Gender imbalance and risk factor interactions in heparin-induced thrombocytopenia

Paradoxical Worsening of Cerebral Venous Sinus Thrombosis Due to Heparin-Induced Thrombocytopenia: A Case Report and Literature Review

Development of cerebral venous sinus thrombosis (CVST) is a rare manifestation of heparin-induced thrombocytopenia (HIT). Herein, we present a case in which heparin administration for primary CVST caused paradoxical worsening of CVST secondary to HIT. A 53-year-old woman diagnosed with CVST was provided with intravenous unfractionated heparin therapy. After 12 days, the patient presented tonic convulsive seizures (TCS). Subsequent magnetic resonance image (MRI) scans revealed an exacerbation of cerebral edema with a subcortical hemorrhage on the left parietal lobe. Laboratory test results revealed a significant decline in platelet count. Heparin was immediately discontinued and replaced with argatroban. The definitive diagnosis of HIT was made through the presence of HIT antibodies. The present case, in which HIT caused the secondary CVST exacerbation, is distinctly rare. Our case provides an instructive example by highlighting the potential of TCS as the first sign of HIT development during CVST treatment.

Being precise with anticoagulation to reduce adverse drug reactions: are we there yet?

Anticoagulants are potent therapeutics widely used in medical and surgical settings, and the amount spent on anticoagulation is rising. Although warfarin remains a widely prescribed oral anticoagulant, prescriptions of direct oral anticoagulants (DOACs) have increased rapidly. Heparin-based parenteral anticoagulants include both unfractionated and low molecular weight heparins (LMWHs). In clinical practice, anticoagulants are generally well tolerated, although interindividual variability in response is apparent. This variability in anticoagulant response can lead to serious incident thrombosis, haemorrhage and off-target adverse reactions such as heparin-induced thrombocytopaenia (HIT). This review seeks to highlight the genetic, environmental and clinical factors associated with variability in anticoagulant response, and review the current evidence base for tailoring the drug, dose, and/or monitoring decisions to identified patient subgroups to improve anticoagulant safety. Areas that would benefit from further research are also identified. Validated variants in VKORC1, CYP2C9 and CYP4F2 constitute biomarkers for differential warfarin response and genotype-informed warfarin dosing has been shown to reduce adverse clinical events. Polymorphisms in CES1 appear relevant to dabigatran exposure but the genetic studies focusing on clinical outcomes such as bleeding are sparse. The influence of body weight on LMWH response merits further attention, as does the relationship between anti-Xa levels and clinical outcomes. Ultimately, safe and effective anticoagulation requires both a deeper parsing of factors contributing to variable response, and further prospective studies to determine optimal therapeutic strategies in identified higher risk subgroups.

Different Types of Vasculitis Complicated by Heparin-Induced Thrombocytopenia-Analysis of Four Cases and Literature Review

Vasculitis and HIT have different etiologies, although both involve autoimmune mechanisms. Treatment of vasculitis often requires the use of an anticoagulant such as heparin, which can lead to the development of HIT and subsequent life-threatening complications. The analysis covered patients hospitalized in the Department of Internal Medicine, Nephrology and Dialysis in the period from September 2020 to March 2023. After analyzing the data, we selected four patients in whom vasculitis treatment was complicated by HIT. These included two patients with ANCA vasculitis and two patients with anti-GBM disease. We also described similar cases reported in the literature.

Laboratory and demographic predictors of functional assay positive status in suspected heparin-induced thrombocytopenia: A multicenter retrospective cohort study

Heparin-induced thrombocytopenia (HIT) is an antibody-mediated immune response against platelet factor 4 (PF4) bound to heparin anticoagulants. A priori identification of patients at-risk for HIT remains elusive and a number of risk factors have been identified, but these associations and their effect sizes have limited validation in large cohorts of suspected HIT patients. The aim of this study was to investigate existing anti-PF4/heparin antibody thresholds and model the relationship of demographic variables and anti-PF4/heparin antibody levels with functional assay positivity across multiple institutions in the absence of detailed clinical data. In a large collection of suspected HIT patients (n = 8904), we tested for associations between laboratory and demographic variables and functional assay positive status as well as anti-PF4/heparin antibody levels. We also tested for correlation between IgG-specific and polyspecific (IgG/IgA/IgM) anti-PF4/heparin antibody values and their ability to predict functional assay positive status using area under the receiver operating characteristic (AUROC). Logistic regression identified increasing anti-PF4/heparin antibody OD levels (OR = 51.84 [37.27-74.34], p < 2.0 × 10-16) and female sex (OR = 1.47 [1.19-1.82], p = 3.5 × 10-4) as risk factors for positive functional assay in the largest cohort with consistent effect sizes in two other cohorts. In a subset of 1175 patients, polyspecific and IgG-specific anti-PF4/heparin antibody values were heterogeneous (mean coefficient of variation = 31.9 %), but strongly correlated (rho = 0.878; p < 2 × 10-16) with similar prediction of functional assay positivity (polyspecific AUROC = 0.976 and IgG-specific AUROC = 0.980). Thus, we recapitulate previously identified risk factors of functional assay positivity, providing precise effect sizes in a large observational population of suspected HIT patients. Our data reinforce the necessity of functional assay confirmation and suggest that, despite heterogeneity, polyspecific and IgG-specific anti-PF4/heparin antibody assays predict functional assay positive status similarly, even in the absence of 4Ts scores and detailed clinical data.

How to approach acute thrombosis and thrombocytopenia

Acute thrombosis and thrombocytopenia pose challenges to the clinician. Thrombocytopenia is naturally viewed as a risk factor for bleeding, and an association with acute thrombosis appears paradoxical. It presents typically as a medical emergency and requires treatment to be started before having confirmatory results. This review supports the attending clinician to recognise and manage conditions that are part of the thrombotic thrombocytopenic syndrome through four illustrative clinical cases. Common themes linking the underlying pathology and treatment are explored to highlight the continued relevance of this rare, but often devastating, presentation.

A Case Report of Native Coronary Artery Thrombosis With Heparin-Induced Thrombocytopenia

Heparin is an anticoagulant which has been widely used in various clinical settings, from thromboprophylaxis to the treatment of thromboembolism. Heparin-induced thrombocytopenia (HIT) is a rare medical condition with severe complications if unrecognised, and it carries significant risks of co-morbidities and mortality. The incidence of HIT is relatively less common in low molecular weight heparin. HIT is more common in the venous system than the arterial circulatory system, and it is rare to see multi-vessel coronary artery thrombosis due to HIT. We hereby report a case of multi-vessel coronary thrombosis secondary to low molecular weight HIT, presenting as a case of ST-segment elevation myocardial infarction. We learned from the case that low molecular weight heparin can cause thrombosis secondary to HIT and HIT could be one of the differential diagnoses in those presenting with ST-elevation myocardial infarct and recent exposure to low molecular weight heparin.

