Risk Factor For Heparin-induced Thrombocytopenia Research Articles

Genome-Wide Association Study Identifies Variation in ABO As Risk Factor for Platelet Reactivity in Heparin-Induced Thrombocytopenia

Background: Heparin-induced thrombocytopenia (HIT) is an unpredictable, potentially catastrophic adverse effect of heparin treatment resulting from an immune response to platelet factor 4 (PF4)/heparin complexes. Genome-wide association studies (GWAS) have the potential to identify genetic risk factors and generate insights into biological mechanisms of adverse drug reactions. However, published HIT GWAS are underpowered and do not include confirmation of HIT using functional assays. We aimed to identify genetic associations with HIT using a GWAS approach in two European ancestry populations tested for functional assay and PF4/heparin antibody levels. Methods: We performed a GWAS with positive functional assay as the outcome in a large discovery cohort of patients, including heparin-induced platelet aggregation (HIPA) positive cases (n=1243), antibody positive but functional assay negative controls (n=1091), and antibody negative controls (n=1718). Logistic regressions were adjusted for age, gender, and first two principal components. Significant associations from the discovery cohort (alpha=5.00x10-8) were then investigated in a replication cohort of serotonin-release assay (SRA)-confirmed HIT cases (n=173), antibody positive controls (n=125), and antibody negative controls (n=488). All patients were genotyped with the HumanOmniExpressExome BeadChip, including 9,065,510 variants after imputation and quality control. Genes near significantly associated loci were resequenced. Results: In the discovery cohort, a genome-wide significant association was observed between common variation in the ABO gene and HIPA positive status (rs505922 odds ratio 0.738 [0.668-0.816], p=2.813x10-9). This variant was also significantly associated with SRA-confirmed HIT in the replication cohort (odds ratio 0.392 [0.172-0.891], p=0.025). Meta-analysis indicated strong association of ABO variation with positive functional assay (Figure 1). Sequencing and fine-mapping of the ABO locus indicated this effect was driven by ABO blood groups, with the O blood group being a risk factor for HIT (odds ratio 1.42 [1.25-1.61], p=6.11x10-8). Conclusions: We identify common variation in ABO as a risk factor for platelet reactivity and HIT. Strong association of ABO variation may have important implications for prediction and understanding of HIT pathogenesis. Figure 1 Disclosures No relevant conflicts of interest to declare.

