Heparin-induced Thrombocytopenia Positive Patients Research Articles

HIT Diagnosis: A Proposed New Definition for Clinical Research

Introduction: Heparin-induced thrombocytopenia (HIT) is a rarely diagnosed but often suspected complication of heparin therapy. Initial diagnosis is generally made based upon a combination of pretest probability (such as the 4Ts score) and the results of readily available immunoassays. However, confirmation requires the result of a functional assay such as the serotonin release assay (SRA), which is currently considered to be the gold standard. Because the SRA is technically challenging, it is offered only in a few reference laboratories, resulting in a turnaround time of several days to a week. In addition, recent data suggest that the accuracy of the SRA may not be as high as previously thought. Thus, new laboratory assays that are both highly sensitive and specific for HIT antibodies are urgently needed. Here we propose a new set of criteria, independent of the SRA, that may be used to define HIT in the evaluation of novel assays.Methods: We conducted a retrospective cohort study of adult inpatients undergoing laboratory testing for suspicion of acute HIT at the University of Washington Medical center and/or Harborview Medical Center between May 2016 and July 2017. All patients underwent enzyme-linked immunosorbent assay (ELISA) testing for antiPF4/heparin antibodies (IgG-specific Zymutest EIA, Hyphen Biomed). According to institutional policy, those samples with optical density (OD) ≥ 0.300 were reflexively sent to a reference laboratory for SRA testing. Charts were examined by trained reviewers for calculation of the 4Ts score, results of ELISA and SRA testing (when available) and outcomes at 30 days including clinical diagnosis/management of HIT and mortality.Results: We identified 155 patients undergoing evaluation for HIT. Each patient was placed into one of three categories: ‘negative’, ‘indeterminate’, or ‘positive’, based upon a combination of 4Ts score and the optical density (OD) resulting from ELISA testing. Any patient with an OD ≤0.300 was considered to be ‘negative’ regardless of the 4Ts score. Patients with ODs ranging from 0.301-0.999 were defined as ‘negative’ unless the 4Ts score was high (6-8), in which case they were defined as ‘indeterminate’. Patients with an OD of 1.000-1.999 were defined as ‘positive’ if the 4Ts was high (6-8), indeterminate if the 4Ts was intermediate (4-5) and negative if the 4Ts was low (0-3). Patients with an OD ≥2.000 were defined as ‘positive’ unless the 4Ts score was low (0-3) in which case they were defined as ‘indeterminate’. The number of patients that fell into each category as well as the number of subjects with a clinically confirmed diagnosis of HIT are shown in Table 1.The median age of all subjects was 60 and was this was roughly similar across ‘negative’, ‘indeterminate’, and ‘positive’ categories (60, 62, and 66, respectively). Males represented 62% of all subjects and 71% of patients categorized as HIT positive. Seventy percent of all subjects received heparin for venous thromboembolism prophylaxis. Eighty-nine percent of ‘negative’ and 100% of ‘indeterminate’ subjects were exposed to unfractionated heparin (UFH). Six of 7 ‘positive’ patients were exposed to UFH and 1 to low molecular weight heparin (LMWH). All ‘positive’ patients were clinically managed for HIT by stopping all heparin products and/or beginning patients on direct thrombin inhibitor therapy, with 57% mortality within 30 days of ELISA testing. One (0.8%) ‘negative’ and 7 (32%) ‘indeterminate’ patients were clinically managed for HIT. Thirty-day mortality was 25% and 4.5% in ‘negative’ and ‘indeterminate’ groups respectively.Discussion: Our study proposes a framework for the use of clinical pretest probability scores and rapidly available HIT ELISA testing to define HIT in research studies. Such a strategy allows for assessment of accuracy of newly developed assays. The inclusion of an ‘indeterminate’ category adds statistical complexity but is necessary to avoid misclassification of patients who may or may not have true HIT. Mortality in HIT positive patients defined in this manner was high, although small numbers limit definitive conclusions and unfractionated heparin was implicated in most cases of HIT, as has been observed previously. [Display omitted] DisclosuresPadmanabhan:BloodCenter of Wisconsin: Patents & Royalties: A patent application has been filed related to the PF4-dependent P-selectin expression assay (Method of Detecting Platelet- Activating Antibodies That Cause Heparin-Induced Thrombocytopenia/Thrombosis; PCT/US14/62591).; Retham Technologies LLC: Equity Ownership.