Thrombotic and Thromboembolic Complications After Vaccination Against COVID-19: A Systematic Review

Thromboembolic complications after the COVID-19 vaccination have been reported from all over the world. We aimed to identify the thrombotic and thromboembolic complications that can arise after receiving various types of COVID-19 vaccines, their frequency, and distinguishing characteristics. Articles published in Medline/PubMed, Scopus, EMBASE, Google Scholar, EBSCO, Web of Science, the Cochrane Library, the CDC database, the WHO database, ClinicalTrials.gov, and servers like medRxiv.org and bioRxiv.org, as well as the websites of several reporting authorities between December 1, 2019, and July 29, 2021, were searched. Studies were included if they reported any thromboembolic complications post-COVID-19 vaccination and excluded editorials, systematic reviews, meta-analyses, narrative reviews, and commentaries. Two reviewers independently extracted the data and conducted the quality assessment. Thromboembolic events and associated hemorrhagic complications after various types of COVID-19 vaccines, their frequency, and distinguishing characteristics were assessed. The protocol was registered at PROSPERO (ID-CRD42021257862). There were 59 articles, enrolling 202 patients. We also studied data from two nationwide registries and surveillance. The mean age of presentation was 47 ± 15.5 (mean ± SD) years, and 71.1% of the reported cases were females. The majority of events were with the AstraZeneca vaccine and with the first dose. Of these, 74.8% were venous thromboembolic events, 12.7% were arterial thromboembolic events, and the rest were hemorrhagic complications. The most common reported event was cerebral venous sinus thrombosis (65.8%), followed by pulmonary embolism, splanchnic vein thrombosis, deep vein thrombosis, and ischemic and hemorrhagic stroke. The majority had thrombocytopenia, high D-dimer, and anti-PF4 antibodies. The case fatality rate was 26.5%. In our study, 26/59 of the papers were of fair quality. The data from two nationwide registries and surveillance revealed 6347 venous and arterial thromboembolic events post-COVID-19 vaccinations. COVID-19 vaccinations have been linked to thrombotic and thromboembolic complications. However, the benefits far outweigh the risks. Clinicians should be aware of these complications because they may be fatal and because prompt identification and treatment can prevent fatalities.

In-hospital mortality of heparin-induced thrombocytopenia in end-stage kidney disease. A retrospective national population-based cohort study

AIM

Heparin induced thrombocytopenia (HIT) and end stage kidney disease (ESKD) are independent conditions associated with increased mortality and morbidity, however, whether ESKD is an independent risk factor for increased mortality in HIT admissions is not well studied. Therefore, we aimed to compare in-hospital mortality in HIT admissions based on their ESKD status.

METHODS

This is a retrospective cohort study of HIT hospitalizations aged 18 and older using the 2016-2019 national inpatient sample (NIS) database.

RESULTS

From 2016 to 2019 we had 12 161 admissions for HIT among 28 484 087 total hospitalizations. The annual incidence rate for HIT admissions per 100 000 admissions were: 47, 46, 41.1, and 36.6, respectively (p < .001) in 2016, 2017, 2018, and 2019 respectively. Among HIT admissions, the mean age was 64.3 years, 46.8% were females, 68% were Whites and 16% were Blacks. Black patients have a significantly higher likelihood of in-hospital mortality than White patients (aOR 1.25; 95% CI: 1.06, 1.48; p = .007). Patients who did not have any insurance or self-pay had higher mortality compared to Medicare (aOR 1.64; 95% CI: 1.13, 2.38; p = .009). ESKD status was not associated with higher or lower in-hospital mortality among HIT admissions (aOR 1.002; 95% CI: 0.84, 1.19; p = .981) after adjusting for age, sex, race, and insurance status.

CONCLUSION

There are no higher or lower odds of in-hospital mortality in the ESKD subgroup in HIT admissions in adults. Decreasing incidence of HIT hospitalizations was seen over the years from 2016 to 2019.

Effects of Biological Sex and Pregnancy on SARS-CoV-2 Pathogenesis and Vaccine Outcomes

SARS-CoV-2 is the causative agent of COVID-19 in humans and has resulted in the death of millions of people worldwide. Similar numbers of infections have been documented in males and females; males, however, are more likely than females to be hospitalized, require intensive care unit, or die from COVID-19. The mechanisms that account for this are multi-factorial and are likely to include differential expression of ACE2 and TMPRSS2 molecules that are required for viral entry into hosts cells and sex differences in the immune response, which are due to modulation of cellular functions by sex hormones and differences in chromosomal gene expression. Furthermore, as comorbidities are also associated with poorer outcomes to SARS-CoV-2 infection and several comorbidities are overrepresented in males, these are also likely to contribute to the observed sex differences. Despite their relative better prognosis following infection with SARS-CoV-2, females do have poorer outcomes during pregnancy. This is likely to be due to pregnancy-induced changes in the immune system that adversely affect viral immunity and disruption of the renin-angiotensin system. Importantly, vaccination reduces the severity of disease in males and females, including pregnant females, and there is no evidence that vaccination has any adverse effects on the outcomes of pregnancy.

High-frequency Contactless Sensor for the Detection of Heparin-Induced Thrombocytopenia Antibodies via Platelet Aggregation

Heparin-induced thrombocytopenia (HIT), a severe autoimmune disorder, occurs in patients undergoing heparin therapy. The presence of platelet-activating antibodies against platelet factor 4/Heparin in the blood confirms patients suffering from HIT. The most widely used methods for HIT diagnosis are immunoassays but the results only suit to rule out HIT as the assays provide only around 50% specificity. To confirm HIT, samples with positive results in immunoassays are retested in functional assays (>98% specificity) that track platelet-activating antibodies via platelet aggregation. However, the protocols in functional assays are either time-consuming (due to the requirement of the detection of serotonin release) or require highly trained staff for the visualization of platelets. Here, we applied a cheap and easy-to-use contactless sensor, which employs high-frequency microwaves to detect the changes in the resonant frequency caused by platelet aggregation/activation. Analysis of change in conductivity and permittivity allowed us to distinguish between HIT-like (KKO) and non-HIT-like (RTO) antibodies. KKO caused a stronger reduction of conductivity of platelet samples than RTO. Our results imply that the high-frequency contactless sensor can be a promising approach for the development of a better and easier method for the detection of HIT.

Editor's Choice - Sex Differences in Response to Administration of Heparin During Non-Cardiac Arterial Procedures

OBJECTIVE

Females are more prone to complications during non-cardiac arterial procedures (NCAPs) than males. The current study investigated the difference in the effect of peri-procedural prophylactic heparin in males and females, using the activated clotting time (ACT). This was a retrospective analysis of a prospective multicentre cohort study.

METHODS

All patients undergoing elective NCAP using heparin and ACT measurements between January 2016 and March 2020 were included. Two heparin dosage protocols were used: weight based dosing of 100 IU/kg (international units per kilogram) or a bolus of 5 000 IU. The primary outcome was the anticoagulatory effect of heparin after five minutes, measured by ACT. Secondary outcomes were the effect of heparin after 30 minutes, bleeding complications, and arterial thromboembolic complications (ATECs).