Heparin Induced Thrombocytopenia in Patients with COVID-19

BackgroundThe Coronavirus disease-2019 (COVID-19) is a global pandemic caused by novel coronavirus SARS-CoV-2. Acute respiratory and renal failure as well as systemic coagulopathy are critical aspects of the morbidity and mortality in patients with COVID-19. Heparin Induced Thrombocytopenia (HIT) occurs when IgG antibodies form against platelet factor 4-Heparin complex, resulting in platelet activation and removal, leading to a prothrombotic state. HIT is suspected when there is a platelet count decrease of more than 50% after exposure to heparin, along with hypercoagulability. Clinical Scoring systems like 4T Score (Thrombocytopenia, Timing, Thrombosis, no other cause of Thrombocytopenia) have been developed to assess the pretest probability of HIT. The use of unfractionated heparin, post-orthopedic and post-cardiac surgery state, female gender, and old age are recognized as risk factors for HIT. There is a nine-fold increased risk of developing HIT in patients requiring hemodialysis. ICU patients and patients with VTE without thrombocytopenia are considered to have low pre-test probability for HIT. Studies have shown that only 6% who are investigated serologically for HIT actually have the diagnosis. We conducted this study to assess the incidence and risk factors for HIT in COVID-19 positive patients and its impact on mortality.MethodsA retrospective analysis was performed on all patients who were COVID-19 positive and hospitalized between March 1, 2020 and June 26, 2020 at our institution. Patients with intermediate or high suspicion for HIT, based on 4T score of 4 or higher, underwent IgG-specific platelet factor 4(PF4)-dependent enzyme immune assay (EIA). Washed platelet assays such as serotonin release assay (SRA) and heparin-induced platelet aggregation (HIPA) were used as confirmatory tests in cases with intermediate or low optical density (OD) with EIA. The incidence of HIT, its impact on mortality, and positivity of IgG-specific PF4-EIA in COVID-19 patients were studied, and statistical analysis was done with X2 testing. Subgroup analysis was performed based on demographic factors and risk factors for HIT, including exposure to heparin or low molecular weight heparin (LMWH), history of or cancer, recent orthopedic or cardiac surgery, exposure to renal replacement therapy (RRT), and severity of disease (D-dimer >6 ULN, Acute Kidney Injury, ICU admission, and mechanical ventilation requirement). These factors were analyzed by Fisher’s exact test to determine their impact on mortality. The hospital course for HIT antibody-positive patients was further analyzed to study the impact of COVID-19 related therapy, such as Remdesivir, Tocilizumab, Hydroxychloroquine, Steroids, and anticoagulation after diagnosis of HIT.ResultsWEight out of 1265 hospitalized COVID-19 positive patients tested positive for IgG-specific platelet factor 4(PF4)-dependent enzyme immune assay (EIA+). Incidence of EIA+ in COVID-19 patients was 0.6%, which is significantly higher than in the general population 0.2% (p<.0001, 95% CI 0.25-1.20%). The incidence of thromboembolic events in EIA+ patients was 87.5%, significantly higher than the rate of 10.90% in all COVID-19 patients (p<.0001, CI 41.96- 86.98%). The mortality rate in EIA+ patients was 50%, significantly greater than the mortality rate of 12% in all hospitalized COVID-19 patients (p=.0011, CI 9.46-66.53). Serological confirmation of HIT diagnosis was 37.5% (2 had OD>1, 1 was SRA positive) which is significantly higher than confirmation of HIT in nonCOVID-19 patients 6% (p<.0001, 95% CI 29.57-85.32%). All 3 confirmed HIT patients (100%) had severe disease (3/3 required ICU admission, 2/3 required mechanical ventilation, the one not requiring mechanical ventilation required RRT).ConclusionOur study indicates incidence of HIT is higher in the COVID-19 population. The incidence of positive EIA for patients with intermediate to high 4T scores is also higher in COVID-19 positive patients. This can be attributed to the cytokine storm and severe sepsis seen in critically ill COVID-19 patients. Our study also suggests that development of HIT can contribute to increased risk for thromboembolic events as well as mortality of COVID-19 patients, however, our study is limited due to small sample size. Therefore, prospective studies are needed to analyze the impact of HIT on morbidity, mortality and long-term outcomes in COVID-19 patients.TableDisclosuresNo relevant conflicts of interest to declare.

Autoimmune-Associated Human Leukocyte Antigen (HLA) Alleles As Risk Factors for Heparin-Induced Thrombocytopenia (HIT) Antibodies