Predictive value of scoring tools in determining heparin-induced thrombocytopenia in patients on extracorporeal membrane oxygenation.

There are currently no scoring tools validated for use in predicting heparin-induced thrombocytopenia in patients receiving extracorporeal membrane oxygenation. This study aims to determine the predictive value of the Warkentin 4T score, Lilo-Le Louet score, and the heparin-induced thrombocytopenia expert probability score in detecting heparin-induced thrombocytopenia in patients on extracorporeal membrane oxygenation. This was a single center, retrospective, observational cohort study of patients at Rush University Medical Center. Heparin-induced thrombocytopenia-positive patients were defined as those with an optical density greater than or equal to 0.4, consistent with a positive anti-platelet 4 heparin antibody. Out of 39 patients on extracorporeal membrane oxygenation with suspected heparin-induced thrombocytopenia, six (15.4%) were found to be anti-platelet 4-positive. A heparin-induced thrombocytopenia diagnosis was confirmed by serotonin-release assay in two patients (5.1%). The 4T, heparin-induced thrombocytopenia expert probability, and Lilo-Le Louet scoring tools all demonstrated a low positive predictive value (21.4%, 16.7%, and 6.7%, respectively), with the 4T and heparin-induced thrombocytopenia expert probability scores demonstrating the highest specificity (66.7% and 84.8%, respectively) and lowest sensitivity (50% and 16.7%, respectively). The Lilo-Le Louet score had high sensitivity (100%) and low specificity (12.5%) in post-cardiopulmonary bypass patients. Based on the findings of this study, all three scoring tools have limited utility for predicting heparin-induced thrombocytopenia in patients on extracorporeal membrane oxygenation.

The Risk of Major Bleeding in Patients with Suspected Heparin-Induced Thrombocytopenia (HIT)

Introduction: Without prompt treatment, heparin-induced thrombocytopenia (HIT) is associated with a daily rate of life- and limb-threatening thrombosis of 6.1%. Current recommendations are to empirically treat a patient with an intermediate or high pre-test likelihood of HIT with a non-heparin (alternative) anticoagulant while awaiting HIT laboratory test results. The real-world bleeding rates of empiric treatment with an alternative anticoagulant in patients with suspected HIT have not been well-described. We assessed the rates of major bleeding in a prospective cohort of patients with suspected HIT. Because HIT is generally considered a prothrombotic and not a prohemorrhagic disorder, we hypothesized that major bleeding would be less common in alternative anticoagulant-treated patients with HIT than in treated patients who were ultimately determined not to have HIT.Methods: From June 2012 to January 2015, we enrolled 310 patients with suspected HIT at the Hospital of the University of Pennsylvania and an affiliated community hospital. All patients underwent HIT laboratory testing with a poly-specific PF4/heparin ELISA and in-house serotonin release assay. Patients were adjudicated to be HIT-positive or HIT-negative by an independent adjudication panel of HIT experts based on clinical course and results of HIT laboratory testing. We retrospectively reviewed the electronic health record to assess for the presence of a major bleeding event from the time of suspicion of HIT until hospital discharge or death. Major bleeding events were defined by International Society on Thrombosis and Haemostasis (ISTH) criteria (fall in hemoglobin ≥2 g/dL, transfusion of ≥2 units of packed red blood cells, fatal bleed, bleed occurring in a critical organ and/or requiring a repeat surgical intervention). Secondary outcomes of progressive or new thrombosis following suspicion of HIT testing, in-hospital and 30-day mortality were also assessed. Patients were considered to be treated for suspicion for HIT if they received an alternative anticoagulant following a HIT laboratory test order. The demographics and clinical features of patients defined by adjudicated HIT status were compared using the Wilcoxon test and chi-square tests for continuous and for categorical variables, respectively. The proportion of bleeding and thrombotic events were compared between groups using a chi-square test. All analyses were performed using Stata v14.2.Results:The demographics of our cohort by adjudicated HIT status are displayed in Table 1. 44 patients in the cohort were adjudicated to be HIT-positive and 266 were adjudicated HIT-negative. 42/44 (95.5%) HIT-positive patients and 116 of 266 (43.6%) HIT-negative patients received an alternative anticoagulant.Of those who were empirically treated with an alternative anticoagulant, the median duration of treatment was 3 days (IQR 2-5.5) in HIT-negative patients, compared with 11.5 days (IQR 6-16) in the HIT-positive group (p=0.001). The majority of treated patients received argatroban (88.0% of HIT-positive patients and 76.7% of HIT-negative patients). In those patients who received an alternative anticoagulant, a major bleeding event occurred in 40.9% of HIT positive patients and 44.8% HIT negative patients (p=0.45).The majority of major bleeding events met ISTH criteria based on hemoglobin fall or blood transfusion (Table 2). New or progressive thrombosis following suspicion for HIT was more common in HIT-positive patients (35.7%) than in patients who were HIT-negative and treated (15.5%) or not treated (11.3%) (p=0.001) (Table3).Conclusions:Contrary to our hypothesis, HIT was not protective against bleeding. A similar proportion of HIT-positive patients had ISTH major bleeding compared with HIT-negative patients treated with an alternative anticoagulant. The current paradigm for empiric treatment of patients with suspected HIT may need to be reconsidered in light of our findings of greater than expected bleeding associated with treatment. Limitations of our study include relatively small size, recruitment from a single health system, and predominant use of a single alternative anticoagulant (argatroban). Further studies are needed to determine whether our results apply to other centers and other alternative anticoagulants. [Display omitted] DisclosuresPishko:Novo Nordisk: Research Funding. Cuker:Synergy: Consultancy; Genzyme: Consultancy; Kedrion: Membership on an entity's Board of Directors or advisory committees; Spark Therapeutics: Research Funding.