RESULTS

A total of 778 patients were included; 26% were female. After 100 IU/kg (n = 300), females more often reached longer ACT (< 200 seconds: 22% vs. 25%, p = .62; 200 - 250 seconds: 41% vs. 53%, p = .058; 251 - 280 seconds, 26% vs. 15%, p = .030). The mean ACT after 100 IU/kg heparin was 233 seconds (95% confidence interval [CI] 224 - 243) for females and 226 seconds (95% CI 221 - 231) for males (p = .057). After a bolus of 5 000 IU of heparin (n = 411), females reached significantly higher levels of anticoagulation than males (mean ACT 204 seconds vs. 190 seconds: p ≤ .001; ACT < 200 seconds: 44% vs. 66%; p < .001; ACT 200 - 250 seconds: 47% vs. 30%, p = .001; ACT 251 - 280 seconds: 7.8% vs. 2.3%, p = .009). Thirty minutes after heparin administration, 58% of all patients had an ACT < 200 seconds. ATECs did not differ between females and males (6.9% vs. 5.1%, p = .33) but bleeding complications were higher in females (27% vs. 16%, p = .001).

CONCLUSION

Heparin leads to significantly longer ACT in females during NCAP. Further research is needed to investigate whether individually based heparin protocols lead to fewer bleeding complications and lower incidence of ATECs.

A Rare Case of Extensive Cerebral Venous Sinus Thrombosis Complicated by Heparin-Induced Thrombocytopenia

Cerebral venous sinus thrombosis (CVST) is a rare but potentially life-threatening cause of stroke. Several risk factors have been identified including hypercoagulable state, malignancy, use of oral contraceptives, pregnancy, head injury, infection, and prothrombotic states such as heparin-induced thrombocytopenia (HIT). HIT is a prothrombotic state leading to thrombosis in several distinct locations including CVST requiring prompt discontinuation of heparin and initiation of nonheparin anticoagulation to prevent catastrophic consequences. Very rarely, HIT can complicate the ongoing CVST leading to worsening thrombosis and clinical deterioration. We here report an exceedingly rare case of CVST complicated by HIT in a 22-year-old female patient who showed remarkable clinical improvement after discontinuation of heparin and initiation of argatroban.

SARS-CoV-2 Infection, Sex-Related Differences, and a Possible Personalized Treatment Approach with Valproic Acid: A Review

Sex differences identified in the COVID-19 pandemic are necessary to study. It is essential to investigate the efficacy of the drugs in clinical trials for the treatment of COVID-19, and to analyse the sex-related beneficial and adverse effects. The histone deacetylase inhibitor valproic acid (VPA) is a potential drug that could be adapted to prevent the progression and complications of SARS-CoV-2 infection. VPA has a history of research in the treatment of various viral infections. This article reviews the preclinical data, showing that the pharmacological impact of VPA may apply to COVID-19 pathogenetic mechanisms. VPA inhibits SARS-CoV-2 virus entry, suppresses the pro-inflammatory immune cell and cytokine response to infection, and reduces inflammatory tissue and organ damage by mechanisms that may appear to be sex-related. The antithrombotic, antiplatelet, anti-inflammatory, immunomodulatory, glucose- and testosterone-lowering in blood serum effects of VPA suggest that the drug could be promising for therapy of COVID-19. Sex-related differences in the efficacy of VPA treatment may be significant in developing a personalised treatment strategy for COVID-19.

Recognizing Vaccine-Induced Immune Thrombotic Thrombocytopenia

OBJECTIVES

Vaccine-induced immune thrombotic thrombocytopenia is an unexpected consequence of the coronavirus disease 2019 pandemic era. We reviewed the pathogenesis, clinical presentation, diagnosis, and treatment of this rare side effect.

DATA SOURCES

Online search of published medical literature through PubMed, Scopus, Web of Science, and Google Scholar using the terms "COVID-19," "vaccine," "thrombosis" was performed.

STUDY SELECTION

Articles were chosen for inclusion based on their relevance to coronavirus disease 2019, vaccine, and thrombosis.

DATA SYNTHESIS

Vaccine-induced immune thrombotic thrombocytopenia manifests most often as unusual thromboses (cerebral venous sinus thrombosis, splanchnic vein thrombosis) but sometimes also "usual" thromboses (arterial stroke, pulmonary embolism, deep-vein thrombosis), with oftentimes severe thrombocytopenia, that becomes clinically evident 5-30 days after adenovirus-vectored coronavirus disease 2019 vaccine administration. Most patients have disseminated intravascular coagulation. These features are the result of vaccine-triggered formation of anti-platelet factor 4 immunoglobulin G that activate platelets, clinically mimicking autoimmune heparin-induced thrombocytopenia. Early recognition based on thrombosis (sometimes, hemorrhage), thrombocytopenia, and d-dimer elevation within the day 5-30 postvaccine "window" is important given treatment with high-dose IV immunoglobulin plus nonheparin anticoagulation.

CONCLUSIONS

Vaccine-induced immune thrombotic thrombocytopenia is a serious complication of vaccination that is not feasible to anticipate or prevent. When the patient presents with sustained headache, neurologic symptoms/signs, abdominal pain, dyspnea, or limb pain/swelling beginning 5-30 days post vaccination, platelet count and d-dimer must be measured, and imaging for thrombosis performed. Confirmation of vaccine-induced immune thrombotic thrombocytopenia diagnosis should be ordered (platelet factor 4/polyanion enzyme-linked immunosorbent assay; platelet factor 4-enhanced platelet activation testing) as treatment is initiated (nonheparin anticoagulation, IV immunoglobulin).

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.

COVID-19 Vaccine-Associated Thrombosis With Thrombocytopenia Syndrome (TTS): A Systematic Review and Post Hoc Analysis

Background

A new clinical syndrome has been recognized following the COVID-19 vaccine, termed thrombosis with thrombocytopenia syndrome (TTS). The following systematic review focuses on extrapolating thrombotic risk factors, clinical manifestations, and outcomes of patients diagnosed with TTS following the COVID-19 vaccine.

Methods

We utilized the World Health Organization's criteria for a confirmed and probable case of TTS following COVID-19 vaccination and conducted a systematic review and posthoc analysis using the PRISMA 2020 statement. Data analysis was conducted using SPSS V25 for factors associated with mortality, including age, gender, anti-PF4/heparin antibodies, platelet nadir, D-dimer peak, time to event diagnosis, arterial or venous thrombi.

Results

Of the 175 studies identified, a total of 25 studies with 69 patients were included in this systematic review and post hoc analysis. Platelet nadir (P < .001), arterial or venous thrombi (χ2 = 41.911, P = .05), and chronic medical conditions (χ2 = 25.507, P = .041) were statistically associated with death. The ROC curve analysis yielded D-dimer (AUC = .646) and platelet nadir (AUC = .604) as excellent models for death prediction.

Conclusion

Adenoviral COVID-19 vaccines have been shown to trigger TTS, however, reports of patients having received mRNA COVID-19 vaccines are also present. Healthcare providers are recommended to maintain a high degree of suspicion among individuals who have received the COVID-19 vaccine within the last 4 weeks.

Dabigatran Use after Argatroban for Heparin-induced Thrombocytopenia with Thrombosis: A Case Series and Literature Review

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is immune-mediated thrombotic thrombocytopenia following the use of heparin, which contributes to a high limb-amputation rate and mortality if not appropriately handled. There is growing evidence suggesting that novel oral anticoagulants (NOACs) may be effective for treating HIT.

METHODS

We described five rare cases of patients with HIT associated with deep vein thrombosis treated with dabigatran, a member of NOACs. We also reviewed representative cases and literature investigating the use of NOACs to treat patients with HIT to further discuss the efficacy and safety.