Introduction: Heparin-induced thrombocytopenia (HIT) is a complication of heparin exposure wherein antibodies (primarily IgG) specific for heparin/platelet-factor-4 (H/PF4) superstructures lead to platelet activation, consumptive thrombocytopenia, and acquired thrombophilia. The immune response is presumably elicited by exposure of a cryptic antigen when heparin and PF4 are bound. However, neither heparin nor PF4 is a foreign antigen in humans, raising the question whether loss of self-tolerance via aberrant antigen presentation by human leukocyte antigen (HLA) may contribute to the development of H/PF4 antibodies. We present evidence that development of high H/PF4 antibody levels is associated with specific HLA alleles, identification of which may elucidate mechanisms for antibody origin and principles for HIT risk stratification.Methods: We conducted a case-control study of 412 adult inpatients tested for enzyme-linked immunosorbent assay H/PF4 antibodies (Diagnostic Stago Asserachrom HPIA-ELISA) for HIT workup after having received intravenous unfractionated heparin. Positive cases (n=60) were individuals with assay optical density (OD) >1.00 while negative controls (n=352) had OD ≤1.00. DNA extracted from peripheral blood of cases and controls were sequenced at HLA-A, -B, -C, -DRB1, -DQB1, and -DPB1 loci (Illumina). High-resolution HLA typing results were analyzed for association with case/control status by Fisher's exact test.Results: Median (IQR) OD was 0.16 (0.08-0.34) for controls and 1.68 (1.23-2.31) for cases. The highest case OD was 3.00. Several HLA alleles were associated with case/control status (Figure 1). For class I loci, B*15:01 (odds ratio, OR: 3.94; 95%CI: 1.82-8.52), C*07:01 (2.43; 1.37-4.30), B*08:01 (2.05; 1.12-3.75), and B*49:01 (6.12; 1.21-31.08) were risk factors for developing H/PF4 antibodies, while B*07:02 (0.43; 0.20-0.94) was protective. For class II loci, DQB1*02:01 (2.50; 1.40-4.48), DRB1*03:01 (2.46; 1.37-4.40), DRB1*04:04 (2.65; 1.15-6.07), and DQB1*03:02 (1.88; 0.98-3.61) were risk factors. After adjusting for age, gender, race, and multiple comparison, B*15:01, C*07:01, DQB1*02:01, and DRB1*03:01 remained significant risk factors (p <0.05). Linkage disequilibrium was present between B*08:01, C*07:01, DQB1*02:01, and DRB1*03:01.Discussion: We identified several HLA alleles associated with H/PF4 antibody formation, comprised almost entirely of well-known risk alleles for autoimmune disease. DQB1*02:01 (DQ2) and DQB1*03:02 (DQ8) are present in nearly all cases of celiac disease. DRB1*03:01 (DR3), linked with DQ2, is the single HLA allele most frequently associated with autoimmune diseases in the literature. B*08:01 (B8) is part of the “super B8” haplotype overlapping with DR3. B*15:01 (B15) has reported associations with type 1 diabetes, Grave's disease and Addison's disease. B*08:01, C*07:01, DQB1*02:01, and DRB1*03:01 appeared to constitute a distinct risk haplotype, separate from B*15:01 or DQB1*03:02. We also identified a protective allele, B*07:02, which has protective associations with ankylosing spondylitis.Our findings suggest individuals who develop high H/PF4 antibody levels following heparin exposure share HLA haplotypes with individuals who develop auto-antibodies in other contexts, perhaps via shared pathophysiology. A history of autoimmune disease may increase one's pre-test probability for HIT compared to the general population, and merits consideration when HIT is on the differential diagnosis. With additional outcomes research, such history might form a useful adjunct to the “4T” screen. Functional implications of HLA associations with HIT warrant further investigation.Figure 1. Human leukocyte antigen alleles associated with heparin/platelet-factor-4 antibody formation. Shown are histograms of optical density (OD) value, contingency-table counts for cases or controls having or missing an allele, odds ratios (OR) in base-2 logarithmic scale with 95% confidence interval, one-tailed Fisher's exact p-value, and known disease associations for each allele. Red: allele present, blue: allele absent, A: cases having allele, B: cases missing allele, C: controls having allele, D: controls missing allele. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

The effect of obesity on the rate of heparin-induced thrombocytopenia.