Systematic review of fondaparinux for heparin‐induced thrombocytopenia: When there are no randomized controlled trials

BackgroundFondaparinux is commonly used for treatment of heparin‐induced thrombocytopenia (HIT) despite lack of approval for this indication. High quality randomized controlled trials of this agent are unlikely to be forthcoming. ObjectivesThe objective of this systematic review is to update the literature on the efficacy and safety of fondaparinux for treatment of confirmed and probable HIT based on the available evidence. MethodsPrimary articles were identified using Web of Science and PubMed database searches for English‐language studies from January 2006 to November 2017. Selected studies enrolled consecutive adult patients who received fondaparinux as the primary anticoagulant to treat acute HIT; confirmed the diagnosis by serological testing with a serotonin‐release assay; heparin‐induced platelet activation assay or enzyme‐linked immunosorbent assay; provided clinical criteria used to define HIT and reported clinically important outcomes. ResultsA total of 9 studies were identified with 154 HIT positive patients. Ten experienced a new thrombotic event while receiving fondaparinux (6.5%, 95% CI, 3.4 to 11.7%) and 26 experienced major bleeding (16.9%, 95% CI, 11.7 to 23.6%). Mortality due to thrombosis or bleeding was reported in 5 patients (3.2%, 95% CI, 1.2 to 7.6%). ConclusionsFondaparinux appears to be an effective and safe anticoagulant for treatment of acute HIT despite the absence of randomized trials. Caution should exercised when using fondaparinux in patients with renal insufficiency.

Platelet Count Trends and Prevalence of Heparin-Induced Thrombocytopenia in a Cohort of Extracorporeal Membrane Oxygenator Patients.