RESULTS AND CONCLUSIONS

Following the treatment of dabigatran after argatroban, the platelet count of patients with HIT gradually elevated and reached the normal range eventually. There was no incidence of new symptomatic, objectively-confirmed arteriovenous thromboembolism observed within the 90-day-period follow up. The patient in case 3 presented with gastric bleeding after dabigatran treatment and died in the end. The results suggested that dabigatran use after argatroban may be effective in the treatment of patients with HIT. However, safety should be reconsidered since severe complications were observed in case 3.

Heparin-Induced Thrombocytopenia in Iranian Cardiac Surgery Patients Using the 4Ts Clinical Scoring System and Laboratory Methods

Background: Heparin-induced thrombocytopenia (HIT) is a serious adverse drug reaction. HIT diagnosis needs an algorithmic approach including clinical evaluation and laboratory tests (screening and confirmatory). Few studies have been conducted on HIT in Iran, and most existing research has been general and based on clinical evaluations alone. The present study was conducted to determine the prevalence of HIT among cardiac surgery patients using an algorithmic approach.

Materials and Methods: A cross-sectional study was carried out over a period of 10 months, at Modares Hospital (Tehran, Iran) on 92 patients who were candidates for cardiac surgery. For the clinical evaluation, the 4Ts scoring system was used; in cases with 4Ts scores ≥4, a laboratory evaluation of anti-PF4/heparin antibody (Ab) was performed by enzyme-linked immunosorbent assay (ELISA) and a HIPA test too as a functional confirmatory method. The patients with 4Ts scores ≥4 who were ELISA positive (OD ≥0.2) and HIPA positive were taken as a definite case of HIT.

Results: Of the 92 patients who had undergone cardiac surgery, 14 (15%) had 4Ts scores ≥4. Anti- PF4/heparin Ab was detected in eight patients using the ELISA and in six patients using the HIPA. Ultimately, definite HIT was confirmed in five of the patients.

Conclusion: The prevalence of HIT was 5.4% among the cardiac surgery patients assessed in the present study. To the researchers’ knowledge, this is the first time that HIT has been evaluated in Iran using a comprehensive algorithmic approach including clinical history-taking and both immunological and functional laboratory tests, and the findings showed a slightly higher HIT frequency in this single-center study in comparison with the other studies carried out in other countries.

Incidence, Outcomes and Risk Factors of Heparin-Induced Thrombocytopenia After Total Joint Arthroplasty: A National Inpatient Sample Database Study

Backgrounds: Heparin-induced thrombocytopenia (HIT) is a severe immune-mediated complication of heparin exposure, leading to negative consequences after total hip (THA) and knee arthroplasty (TKA). Materials and Methods: A retrospective study was conducted using the National Inpatient Sample (NIS) database from 2005 to 2014. The incidence and outcomes of HIT after THA or TKA were documented. Logistic regression analysis was performed to identify the postoperative HIT risk factors. Results: A total of 59 3045 patients who underwent THA and 1228 707 patients who underwent TKA were identified. The cumulative incidences were 0.02% and 0.01%, respectively. The HIT group presented significantly higher Charlson Comorbidity Index and Elixhauser Comorbidity Index scores, longer hospital stays (LOS), and higher medical costs. HIT led to a significantly higher mortality rate after THA (2.17% vs 0.16%, P = .0091). In THA, the HIT risk factors were racial minority, AIDS, pulmonary circulation disorders (PCD), psychoses, and hypertension. In TKA, the HIT risk factors were racial minority, PCD, and weight loss. Conclusion: The incidence of HIT after THA and TKA is relatively low; however, HIT significantly increases inpatient mortality, LOS, and medical cost.

Risk Factors in Hospitalized Patients for Heparin-Induced Thrombocytopenia by Real World Database: A New Role for Primary Hypercoagulable States

Background

The aims of the study were to identify predictors of heparin-induced thrombocytopenia (HIT) in hospitalized adults, and to find additional factors associated with higher odds of HIT in primary hypercoagulable states.

Methods

A retrospective matched case-control study using discharge data from National Inpatient Sample database (2012 - 2014) was conducted. In primary outcome analysis, hospitalized patients with and without HIT were included as cases and controls, both matched for age and gender. In secondary outcome analysis, hospitalized patients with primary hypercoagulable states with and without HIT were included as cases and controls, both matched for age and gender. The statistical analyses were performed using Statistical Package for Social Sciences version 25.

Results

There are several predictors of HIT in hospitalized patients, such as obesity, malignancy, diabetes, renal failure, major surgery, congestive heart failure, and autoimmune diseases. In patients with primary hypercoagulable states, the presence of renal failure (odds ratio (OR) 2.955, 95% confidence interval (CI) 1.994 - 4.380), major surgery (OR 1.735, 95% CI 1.275 - 2.361), congestive heart failure (OR 4.497, 95% CI 2.466 - 8.202), or autoimmune diseases (OR 1.712, 95% CI 1.120 - 2.618) further increases the odds of HIT.

Conclusions

In hospitalized patients with primary hypercoagulable states, especially in association with renal failure, major surgery, congestive heart failure, or autoimmune diseases, unfractionated heparin should be used with caution.

Risk of heparinoid use in cosmetics and moisturizers in individuals vaccinated against severe acute respiratory syndrome coronavirus 2

Recently, heparin-induced thrombocytopenia (HIT) after vaccination with the vaccines manufactured by AstraZeneca and Pfizer-BioNTech has been published in the New England Journal of Medicine. These reports state that heparin was not used around the vaccination period in all cases. HIT after vaccination is more common in women; thus, heparinoid use can be suspected to induce HIT.

Early Suspicion of Heparin-Induced Thrombocytopenia for Successful Free Flap Salvage: Reports of Two Cases

Heparin-induced thrombocytopenia (HIT) is an underestimated complication of heparin treatment. Flap loss and related morbidity (even mortality) are caused by occlusion of the capillary vessels by a highly immunogenic complex formed by adherence of antiheparin antibodies to platelet factor 4. Early suspicion and effective treatment of HIT developing in two free flaps are described. We report on the management of two patients with HIT. Both patients were treated successfully by early suspicion and hematology consultation. Heparin products were discontinued; the patients were switched to a nonheparin anticoagulant. We emphasize the importance of early diagnosis, hematologist assessment, and a change to a nonheparin anticoagulant to prevent flap failure and possibly the catastrophic consequences of such failure.