: Heparin-induced thrombocytopenia (HIT) occurs in patients receiving heparin-containing products due to the formation of platelet-activating antibodies to heparin and platelet factor 4. Diagnosis includes utilization of a scoring system known as the 4-T score, and HIT laboratory assays. Recently, obesity was identified as a potential factor associated with the development of HIT. The objective of this study was to evaluate the association of HIT with obesity in ICU and general medicine patients. We performed a chart review of adult patients within the Methodist Healthcare System, and included patients who had an ELISA and serotonin release assay laboratory tests reported within same hospital admission in which they also had documented receipt of heparin. Obese patients were compared with nonobese patients (BMI < 30) for the primary outcome of HIT occurrence, and secondary outcomes including rate of thrombosis, 4-T scores, and ELISA optical density values. We also generated a 5-T score by including one additional point for those with a BMI of 30 or more to determine the predictive value of this score in identifying HIT. Obesity was confirmed to be a risk factor for HIT, and the 5-T score model was also predictive of the development of HIT. However, the 5-T score was not statistically more predictive of HIT than the 4-T score. Predicting HIT remains challenging and novel markers of HIT are needed to improve HIT recognition. Although obesity did not improve the 4-T score, it may improve the predictability of other scoring systems, and further investigation is warranted.

Risk factors for heparin-induced thrombocytopenia: Focus on Fcγ receptors.

Fcγ receptors have critical roles in the pathophysiology of heparin-induced thrombocytopenia (HIT), a severe immune-mediated complication of heparin treatment. Activation of platelets, monocytes and neutrophils by platelet-activating anti-PF4/heparin IgG antibodies results in thrombocytopenia, hypercoagulability and thrombosis in susceptible patients, effects that depend on FcγRIIA. In addition, FcγRIIIA receptors probably contribute to clearance of platelets sensitised by HIT immune complexes. FcγRI has also been reported to be involved in monocyte activation by HIT IgG antibodies and synthesis of tissue factor. This review focuses on the role of these FcγRs in HIT pathophysiology, including the potential influence of several gene variations associated with variable risk of HIT and related thrombosis. In particular, the 276P and 326Q alleles of CD148, a protein tyrosine phosphatase that regulates FcγRIIA signalling, are associated with a lower risk of HIT, and platelets from healthy donors expressing these alleles are hyporesponsive to anti-PF4/H antibodies. It was also recently demonstrated that the risk of thrombosis is higher in HIT patients expressing the R isoform of the FcγRIIA H131R polymorphism, with HIT antibodies shown to activate RR platelets more efficiently, mainly explained by an inhibitory effect of normal IgG2, which bound to the FcγRIIA 131H isoform more efficiently. Environmental risk factors probably interact with these gene polymorphisms affecting FcγRs, thereby increasing thrombosis risk in HIT.

Are Myeloproliferative neoplasms a risk factor for Heparin-Induced Thrombocytopenia?

Are Myeloproliferative neoplasms a risk factor for Heparin-Induced Thrombocytopenia?

Abstract 13476: Association of HLA-DRB3*01:01 With Heparin-Induced Thrombocytopenia

Introduction: Variation in the human leukocyte antigen (HLA) region is now used clinically to prevent immune-mediated adverse drug reactions. Heparin-induced thrombocytopenia (HIT) is an unpredictable, life-threatening, immune-mediated reaction to heparin treatment. Previous studies have implicated HLA-DR variants in HIT, but HLA alleles which predispose patients to HIT have not been identified. Hypothesis: Our hypothesis is that sequenced HLA alleles are associated with HIT. Methods: We identified HIT cases and heparin-exposed controls in an electronic medical record coupled to a DNA biobank. Cases were defined based on HIT antibody results, HIT risk scoring (4Ts score), and serotonin release assay results. Controls were matched to cases based on age, gender, and type of heparin exposure (unfractionated versus low molecular weight heparin). We performed high resolution, four-digit HLA sequencing for HLA-A, HLA-B, HLA-C, HLA-DR, HLA-DP, and HLA-DQ using long-read 454 FLX sequencing. We tested association of sequenced HLA alleles using conditional univariate logistic regression in a dominant model. Analysis was restricted to individuals with European ancestry and HLA alleles with a frequency greater than 0.01 (n=101). P values were corrected using a Bonferroni correction for 101 sequenced HLA alleles (alpha=4.95x10 -4 ). Results: We identified 77 HIT cases and 345 matched controls. No statistical differences were observed between cases and controls for baseline characteristics. The HLA-DRB3*01:01 allele was significantly associated with HIT (odds ratio 3.55, p=1.09x10 -4 ). No other alleles showed a significant association with HIT. Conclusions: We implicate the HLA-DRB3*01:01 allele as a risk factor for HIT. This allele represents a biologically plausible candidate for HIT, considering the previous literature implicating HLA-DR variation in HIT, the central role of HLA-DR in T cell-dependent antibody production, and the importance of T cells in HIT pathogenesis. Validation of HLA-DRB3*01:01 as a predictor of HIT pathogenesis would lead to preventive genotyping to reduce the risk of HIT.

