Thrombocytopenia in a Retrospective Cohort of Lung Transplant Recipients

INTRODUCTION

Heparin-induced thrombocytopenia (HIT) is characterized by thrombocytopenia and potential for thromboembolism. Lung transplant recipients are at risk of developing HIT due to heparin exposure peritransplant. We describe the incidence and impact of HIT in lung transplant recipient index hospital length of stay and survival.

DESIGN

A retrospective cohort was obtained from electronic medical records which were queried for all recipients treated with bivalirudin (institutional treatment of choice for HIT) between January 1, 2005, and February 16, 2017 (N = 1171). Patients who developed HIT >30 days after transplant or after their index transplant admission were excluded. A diagnostic algorithm was used retrospectively to determine clinical HIT with an intermediate or high pretest clinical suspicion ("4T" score ≥4) and either (1) positive anti-heparin-platelet-factor 4 (HPF4) assay and a positive functional platelet assay or (2) a positive HPF4 assay only, in patients who did not undergo cardiopulmonary bypass.

RESULTS

Among all lung transplant recipients, 2.1% were found to develop HIT in the peritransplant period (N = 25, mean = 88%) with a mean lung allocation score of 50.8 and an incidence of venous thromboembolism of 72%, most upper extremity in location. When matched with historical controls, patients with HIT had a longer overall index hospital length of stay of 43 days (P = .008). There was no difference in short- or long-term survival posttransplant.

CONCLUSION

Vigilance for the development of HIT in lung transplant recipients is necessary to prevent further morbidity from thromboembolic events. In our cohort, HIT increased hospital length of stay but did not appear to affect recipient survival.

The risk of major bleeding in patients with suspected heparin-induced thrombocytopenia

BACKGROUND

The presence of a hypercoagulable disorder such as heparin-induced thrombocytopenia (HIT) may protect against anticoagulant-associated bleeding.

OBJECTIVES

To determine the incidence of major bleeding in patients with suspected HIT.

METHODS

We performed a retrospective analysis of 310 patients suspected of having HIT from the Hospital of the University of Pennsylvania and an affiliated community hospital. We compared the cumulative incidence of major bleeding following suspicion for HIT by ultimate HIT status (HIT+ or HIT-) and exposure to an alternative anticoagulant (Tx+ or Tx-). Secondary outcomes included the incidence of new/progressive thrombosis and 30-day mortality.

RESULTS

The incidence of major bleeding was high in the HIT+Tx+, HIT- Tx+, and HIT-Tx- groups (35.7%, 44.0%, and 37.3%, respectively). The time to first major bleeding event did not differ between groups (P = .24). Factors associated with increased risk of major bleeding included intensive care unit admission (HR 2.24, 95% CI 1.44-3.47), platelet count < 25 × 109 /L (HR 2.13, 1.10-4.12), and renal dysfunction (HR 1.56, 1.06-2.27); 35.7% of HIT+Tx+, 13.8% HIT-Tx+, and 9.3% of HIT-Tx- patients experienced new or progressive thrombosis. Mortality was similar among the three groups (26.2% HIT+Tx+, 34.5% HIT-Tx+, and 26.7% of HIT-Tx- [P = .34]).

CONCLUSIONS

Among patients with suspected HIT, major bleeding was common regardless of HIT status. Contrary to our hypothesis, HIT+ patients were not protected from major bleeding. A better understanding of bleeding risk is needed to inform management decisions in patients with suspected HIT.

How the configurational changes influence on molecular characteristics. The alkyl 3-azido-2,3-dideoxy-D-hexopyranosides - Theoretical approach

In this paper we present two currents of our research. The first goal was the geometry optimization of the structures of derivatives of the alkyl 3-azido-2,3-dideoxy-D-hexopyranosides. Then, we examine the influence of the applied quantum methods on the values of molecular features describing these structures. We use two methods for geometry optimization: the semi-empirical PM7 method and DFT B3LYP/6-31++G* method. The results of comparison parameters of descriptors indicate that there are no statistical differences obtained from both methods. Thus, we recommend the PM7 method for geometry optimization of the derivatives of the alkyl 3-azido-2,3-dideoxy-D-hexopyranosides due to its time and computer resources requirements. Another part of the research was the examination, which groups of descriptors are the most suitable for identifying the similarities in the configuration, the substituents pattern and the molecular mass of 232 examined structures. To explore relation between configuration changes of the 3-azidosaccharides and influence of these changes on the molecular characteristic, we use hierarchical cluster analysis (HCA), where WHIM, 3D-MORSE, RDF and GETAWAY descriptors were selected. Depending on the group of descriptors, molecules are divided in various ways. In general, saccharide' structures are divided into groups based on the configuration of substituents (combination of epimers) or length of the O-glycoside chain. Never before, these saccharides derivatives, were investigated by chemometric analysis. The most problematic issue in experimental and theoretical research is the configuration of substituents in pyranoside ring. Due to vast number of configurations, it is possible to obtain massive amount of diverse structures. This problem concerns us and opens opportunity in investigation the effect of configuration on the parameter of molecules.

Therapeutic plasma exchange for management of heparin-induced thrombocytopenia: Results of an international practice survey

INTRODUCTION

Anti-heparin/platelet factor 4 antibody immune complexes resulting from heparin-induced thrombocytopenia (HIT) are removed by therapeutic plasma exchange (TPE). We sought to define TPE in HIT practice patterns using an international survey.

METHODS

A 31-item online survey was disseminated through the American Society for Apheresis. After institutional duplicate responses were eliminated, a descriptive analysis was performed.