Heparin-Induced Thrombocytopenia After Mitral Valve Replacement

Background: Heparin-induced thrombocytopenia (HIT) is a rare autoimmune reaction that involves a decrease in platelet count following heparin exposure and can be associated with life-threatening thrombosis. Because of their prolonged heparin exposure, patients undergoing cardiac surgery are at risk of HIT, with an incidence of 0.1% to 3%. Case Report: A 65-year-old male with severe mitral regurgitation and preoperative ejection fraction of 20% to 25% underwent mitral valve bioprosthetic replacement with coronary artery bypass graft surgery. Heparin anticoagulation was started on postoperative day (POD) 1. Respiratory failure resulted in prolonged mechanical ventilation and heparinization without the ability to initiate warfarin. While the patient was on heparin, his platelet count declined on POD 2 and then steadily increased to above the preoperative level on POD 7. On POD 10, the patient's platelet count dramatically decreased, and on POD 13 he developed acute common femoral artery occlusion necessitating embolectomy. Intraoperative transesophageal echocardiography revealed heavy thrombus burden across the mitral bioprosthesis. HIT was confirmed with a positive heparin-induced platelet antibody and serotonin release assay. Heparin was stopped and argatroban initiated. The patient underwent reoperative bioprosthetic mitral valve replacement on POD 18 using bivalirudin intraoperatively. Despite resolution of HIT, the patient developed sepsis and died on POD 59. Conclusion: The diagnosis of HIT is challenging in patients who undergo cardiopulmonary bypass. Platelet counts often decrease 40% to 60% during the first 72 hours postoperatively, and the frequency of nonspecific anti-platelet factor 4/heparin antibody formation is high. These findings can mask early signs of HIT and delay diagnosis.

The complicated relationships of heparin-induced thrombocytopenia and platelet factor 4 antibodies with COVID-19

COVID‐19 (coronavirus disease 2019) represents a prothrombotic disorder, and there have been several reports of platelet factor 4/heparin antibodies being present in COVID‐19‐infected patients. This has thus been identified in some publications as representing a high incidence of heparin‐induced thrombocytopenia (HIT), whereas in others, findings have been tempered by general lack of functional reactivity using confirmation assays of serotonin release assay (SRA) or heparin‐induced platelet aggregation (HIPA). Moreover, in at least two publications, data are provided suggesting that antibodies can arise in heparin naïve patients or that platelet activation may not be heparin‐dependent. From this literature, we would conclude that platelet factor 4/heparin antibodies can be observed in COVID‐19‐infected patients, and they may occur at higher incidence than in historical non‐COVID‐19‐infected cohorts. However, the situation is complex, since not all platelet factor 4/heparin antibodies may lead to platelet activation, and not all identified antibodies are heparin‐dependent, such that they do not necessarily reflect “true” HIT. Most recently, a “HIT‐like” syndrome has reported in patients who have been vaccinated against COVID‐19. Accordingly, much more is yet to be learnt about the insidious disease that COVID‐19 represents, including autoimmune outcomes in affected patients.

Heparin-induced thrombocytopenia: pathophysiology, diagnosis and treatment

Introduction: Immune-mediated heparin-induced thrombocytopenia (HIT) is an infrequent complication following heparin exposure but with potentially fatal outcome due to thrombotic complications. Prompt suspension of heparin is necessary if HIT is suspected, followed by initiation of non-heparin anticoagulant therapy.Areas covered: In this review, the pathophysiology and challenges in diagnosing HIT are elucidated. Current and emerging treatment options are discussed with special focus on parenteral thrombin inhibitors (argatroban, bivalirudin), parenteral factor Xa inhibitors (danaparoid, fondaparinux) and direct oral anticoagulants (DOACs [rivaroxaban, apixaban, dabigatran]) including dosing strategies for DOACs. The database PubMed was employed without time boundaries.Expert opinion: Only argatroban holds regulatory approval for HIT treatment in both U.S. and Europe. This treatment is, however, challenged by the need for close monitoring and high costs. Fondaparinux has been increasingly used for off-label treatment and during recent years, evidence for the use of DOACs has emerged. Preliminary results from observational studies hold promise for future use of DOACs in the acute and subacute phase of HIT. However, so far, the use of DOACs in acute HIT should be reserved for clinically stable patients without severe thrombotic complications. Importantly, both fondaparinux and DOAC use is contraindicated in severe renal insufficiency.

Serotonin-release assay-positive but platelet factor 4-dependent enzyme-immunoassay negative: HIT or not HIT?

IgG-specific and polyspecific PF4-dependent enzyme-immunoassays (EIAs) have exceptionally high sensitivity (≥99%) for diagnosis of heparin-induced thrombocytopenia (HIT), a drug reaction caused by platelet-activating antibodies detectable by serotonin-release assay (SRA). The IgG-specific EIAs are recommended for screening, as their high sensitivity is accompanied by relatively high specificity vis-à-vis polyspecific EIAs. We investigated the frequency of SRA-positive/EIA-negative (SRA+/EIA-) HIT, prompted by referral to our reference HIT laboratory of serial blood samples from a patient ("index case") with false-negative IgG-specific EIAs. Despite initial clinical suspicion for HIT, repeat negative IgG-specific EIAs prompted heparin resumption, which triggered recurrent thrombocytopenia and near-fatal cardiac arrest, indicating likely post-heparin HIT-associated anaphylactoid reaction. Further investigations revealed a strong-positive SRA, whether performed with heparin alone, PF4 alone, or PF4/heparin, with inhibition by Fc receptor-blocking monoclonal antibody (indicating IgG-mediated platelet activation); however, five different IgG-specific immunoassays yielded primarily negative (or weak-positive) results. To investigate the frequency of SRA+/EIA- HIT, we reviewed the laboratory and clinical features of patients with this serological profile during a 6-year period in which our reference laboratory investigated for HIT using both SRA and IgG-specific EIA. Although ~0.2% of 8546 patients had an SRA+/EIA- profile, further review of 15 such cases indicated clerical/laboratory misclassification or false-positive SRA in all, with no SRA+/EIA- HIT case identified. We conclude that while SRA+/EIA- HIT is possible-as shown by our index case-this clinical picture is exceptionally uncommon. Moreover, the requirement for a positive EIA is a useful quality control maneuver that reduces risk of reporting a false-positive SRA result.

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.

Thrombosis with Thrombocytopenia Syndrome After Administration of AZD1222 or Ad26.COV2.S Vaccine for COVID-19: A Systematic Review

BACKGROUND

Cases of thrombosis with thrombocytopenia syndrome (TTS) have been reported following vaccination with AZD1222 or Ad26.COV2.S. This review aimed to explore the pathophysiology, epidemiology, diagnosis, management, and prognosis of TTS.

METHODS

A systematic review was conducted to identify evidence on TTS till 4th September 2021. Case reports and series reporting patient-level data were included. Descriptive statistics were reported and compared across patients with different sexes, age groups, vaccines, types of thrombosis, and outcomes.

FINDINGS

Sixty-two studies reporting 160 cases were included from 16 countries. Patients were predominantly females with a median age of 42.50 (22) years. AZD1222 was administered to 140 patients (87·5%). TTS onset occurred in a median of 9 (4) days after vaccination. Venous thrombosis was most common (61.0%). Most patients developed cerebral venous sinus thrombosis (CVST; 66.3%). CVST was significantly more common in female vs male patients (p = 0·001) and in patients aged <45 years vs ≥45 years (p = 0·004). The mortality rate was 36.2%, and patients with suspected TTS, venous thrombosis, CVST, pulmonary embolism, or intraneural complications, patients not managed with non-heparin anticoagulants or IVIG, patients receiving platelet transfusions, and patients requiring intensive care unit admission, mechanical ventilation, or inpatient neurosurgery were more likely to expire than recover.

INTERPRETATION

These findings help to understand the pathophysiology of TTS while also recommending diagnostic and management approaches to improve prognosis in patients.