Heparin-induced thrombocytopenia in patients undergoing cardiac surgery

To investigate the incidence for heparin-induced thrombocytopenia (HIT) in patients undergoing cardiac surgery and to evaluate the risk factors for the generation of HIT-antibody. A total of 315 patients undergoing cardiac surgery in the Department of Cardiothoracic Surgery, Xiangya Hospital between December, 2013 and July, 2014 were enrolled for this study. Among them, 120, 154 and 41 were for surgery of congenital heart defect, valve and coronary artery bypass graft, respectively. There were 170 male patients and 69 patients were under 18 years old. Platelet counts, HIT-antibody and concentration of platelet factor 4 (PF4) were tested before and after the surgery. Diagnosis of HIT was based on "4Ts" (Pretest Clinical Scoring System). HIT was diagnosed in 11 patients (3.5%, 11/315). And thromboembolic events occurred in 2 of 11 patients with HIT. The positive ratio for HIT-antibody was 36.5% (115/315). The coronary artery disease patients had a higher incidence of HIT than that of either the valve disease or the congenital heart defect (17.1%, 7/41 versus 1.9%, 3/154 or 0.8%, 1/120; P<0.05). The congenital heart defect patients had a higher positive ratio for HIT-antibody than that of both the valve disease and the coronary artery disease. The valve disease patients had a higher positive ratio for HIT-antibody than that of the coronary artery disease (51.7%, 62/120 versus 30.5%, 47/154 versus 14.6%, 6/41; P<0.05). Major postoperative complications occurred more frequently in HIT patients (36.4%, 4/11 versus 10.5%, 32/304; P<0.05). Age was a risk factor for HIT (P=0.030, OR=1.083, 95% CI 1.008-1.163). Cardiopulmonary bypass (CPB) (P=0.037, OR=3.113, 95% CI 1.071-9.050) and age (P<0.001, OR=0.970, 95% CI 0.959-0.982) were risk factors for HIT-antibody. The incidence of HIT is low during cardiac surgery, but HIT is a highly risk factor for the major postoperative complications. More attentions should be paid to these severe complications and the risk factors for HIT.

An algorithm for the identification of heparin-induced thrombocytopenia using a medical information database

Using effective algorithms for extracting relevant drug and patient information from electronic medical information data systems is likely to form an increasingly important aspect of pharmacovigilance. To this end, we aimed to develop and validate a novel algorithm for detecting heparin-induced thrombocytopenia (HIT) using a medical information database (MID) and for identifying possible risk factors for HIT. We developed a new algorithm for detecting HIT based on platelet count at distinct time-points and diagnostic information from patients treated with unfractionated heparin (UFH) from April 2008 through March 2012 at Hospital of Hamamatsu University School of Medicine, Japan. Definitive diagnoses of HIT were made through reviews of the medical records by a skilled haematologist. The performance of the algorithm was assessed using the positive predictive value (PPV). Multivariate logistic regression analysis was used to identify possible risk factors for HIT. This algorithm detected 47 patients with suspected HIT in the source population (n = 2875). Of these, 41 were identified as patients with definitive HIT after review of the medical records. The PPV for the algorithm was 87·2%, and the frequency of definitive HIT was 1·4%. Longer-term treatment (≥4 days) with UFH was identified as a risk factor for HIT, with an odds ratio of 5·38 (95% CI: 2·35-12·32) for definitive HIT. We developed a novel, high-PPV detection algorithm for HIT and identified longer-term treatment with UFH as a risk factor for HIT. Our results support the utility of MIDs for improving pharmacovigilance.