RESULTS

The survey was completed by 94 respondents from 78 institutions in 18 countries. Twenty-nine institutions (37%) used TPE for HIT (YES cohort) and 49 (63%) did not (NO cohort). Most NO respondents (65%) cited "no requests received" as the most common reason for not using TPE. Of the 29 YES respondents, 10 (34%) gave incomplete information and were excluded from the final analysis, leaving 19 responses. Of these, 18 (95%) treated ≤10 HIT patients over a 2-year period. The most common indications were cardiovascular surgery (CS; 63%) and HIT-associated thrombosis (HT; 26%). The typical plasma volume processed was 1.0 (63% CS and 58% HT). For CS, the typical replacement fluid was plasma (42%) and for HT, it was determined on an individual basis (32%). For CS, patients were treated with a set number of TPE procedures (37%) or laboratory/clinical response (37%). For HT, the number of TPE procedures typically depended on laboratory/clinical response (42%).

CONCLUSION

In a minority of responding institutions, TPE is most commonly used in HIT to prophylactically treat patients who will undergo heparin re-exposure during CS. Prospective studies are needed to more clearly define the role of TPE in HIT.

Anticoagulating patients with high-risk acquired thrombophilias

Antiphospholipid syndrome (APS), heparin-induced thrombocytopenia, and paroxysmal nocturnal hemoglobinuria are 3 acquired thrombophilias that carry a high risk of venous and arterial thromboembolism. Management of these conditions has largely included anticoagulation with a vitamin K antagonist after an initial period of a parenteral anticoagulant, for as long as the thrombotic risk is still present. The available evidence for the use of direct oral anticoagulants (DOACs) is limited and primarily consists of case series and cohort studies, which are summarized in this chapter. Randomized trials evaluating DOACs in patients with APS are reviewed. Further research is needed prior to widely adopting DOACs for use in these high-risk acquired thrombophilias; however, there may be selected low-risk subgroups where DOAC use is possible after careful consideration and patient discussion.

American Society of Hematology 2018 guidelines for management of venous thromboembolism: heparin-induced thrombocytopenia

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is an adverse drug reaction mediated by platelet-activating antibodies that target complexes of platelet factor 4 and heparin. Patients are at markedly increased risk of thromboembolism.

OBJECTIVE

These evidence-based guidelines of the American Society of Hematology (ASH) are intended to support patients, clinicians, and other health care professionals in their decisions about diagnosis and management of HIT.

METHODS

ASH formed a multidisciplinary guideline panel balanced to minimize potential bias from conflicts of interest. The McMaster University GRADE Centre supported the guideline development process, including updating or performing systematic evidence reviews. The panel prioritized clinical questions and outcomes according to their importance for clinicians and patients. The Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach was used to assess evidence and make recommendations, which were subject to public comment.

RESULTS

The panel agreed on 33 recommendations. The recommendations address screening of asymptomatic patients for HIT, diagnosis and initial management of patients with suspected HIT, treatment of acute HIT, and special situations in patients with acute HIT or a history of HIT, including cardiovascular surgery, percutaneous cardiovascular intervention, renal replacement therapy, and venous thromboembolism prophylaxis.

CONCLUSIONS

Strong recommendations include use of the 4Ts score rather than a gestalt approach for estimating the pretest probability of HIT and avoidance of HIT laboratory testing and empiric treatment of HIT in patients with a low-probability 4Ts score. Conditional recommendations include the choice among non-heparin anticoagulants (argatroban, bivalirudin, danaparoid, fondaparinux, direct oral anticoagulants) for treatment of acute HIT.

Anticoagulating patients with high-risk acquired thrombophilias

Antiphospholipid syndrome (APS), heparin-induced thrombocytopenia, and paroxysmal nocturnal hemoglobinuria are 3 acquired thrombophilias that carry a high risk of venous and arterial thromboembolism. Management of these conditions has largely included anticoagulation with a vitamin K antagonist after an initial period of a parenteral anticoagulant, for as long as the thrombotic risk is still present. The available evidence for the use of direct oral anticoagulants (DOACs) is limited and primarily consists of case series and cohort studies, which are summarized in this chapter. Randomized trials evaluating DOACs in patients with APS are reviewed. Further research is needed prior to widely adopting DOACs for use in these high-risk acquired thrombophilias; however, there may be selected low-risk subgroups where DOAC use is possible after careful consideration and patient discussion.

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.

Intravenous immunoglobulin as an adjunct therapy in persisting heparin-induced thrombocytopenia

Heparin induced thrombocytopenia (HIT) is a serious adverse drug reaction caused by transient antibodies against platelet factor 4 (PF4)/heparin complexes, resulting in platelet activation and potentially fatal arterial and/or venous thrombosis. Most cases of HIT respond to cessation of heparin and administration of an alternative non-heparin anticoagulant, but there are cases of persisting HIT, defined as thrombocytopenia due to platelet activation/consumption for greater than seven days despite standard therapy. These patients remain at high risk for thrombotic events, which may result in limb-loss and mortality. Intravenous immunoglobulin (IVIg) has been proposed as an adjunct therapy for these refractory cases based on its ability to saturate FcγRIIa receptors on platelets, thus preventing HIT antibody binding and platelet activation. We describe 2 cases of persisting HIT (strongly positive antigen and functional assays, and persisting thrombocytopenia >7 days) with rapid clinical response to IVIg. We performed in-vitro experiments to support IVIg response. Healthy donor platelets (1 × 10e6) were treated with PF4 (3.75 μg/mL) for 20 min followed by 1-hour incubation with patients' sera. Platelet activation with and without addition of IVIg (levels equivalent to those reached in a patient after treatment with 2 gm/Kg) was evaluated in the PF4-dependent P-selectin expression assay (PEA). A significantly decreased platelet activation was demonstrated after the addition of IVIg to both patient samples, which correlated well with the rapid clinical response that each patient experienced. Thus, our study supports the use of IVIg as an adjunct therapy for persisting HIT.