To assess the prevalence of heparin-induced thrombocytopenia and to study platelet count trends potentially suggestive of heparin-induced thrombocytopenia in a population of extracorporeal membrane oxygenator patients. Retrospective cohort study. A total of 926-bed teaching hospital. Extracorporeal membrane oxygenator patients who survived longer than 48 hours from extracorporeal membrane oxygenator initiation between January 1, 2009, and December 31, 2013. None. Demographic and clinical data were collected prospectively on all extracorporeal membrane oxygenator patients. Heparin-induced thrombocytopenia testing results and platelet count variables were obtained from the electronic medical record. We used our institutional algorithm to interpret the results of heparin-induced thrombocytopenia testing. Ninety-six extracorporeal membrane oxygenator patients met the inclusion criteria. Eight patients met the algorithm criteria for heparin-induced thrombocytopenia diagnosis and seven of those had documented thromboembolic event while on extracorporeal membrane oxygenator (prevalence of heparin-induced thrombocytopenia and heparin-induced thrombocytopenia related thrombosis, 8.3 and 7.3, respectively). Heparin-induced thrombocytopenia positive patients were younger; all underwent venoarterial extracorporeal membrane oxygenator; spent more hours on extracorporeal membrane oxygenator; had significantly higher heparin-induced thrombocytopenia enzyme-linked immunosorbent assays optical density; had a higher prevalence of thromboembolic events and reached platelet count nadir later. There was no difference in mortality between heparin-induced thrombocytopenia positive and negative patients. Comparison of platelet count trends revealed that there was no statistically significant difference between the predefined study groups. Prevalence of heparin-induced thrombocytopenia and heparin-induced thrombocytopenia-related thrombosis among extracorporeal membrane oxygenator patients at our institution is relatively high. Using platelet count trends to guide decision to test for heparin-induced thrombocytopenia is not an optimal strategy in extracorporeal membrane oxygenator patients. Without a validated pretest probability clinical score, serosurveillance in a defined high-risk group of extracorporeal membrane oxygenator patients may be needed.

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Introduction: Heparin-induced thrombocytopenia (HIT) is a serious adverse effect of heparin treatment characterized by formation of antibodies to heparin–platelet factor 4 (H–PF4) complexes. Clinically, patients with HIT demonstrate a fall in platelet count of more than fifty percent, occurring 5–10 days after the start of heparin treatment; some also develop HIT related thrombosis (HITT). Cardiopulmonary bypass (CPB) is associated with platelet activation, thrombocytopenia and the release into the plasma of large amounts of PF4, as well as exposure to high doses of unfractionated heparin (UFH). Up to 50% of patients develop antibodies to H–PF4 complexes following CPB. However, less than 3% of those patients develop actual HITT, characterized by a second episode of thrombocytopenia 5-10 days after CPB ("P1 pattern" reported by Pouplard et al.). ECMO is a modified CPB circuit that critically ill patients may be exposed to for days and weeks. The incidence of HIT in patients undergoing ECMO is unknown. Furthermore, clinical scores used to diagnose HIT may not be useful in ECMO patients given the high prevalence and persistence of thrombocytopenia caused by artificial circuit and underlying disease. We sought to determine the incidence of HIT/HITT and platelet patterns potentially suggestive of HIT in a cohort of ECMO patients at our institution Methods: After IRB approval, a prospectively collected data set encompassing all ECMO patients from 2009 to 2012 at our institution was reviewed. To compare platelet trends, we only included patients who survived longer than 48 hours after ECMO initiation. Patients were tested for HIT based on presence of thrombocytopenia and clinical suspicion. Institutional criteria defines patients as "HIT positive" if they meet any of the following serological criteria: HIT ELISA Ab(+)/SRA(+); HIT ELISA Ab(-)/SRA(+); HIT ELISA(+) with optical density (OD)>1. "HIT positive" patients with evidence of thrombosis were considered as having HITT. Patients who didn't meet these criteria, or were not tested due to lack of clinical suspicion, were considered "HIT negative". Daily platelet counts were recorded for 10 days inclusive of day of ECMO initiation. Statistical analysis was done using the Wilcoxon rank sum test and Fisher exact test as appropriate for the data sets. Results: 85 patients underwent ECMO from 2009 to 2012. 68 (80%) patients survived longer than 48 hours after ECMO initiation. Of those, 50 patients(73.5%) were tested for HIT ELISA, SRA or both. 4 patients were deemed "HIT positive" and 3 of those patients had documented thrombo-embolic events (HITT) based on predefined criteria (HIT and HITT incidence in the study group of 5.9% and 4.4% respectively). HIT positive patients were significantly younger (53.1 vs. 37.5 years, p=0.048) and had a trend toward higher average HIT ELISA OD (1.246 vs. 0.258, p=0.056). Only significantly different average platelet count between "HIT negative" and "HIT positive group" was at day 10 (163 vs. 53.7, p=0.024).This difference remained significant when we excluded patients from "HIT negative" group who were not tested for HIT ELISA, SRA or both (127.9 vs. 53.7, p=0.033). No other platelet parameter, such as average highest platelet count, platelet nadir, days to nadir and percentage platelet drop, differed significantly between the groups. However, plots of average daily platelet counts suggests a potentially revealing pattern in "HIT positive" group, where a gradual drop to platelet nadir (post ECMO day 5-6) is followed by a period of persistently depressed platelet counts (days 6-10). Conclusions: Incidence of both HIT and HITT is relatively high in patients who survive ECMO for longer than 48 hours at our institution. Traditional clinical scores for diagnosis of HIT such as "4 Ts", or presence of "P 1" platelet pattern (typical of HIT in cardiac surgery patients) are not useful in ECMO patients. Pattern of depressed platelet counts after nadir may be suggestive of HIT in these patients.