FUNDING

This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Positive Heparin/PF4 Antibodies and High Mortality Rate: a Retrospective Case-Series Analysis

Introduction

Heparin-induced thrombocytopenia (HIT) is a potentially lethal complication of unfractionated or low-molecular weight heparin therapy. We aimed to determine the incidence and mortality rate of patients with positive heparin/platelet factor 4 (PF4) antibodies, which is a rapid detection test of HIT.

Methods

Coronary artery bypass grafting and mitral and aortic valve surgeries were evaluated. Cardiopulmonary bypass was employed in all patients. The diagnosis of HIT was based on immunological assays. Postoperative complications, mortality rates, and the causes of death were specified in patients with positive heparin/PF4 antibodies.

Results

Postoperative thrombocytopenia was detected in 257 patients. Twenty of these patients undergoing open heart surgery were included in the final analysis. Antibodies against heparin/PF4 complex were positive in 20 patients. The mean body mass index was 28.8±2.3 kg/m², mean value of left ventricular ejection fraction was 48.3±6.7%, cardiopulmonary bypass time was 113.0±35.0 min, aortic cross-clamping time was 88.0±32.7 min, mean intensive care unit length of stay was 10.9±4.9 days, mean preoperative platelet count was 307.250±88528 platelets/microliter, and mean postoperative platelet count was 243.050±89.354 platelets/microliter. The mean duration of heparin exposure was 6.9±2.9 days. The mortality rate was 45% (nine patients) and 1.2% (three patients) in heparin/PF4 complex positive and negative patients, respectively.

Conclusion

Although the incidence of HIT was low in patients undergoing open heart surgery, an increased rate of early mortality was observed in patients with positive heparin/PF4 antibodies.

Prognostic factors for patients with heparin-induced thrombocytopenia: a systematic review

Background  Little is known with regards to the prognostic factors for patients with suspected or diagnosed Heparin-Induced Thromobocytopenia (HIT). The role of patient and therapy characteristics may play a role in predicting the outcome. Aim of the review To investigate the role of patient and therapy characteristics as potential prognostic factors for HIT-related complications (haemorrhagic and thromboembolic events), and mortality. Method The present systematic review was conducted according to the PRISMA statement. In September 2020, the main online databases were accessed: Pubmed, EMBASE, Scopus, Google Scholar. All the clinical trials concerning the management of patients with suspected or confirmed HIT were eligible. Studies evaluating the use of oral anticoagulants (e.g. vitamin K antagonists, Apixaban) were not considered, along with those comparing the use of heparin. For pairwise correlation, the Pearson Product-Moment Correlation Coefficient (r) was used. The final effect was evaluated according to the Cauchy-Schwarz inequality.Results Data from 33 clinical studies (4338 patients) were retrieved. The overall mean age was 62.3 ± 6.6 years old. Patients with HIT-related thromboembolism at the moment of diagnosis were associated with greater rate of haemorrhages (P > 0.0001), thromboembolism (P > 0.0001) and mortality (P = 0.001). Patients with more comorbidities at diagnosis were associated with a greater risk of haemorrhages (P = 0.07), thromboembolism (P = 0.002) and mortality (P = 0.002). Patients with longer duration of the therapy were associated with lower rate of mortality (P = 0.04). ConclusionsPatient comorbidities, presence of HIT-related thromboembolism on admission and shorter anticoagulant therapy were found to be negative prognostic factors. Thrombocythemia on admission, patients age and gender did not influence the overall outcome.

Heparin Induced Thrombocytopenia for the Perioperative and Critical Care Clinician

Purpose of Review

This review will illustrate the importance of heparin-induced thrombocytopenia in the intraoperative and critical care settings.

Recent Findings

Heparin-induced thrombocytopenia (HIT) occurs more frequently in surgical patients compared with medical patients due to the inflammatory release of platelet factor 4 and perioperative heparin exposure. Recognition of this disease requires a high index of suspicion. Diagnostic tools and therapeutic strategies have been expanded and refined in recent years.

Summary

HIT is a condition where antibodies against the heparin/platelet factor 4 complex interact with platelet receptors to promote platelet activation, aggregation, and thrombus formation. Our review will focus on intraoperative and postoperative considerations related to HIT to help the clinician better manage this rare but often devastating hypercoagulable disease process.

Current Perspectives on Diagnostic Assays and Anti-PF4 Antibodies for the Diagnosis of Heparin-Induced Thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a recognized clinical entity in patients receiving unfractionated heparin and low–molecular weight heparin. Currently, diagnosing HIT includes the combination of a physician’s clinical suspicion based on a clinical scoring system and a series of laboratory tests. In the present article, we discuss challenges in suspecting and diagnosing HIT in consideration of the turnaround time of available tests and recent advances in techniques and methodologies of newer immunoassays and functional assays.

COVID-19 versus HIT hypercoagulability

A striking feature of COVID-19 is the high frequency of thrombosis, particularly in patients who require admission to intensive care unit because of respiratory complications (pneumonia/adult respiratory distress syndrome). The spectrum of thrombotic events is wide, including in situ pulmonary thrombosis, deep-vein thrombosis and associated pulmonary embolism, as well as arterial thrombotic events (stroke, myocardial infarction, limb artery thrombosis). Unusual thrombotic events have also been reported, e.g., cerebral venous sinus thrombosis, mesenteric artery and vein thrombosis. Several hematology abnormalities have been observed in COVID-19 patients, including lymphopenia, neutrophilia, thrombocytopenia (usually mild), thrombocytosis, elevated prothrombin time and partial thromboplastin times (the latter abnormality often indicating lupus anticoagulant phenomenon), hyperfibrinogenemia, elevated von Willebrand factor levels, and elevated fibrin d-dimer. Many of these abnormal hematologic parameters—even as early as the time of initial hospital admission—indicate adverse prognosis, including greater frequency of progression to severe respiratory illness and death. Progression to overt disseminated intravascular coagulation in fatal COVID-19 has been reported in some studies, but not observed in others. We compare and contrast COVID-19 hypercoagulability, and associated increased risk of venous and arterial thrombosis, from the perspective of heparin-induced thrombocytopenia (HIT), including the dilemma of providing thromboprophylaxis and treatment recommendations when available data are limited to observational studies. The frequent use of heparin—both low-molecular-weight and unfractionated—in preventing and treating COVID-19 thrombosis, means that vigilance for HIT occurrence is required in this patient population.

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HIT and COVID-19 are associated with a high risk of thrombosis (venous > arterial).

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HIT and COVID-19 both feature coagulation and “pancellular” activation.

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Therapeutic anticoagulation is indicated for HIT, but dosing unknown for COVID-19.

Sex differences in pharmacokinetics predict adverse drug reactions in women

BACKGROUND

Women experience adverse drug reactions, ADRs, nearly twice as often as men, yet the role of sex as a biological factor in the generation of ADRs is poorly understood. Most drugs currently in use were approved based on clinical trials conducted on men, so women may be overmedicated. We determined whether sex differences in drug pharmacokinetics, PKs, predict sex differences in ADRs.