A patient with ‘spontaneous’ heparin-induced thrombocytopenia and thrombosis after undergoing knee replacement

Exogenous heparin exposure is the major risk factor for heparin-induced thrombocytopenia and thrombosis (HITT). To date, only five cases of 'spontaneous' HITT have been reported in the literature. We report the case of a 60-year-old man who developed severe thrombocytopenia (15 000/μl) and bilateral deep venous thromboses 10 days after bilateral knee replacement. There was no evidence of heparin exposure upon review of the patient's preoperative and postoperative medication history. Heparin: platelet factor-4 (PF4) antibodies were positive as was the serotonin release assay. Anticoagulation with argatroban along with prednisone and intravenous immune globulin were administered. Anticoagulation with argatroban was bridged to warfarin once his platelet count reached 100 000/μl, and he was continued on oral prednisone taper. Heparin: PF4 antibodies were negative 3 months after the event. Six months later, Doppler ultrasound revealed deep vein thrombosis. This case represents a third 'spontaneous' episode of HITT in the context of knee replacement surgery without heparin administration. It is unclear whether these cases are a result of exposure to a heparin-like proteoglycan such as chondroitin sulfate during surgery that binds PF4, or whether the perioperative pro-inflammatory milieu is the inciting event. Further consideration of precipitating events in these individuals merits further investigation and may lead to valuable insight into the pathophysiology of heparin-independent PF4-related thrombocytopenia and thrombosis.

The homozygous FcγRIIIa-158V genotype is a risk factor for heparin-induced thrombocytopenia in patients with antibodies to heparin-platelet factor 4 complexes

AbstractWe hypothesized that Fcγ receptor IIIa (FcγRIIIa), a polymorphic receptor for the Fc portion of immunoglobulin G (IgG) other than FcγRIIa, was involved in heparin-induced thrombocytopenia (HIT). FcγRIIa-131 and FcγRIIIa-158 genotypes were determined in 102 patients with definite HIT and in 2 control groups of patients treated by heparin (86 subjects without detectable antibodies [Abs] to heparin-platelet factor 4 [H/PF4], Ab- group; 84 patients with Abs to H/PF4 without HIT, Ab+ group). There were no significant differences in genotype distribution or allele frequencies between the 3 groups for FcγRIIa-131H/R polymorphism. In contrast, FcγRIIIa-158V homozygotes were more frequent in the HIT group than in the Ab+ group (P = .02), a difference that was more pronounced in patients with high levels of anti-H/PF4 Abs (P = .01). Since anti-H/PF4 Abs are mainly IgG1 and IgG3, clearance of sensitized platelets may be increased in patients homozygous for the FcγRIIIa-158V allotype, thus contributing to the development of thrombocytopenia. (Blood. 2004;104:2791-2793)

12 Heparin-induced thrombocytopenia: diagnostic tests and biological mechanisms

The discovery of the role of PF4 in the development and pathogenicity of heparin-dependent antibodies which trigger heparin-induced thrombocytopenia (HIT), a rare but severe adverse effect of heparin therapy, has allowed us to revisit the diagnosis of this complication and the pathological mechanisms involved. In this review, diagnostic tests available for confirmation or prediction of HIT are analysed, and new diagnostic strategies are discussed. Factors involved in the development of the heparin-dependent immune response in some heparin-treated patients are then presented. Lastly, it is hypothesized that the presence of antibodies is a risk factor for HIT. The mechanisms which contribute to the development of complications and the role of additional risk factors, including the patient's clinical state and the type of heparin used, are discussed (Magnani, 1993).