Combination Of 4T's Score and Rapid Gel Centrifugation Assay Excludes HIT In a Prospective Cohort Study

The diagnosis of heparin-Induced thrombocytopenia (HIT) is based on the presence of a compatible clinical picture combined with laboratory evidence of heparin-dependent, platelet-activating IgG antibodies. The 4T's Score is a clinical prediction rule that determines the likelihood that a patient has HIT before laboratory testing is performed. A rapid assay (H/PF4-PaGIA, Diamed, Switzerland) uses gel centrifugation to measure binding of antibodies to antigen-coated polystyrene beads (15 min turnover time). The purpose of this study is to evaluate the clinical utility of a diagnostic strategy which combines the 4T's Score with a H/PF4-PaGIA result to guide management of patients with suspected HIT while awaiting results of the serotonin-release assay (SRA). MethodsProspective cohort study of 538 consecutive adult patients with suspected HIT at 4 Canadian hospitals. Physicians completed a standardized 4T's Score sheet and the H/PF4-PaGIA was performed using fresh plasma in a central lab by technologists blinded to the 4T's Score (frozen plasma was used for 85 patients due to disruptions in worldwide availability of the assay.) The SRA and an in-house IgG anti-PF4/H enzyme-immunoassay (EIA) were performed on all patients by blinded technologists. Serologically-confirmed HIT (“HIT positive”) was defined as >50% serotonin release (mean) at three reaction conditions (0.1 U/mL heparin; 0.3 U/mL heparin; enoxaparin, 0.1 U/ml), as well as inhibition (<20% release or >50% inhibition) at 100 U/mL heparin and in the presence of Fc receptor-blocking monoclonal antibody, and a positive EIA. Thrombotic events, major bleeding events, and mortality were captured at day 30.Recommendations for management of patients while awaiting the SRA: patients with a Low 4T's Score (irrespective of H/PF4-PaGIA result) and patients with an Intermediate 4T's Score and negative H/PF4-PaGIA were to receive low-dose danaparoid or fondaparinux. Therapeutic-dose non-heparin anticoagulation was recommended for all patients with an Intermediate 4T's Score and positive H/PF4-PaGIA and for all patients with a High 4T's Score irrespective of H/PF4-PaGIA result.The primary outcome measure was the frequency of management failures defined as a patient with serologically-confirmed HIT who had one of the following combinations of diagnostic testing (a) Low 4T's Score and negative H/PF4-PaGIA; (b) Low 4T's Score and positive H/PF4-PaGIA or (c) Intermediate 4T's Score and negative H/PF4-PaGIA. Results527 patients with mean age 66.5 yr (sd 15.4) were analyzed; 11 patients with missing diagnostic testing results were excluded. Clinical outcomes of the management of patients according to the diagnostic strategy will be reported separately. Results of diagnostic accuracy of the 4T's Score and H/PF4-PaGIA compared to the SRA are provided below.HIT Negative (i.e., SRA-)HIT Positive (i.e., SRA+)TotalH/PF4-PaGIA -H/PF4 PaGIA +H/PF4 PaGIA indeterminateH/PF4 PaGIA -H/PF4 PaGIA +4T's ScoreLow27833226321Intermediate137161010164High243001542Total439523231527The prevalence of serologically-confirmed HIT in the study population was 6.5%. Two patients with indeterminate SRAs but IgG>1.0 were reported as HIT Positive.A negative H/PF4-PaGIA result reduced the probability of HIT based on the 4T's Score from 2.5% to 0.7% (95% CI: 0.1-2.6%) in the Low group, from 6.1% to 0% (95% CI: 0-2.7%) in the Intermediate group and from 35.7% to 0% (95% CI: 0-14.3%) in the High group. A positive H/PF4-PaGIA result increased the probability of HIT based on the 4T's Score to 15.4% (Low 4T's), 38.5% (intermediate 4T's) and 83.3% (High 4T's).The proportion of management failures was 1.5% (95% CI : 0.7%-3.0%). Of the 8 patients who were identified as management failures, 2 (Low 4T's) had a negative H/PF4-PaGIA. Out of 33 HIT Positive patients, 8 (24.2%) would have been missed based on a Low 4T's Score alone and 2 (6.1%) based on negative H/PF4-PaGIA alone. The combination of a Low or Intermediate 4T's Score and a negative H/PF4-PaGIA result had a negative predictive value for HIT of 99.5% (95% CI: 98.3-99.9). ConclusionsThe proportion of management failures was low (1.5%) and within acceptable limits (95% CI : 0.7%-3.0%). Combining the 4T's Score with the result of H/PF4-PaGIA excludes the diagnosis of HIT in the majority of patients with a Low or Intermediate probability for HIT and raises the likelihood of HIT in patients with a High probability. Disclosures:Linkins:BioRad DiaMed: PaGIA assays purchased at cost for study Other. Bates:BioRad Diamed: provided assays for study at cost Other. Lee:BioRad Diamed: provided assays for study at cost Other. Warkentin:GSK: Research Funding; WL Gore: Consultancy; Immucor GTI Diagnostics: Research Funding; Paringenix: Consultancy; Pfizer Canada: Honoraria; BioRad Diamed: provided assays for study at cost, provided assays for study at cost Other.