METHODS

Searches of the ISI Web of Science and PubMed databases were conducted with combinations of the terms: drugs, sex or gender, pharmacokinetics, pharmacodynamics, drug safety, drug dose, and adverse drug reaction, which yielded over 5000 articles with considerable overlap. We obtained information from each relevant article on significant sex differences in PK measures, predominantly area under the curve, peak/maximum concentrations, and clearance/elimination rates. ADRs were identified from every relevant article and recorded categorically as female-biased, male-biased, or not sex-biased.

RESULTS

For most of the FDA-approved drugs examined, elevated blood concentrations and longer elimination times were manifested by women, and these PKs were strongly linked to sex differences in ADRs. Of the 86 drugs evaluated, 76 had higher PK values in women; for 59 drugs with clinically identifiable ADRs, sex-biased PKs predicted the direction of sex-biased ADRs in 88% of cases. Ninety-six percent of drugs with female-biased PK values were associated with a higher incidence of ADRs in women than men, but only 29% of male-biased PKs predicted male-biased ADRs. Accessible PK information is available for only a small fraction of all drugs CONCLUSIONS: Sex differences in pharmacokinetics strongly predict sex-specific ADRs for women but not men. This sex difference was not explained by sex differences in body weight. The absence of sex-stratified PK information in public records for hundreds of drugs raises the concern that sex differences in PK values are widespread and of clinical significance. The common practice of prescribing equal drug doses to women and men neglects sex differences in pharmacokinetics and dimorphisms in body weight, risks overmedication of women, and contributes to female-biased adverse drug reactions. We recommend evidence-based dose reductions for women to counteract this sex bias.

Heparin-induced Thrombocytopenia: Pathophysiology, Diagnosis and Management

Heparin-induced thrombocytopenia (HIT), even rare, is a life-threatening, immune-mediated complication of heparin exposure. It is considered the most severe non-bleeding adverse reaction of heparin treatment and one of the most important adverse drug reactions. The pathophysiological basis of HIT results from the formation of an immunocomplex consisting of an auto-antibody against platelet factor 4 (PF4) - heparin complex, which binds to the surface of platelets and monocytes, provoking their activation by cross-linking FcgIIA receptors. Platelets and monocyte activation, leads to the generation of catastrophic arterial and venous thrombosis, with a mortality rate of 20%, without early recognition. The definitive diagnosis of HIT i.e., clinical and laboratory evidence, can not be done at the onset of symptoms because laboratory results may not be available for several days. Thus, the initial approach is to predict the likelihood of HIT, because in highly suspected patients immediate heparin cessation and initiation of alternative anticoagulation treatment are crucial for the prevention of the devastating thrombotic sequelae. Herein, we describe the pathophysiology, the clinical manifestations, the diagnostic approach, and the management of patients with 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.

Incidence and outcomes of heparin-induced thrombocytopenia in solid malignancy: an analysis of the National Inpatient Sample Database

Heparin-induced thrombocytopenia (HIT) is an immune-mediated adverse reaction to heparin products characterized by thrombocytopenia with or without thrombosis. This study aimed to determine the incidence, morbidity, mortality and economic burden of HIT in solid-malignancy-related hospitalizations. We analyzed the National Inpatient Sample Database (NIS), the largest public database of hospital admissions in the United States, from January 2012 to September 2015. The primary outcome of the study was the incidence of HIT. Secondary outcomes included incidence of venous thrombosis (acute deep venous thrombosis and pulmonary embolism), arterial thrombosis (thrombotic stroke, myocardial infarctions and other arterial thromboembolism), mortality associated with HIT, length of stay, total hospital charges and disposition. During the study period, 7 437 049 hospitalizations had an associated diagnosis of solid malignancy. Approximately 0·08% (n = 6225) hospitalizations had a secondary diagnosis of HIT in this population. The standardized incidence of total thrombotic events was higher in the solid malignancy with HIT compared to the solid malignancy without HIT group (24·7% vs. 6·8%, P < 0·001). The standardized mortality rate was 4·8% in solid malignancy with HIT compared to 3·4% in the without HIT group (OR, 1·53; 95% CI, 1·25-1·89; P < 0·001). HIT in solid malignancy is a rare condition but associated with increased morbidity and mortality.

Serotonin-release assay-negative heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a prothrombotic drug reaction caused by platelet-activating anti-platelet factor 4 (PF4)/heparin antibodies. Pathogenic HIT antibodies can be detected by the serotonin-release assay (SRA), a platelet activation test. We have regarded the SRA performed in our medical community ("McMaster" SRA) as having high sensitivity and specificity. Recently, the concept of "SRA-negative HIT" has been proposed for enzyme-immunoassay (EIA)-positive/SRA-negative patients with a HIT-compatible clinical picture, who test positive in a PF4-enhanced platelet activation assay. After identifying an index case of SRA-negative HIT, we estimated the frequency of this condition by performing the "PF4-SRA" (modified SRA using high concentrations of added PF4 rather than heparin) in EIA-positive patients from a cohort study evaluating clinical and laboratory diagnosis of HIT. We defined SRA-negative HIT as patients meeting three criteria: clinical picture compatible with HIT (4Ts ≥ 4 points); EIA-positive (≥1.00 units); and PF4-SRA-positive. Among 430 patients, 35 were EIA-positive/SRA-positive and 27 were EIA-positive/SRA-negative. Among these 27 SRA-negative patients, three were found to have subthreshold levels of platelet-activating antibodies by PF4-SRA, of whom one met clinical criteria for SRA-negative HIT. Thus, based on identifying one patient with SRA-negative HIT within a cohort study that found 35 SRA-positive HIT patients, we estimate the sensitivity of the McMaster SRA for diagnosis of HIT to be 35/36 (97.2%; 95% CI, 85.8-99.9%). Although the McMaster SRA is highly sensitive for HIT, occasional SRA-negative but EIA-positive patients strongly suspected of having HIT can have this diagnosis supported by a PF4-enhanced activation assay such as the PF4-SRA.

Simultaneous Liver-Kidney Transplantation in Patient with a History of Heparin-Induced Thrombocytopenia: A Case Report and Literature Review

Patient: Male, 58

Final Diagnosis: Heparin-induced thrombocytopenia

Symptoms: Liver and kidney failure

Medication: —

Clinical Procedure: Simultaneous liver-kidney transplantation

Specialty: Transplantology

Laboratory diagnosis of heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a clinical-pathological disorder; thus, laboratory testing for the pathogenic platelet-activating antiplatelet factor 4 (PF4)/heparin antibodies is central for diagnosis. The "iceberg" model summarizes the inter-relationship between platelet activation assays and PF4-dependent immunoassays, with platelet-activating antibodies comprising a subset of anti-PF4/heparin antibodies. The platelet serotonin-release assay (SRA), performed by reference laboratories, has high sensitivity and specificity for HIT (~95% each), and is especially suited for detecting highly pathogenic HIT sera containing both heparin-dependent and heparin-independent platelet-activating antibodies; this latter subgroup of antibodies explains "autoimmune HIT" disorders (delayed-onset, persisting, spontaneous, heparin "flush," fondaparinux-associated). Recently, SRA-negative HIT has become recognized, in which serum from some HIT patients contains subthreshold levels of platelet-activating antibodies (by SRA) that become detectable using a PF4-enhanced platelet activation assay. Unusual immunologic features of HIT include early antibody detectability (at onset of platelet count fall) and antibody transience (seroreversion). Widely available PF4-dependent enzyme immunoassays (EIAs) have high sensitivity but poor specificity for HIT, although specificity is enhanced with IgG-specific EIAs and strong positive results; unfortunately, EIA results are usually not available in real time. Automated rapid immunoassays, such as the chemiluminescence immunoassay (CLIA) and latex immunoturbidimetric assay (LIA), facilitate real-time laboratory diagnosis. Recently available likelihood ratio (LR) data for positive (LR+) and negative (LR-) test results allow clinicians to adjust their pretest probabilities for HIT, using Bayesian analysis, into real-time posttest probabilities that are dramatically increased (test positive) or decreased (test negative). Moreover, (semi-)quantitative CLIA- and LIA-positive results (weak, moderate, strong positive) can further refine the posttest probability of HIT.