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Introduction: Given the multitude of thrombocytopenia etiologies in critically ill patients, the diagnosis of heparin-induced thrombocytopenia (HIT) in the intensive care unit (ICU) is often difficult to make. The purpose of this study is to determine if a modified scoring system impacts diagnostic accuracy. Hypothesis: We hypothesized that a modified 3T (m3T) scoring system, which omits clinical evaluation of other thrombocytopenic etiologies, is as effective for the clinical diagnosis of HIT in the ICU when compared to the 4T score. Methods: This was a retrospective cohort analysis of critically ill adults who had an enzyme-linked immunosorbent assay HIT antibody (ELISA HIT Ab) ordered and were identified as HIT positive (optical density [OD]? 0.40) or HIT negative (OD < 0.40) based on the ELISA HIT Ab. Both 4T and m3T scores were retrospectively calculated for patients and the diagnostic accuracy was compared using paired receiver operating characteristic curves (ROC). The number of HIT positive to HIT negative patients was represented by a 1:3 ratio to detect at least a 10% difference in the areas under the ROC curves (AUC) for the 4T and m3T scores. Results: A total of 1487 adult ICU patients with an ELISA HIT Ab ordered between January 2007 and December 2009 were eligible for study enrollment. Application of either exclusion criteria or random selection yielded a total of 232 patients included for analysis (58 HIT positive patients and 174 HIT negative). The majority patients were admitted into surgical ICUs and were primarily exposed to unfractionated heparin. Patients that were HIT positive had a median OD value of 0.61 (IQR 0.47 – 0.92), whereas the median OD value was 0.07 (IQR 0.05 – 0.11) in HIT negative patients (p < 0.001). The AUC for the 4T and m3T scores were 0.683 (95% confidence interval [CI], 0.604-0.762) and 0.680 (95% CI, 0.600-0.758), respectively (p = 0.065). Conclusions: There was no significant difference between the 4T and m3T scoring systems for the diagnosis of HIT in critically ill patients. Further prospective studies should be conducted to validate the m3T scoring system.