High-dose intravenous immunoglobulin to treat spontaneous heparin-induced thrombocytopenia syndrome

Essentials Spontaneous HIT syndrome clinically/serologically resembles HIT but without proximate heparin. Rarely, spontaneous HIT syndrome complicates total knee arthroplasty surgery. Mesenteric vein thrombosis is a rare presentation of spontaneous HIT syndrome. IVIg rapidly corrects thrombocytopenia by inhibiting heparin-independent platelet activation. SUMMARY: Spontaneous heparin-induced thrombocytopenia (HIT) syndrome is an autoimmune HIT (aHIT) disorder characterized by thrombocytopenia, thrombosis, and HIT antibodies despite no proximate heparin exposure. For unknown reasons, many cases occur after total knee arthroplasty. A 52-year-old woman presented 12 days posttotal knee replacement (aspirin thromboprophylaxis) with gastrointestinal bleeding (superior mesenteric vein thrombosis); the platelet count was 63 × 109 L-1 . After bowel resection and a brief course of heparin, treatment was changed to argatroban followed by fondaparinux. In addition, high-dose intravenous immunoglobulin (IVIg), 1 g kg-1 on 2 consecutive days, resulted in abrupt platelet count rise from 21 (nadir) pre-IVIg to 137 (post-IVIg), and 2 days later to 200 × 109 L-1 . Heparin-independent serum-induced serotonin-release abruptly decreased from 91% (pre-IVIg) to 14% (post-IVIg); although serotonin-release later rebounded to 49%, the patient's platelet counts remained normal. Our observations support the emerging concept that high-dose IVIg is effective for treating aHIT disorders, including spontaneous HIT syndrome.

Mesenteric Ischemia Caused by Heparin-induced Thrombocytopenia: A Case Report

Deep venous thrombosis (DVT) prophylaxis is the current standard of care in trauma patients. While most of the anticoagulation complications are obvious and can be promptly identified, heparin-induced thrombocytopenia (HIT) requires a high index of suspicion for early diagnosis to prevent a potentially fatal outcome. A 39-year-old female presented to our emergency room after sustaining a gunshot wound to her left flank and pelvis requiring a sigmoid colon and left fallopian tube and ovary resection with colostomy diversion. The patient did well in her early postoperative period; however, her condition rapidly deteriorated after that as a result of mesenteric ischemia caused by heparin-induced thrombocytopenia. After multiple visits to the operating room, the patient ended up with short bowel syndrome, necessitating a referral to a bowel transplant center. Our aim is to increase awareness of this potentially lethal complication with a mortality rate up to 30% of patients.

Fibronectin modulates formation of PF4/heparin complexes and is a potential factor for reducing risk of developing HIT

Heparin-induced thrombocytopenia (HIT) is caused by platelet-activating anti-platelet factor 4 (PF4)/heparin antibodies. Platelet activation assays that use "washed" platelets are more sensitive for detecting HIT antibodies than platelet-rich plasma (PRP)-based assays. Moreover, heparin-exposed patients vary considerably with respect to the risk of PF4/heparin immunization and, among antibody-positive patients, the risk of subsequent "breakthrough" of clinical HIT with manifestation of thrombocytopenia. We used washed platelets and PRP, standard laboratory HIT tests, and physicochemical methods to identify a plasma factor interfering with PF4/heparin complexes and anti-PF4/heparin antibody-platelet interaction, thus explaining differences in functional assays. To investigate a modulating risk for PF4/heparin immunization and breakthrough of HIT, we also tested 89 plasmas from 2 serosurveillance trials. Fibronectin levels were measured in 4 patient groups exhibiting different degrees of heparin-dependent immunization and expression of HIT. The heat-labile plasma protein, fibronectin, inhibited PF4 binding to platelets in a dose-dependent fashion, particularly in washed (vs PRP) systems. Fibronectin also inhibited PF4/heparin binding to platelets, anti-PF4/heparin antibody binding to PF4/heparin complexes, and anti-PF4/heparin antibody-induced platelet activation as a result of PF4/heparin complex disruption. In addition, plasma fibronectin levels increased progressively among the following 4 patient groups: enzyme-linked immunosorbent assay (ELISA)+/serotonin-release assay (SRA)+/HIT+ < ELISA+/SRA+/HIT- ∼ ELISA+/SRA-/HIT- < ELISA-/SRA-/HIT-. Altogether, these findings suggest that fibronectin interferes with PF4/heparin complex formation and anti-PF4/heparin antibody-induced platelet activation. Reduced fibronectin levels in washed platelet assays help to explain the greater sensitivity of washed platelet (vs PRP) assays for HIT. More importantly, lower plasma fibronectin levels could represent a risk factor for PF4/heparin immunization and clinical breakthrough of HIT.

An unusual case of bilateral pulmonary embolism in a patient on dual venous thromboprophylaxis, secondary to heparin induced thrombocytopenia

Heparin Induced thrombocytopenia (HIT) is a rare, immune-mediated complication of heparin, associated with both thrombocytopenia and paradoxical thrombotic events. Initial diagnosis is made clinically when platelet count falls by 30% to <100 × 10⁹cells/l or a > 50% decrease from baseline count in association with heparin therapy. Thromboembolic complications are seen in 50% of the cases. We present a case of acute pulmonary embolism (aPE) in a 65 year old male secondary to HIT while on unfractionated heparin for venous thromboprophylaxis. He was admitted to the hospital for severe acute exacerbation of asthma and was on heparin and venodyne boots for venous thrombo-prophylaxis. His chief presenting complaints improved until day 13, when he had severe pleuritic chest pain with worsening of shortness of breath and was desaturating while breathing ambient air. Computed tomography (CT) of the chest with intravenous contrast revealed aPE involving bilateral upper lobe segmental pulmonary arteries. Given the pattern and timing of thrombocytopenia prior to onset of his symptoms and acute thromboembolism, diagnosis of HIT was made which was later supported by positive platelet factor- ELISA and serotonin release assay (SRA) laboratory testing. Heparin and heparin-related products were promptly discontinued and argatroban was started. Later platelet count increased over 150 × 10³/μL and argatroban was switched to warfarin prior to discharge. As heparin is extensively used, all physicians are required to be attentive of this life threatening complication. Discontinuing heparin while substituting with an alternative anticoagulant such as argatroban may become a life-saving strategy in such a case.