Heparin-Induced Thrombocytopenia Antibody Is More Common in Patients with Active Bacterial Infections

Abstract 4678Heparin mobilizes and binds to platelet factor 4 (PF4), forming a heparin-PF4 complex on the platelet surface. Rarely, IgG antibodies recognize and bind to the immune complex, causing platelet activation and thrombin generation, resulting in heparin induced thrombocytopenia (HIT). There is evidence that PF4 has a role in antibacterial host defense and can concurrently prime the immune system with IgG antibodies that can cross-react with the heparin-PF4 complex (Krauel et al, Blood 2011). In the setting of a bacterial infection, the PF4 molecules interact with the bacterial cell wall and induce antibody production. These antibodies are able to recognize any bacteria coated in PF4, resulting in phagocytosis. In the setting of heparin, this antibody can cross react with the heparin-PF4 complex and result in HIT. In vitro studies suggest that E. coli, S. pneumo, and S. aureus coated in PF4 cross-react with human heparin induced anti-PF4/heparin antibodies.We have collected a database of patients being tested for HIT at our institution and performed a retrospective analysis of the incidence of bacterial infections. We hypothesize that patients who have a bacterial infection will be more likely to develop HIT due to anti-bacterial antibodies that cross-react with the heparin-PF4 complex. We collected culture data from 54 patients with positive HIT antibody by ELISA and 178 patients with negative HIT antibody. The incidence of positive cultures and active infections in described in table 1. In the HIT negative patients, 61/178 (34.3%) had positive cultures, compared to 28/54 (51.9%) in the HIT positive patients (p=0.0198). Given that there is data to support E. coli, S. pneumo, and S. aureus-induced antibody cross-reactivity, we performed a subgroup analysis of the incidence of these specific bacterial infection in HIT positive and negative patients (33.3% versus 19.7%, p=0.0357). There is a statistically significant difference noted in the active infections, subgroup analysis, as well presence of any positive cultures in the HIT positive patients as compared to the HIT negative patients.Table 1Colonized Infections (%)Active Infections (%)E. coli, S. pneumo, S. aureus (%)Any + culture (%)HIT negative (n=178)15 (8.4)61 (34.3)35 (19.7)66 (37.1)HIT positive (n=54)2 (3.7)28 (51.9)18 (33.3)29 (53.7)p value0.2420.01980.03570.0293This data supports that in the setting of active infection, particularly with E. coli, S. pneumo, and S. aureus, HIT antibody results should be carefully evaluated. Patients with positive cultures are likely to have thrombocytopenia from infection or sepsis, regardless of the presence of a HIT antibody. Thus, additional factors, such as the patient's 4T score and the presence of thrombosis should be considered prior to initiating treatment for HIT. Disclosures:No relevant conflicts of interest to declare.

Comparison of Seven Generic Enoxaparins with Lovenox® on In Vitro Cross-Reactivity with Antibodies From Heparin Induced Thrombocytopenia.

AbstractAbstract 1105 Introduction:Heparin induced thrombocytopenia (HIT) is the major complication of heparin treatment but is less frequent in patients treated with low molecular weight heparins (LMWHs) than with unfractionated heparin (UFH). Cross immunological reactions of LMWHs with HIT antibodies from patients treated with UFH is a common finding. The immunological profile is among the criteria for similarity of a generic LMWHs. The cross reactivity of generic LMWHs with HIT antibodies has yet to be compared with the innovator product. Aim:To compare the profile of platelet aggregation induced by HIT antibodies in the presence of Lovenoxâ or seven generic enoxaparins. Methods:Platelet activation by HIT antibodies in the presence of UFH (Héparine Choay, France), branded enoxaparin (Lovenox®) and 7 generics (Novex®, Enoxa®, Dilutol®, Versa®, Cutenox®, Loparin®, Fibrinox®) was assessed by Multiple Electrode Aggregometry (MEA, Multiplate, Dynabyte, Germany) according to previously published assay1. Briefly, whole blood (340 μl) from 5 individual healthy donors was incubated with pooled platelet poor plasma (200 μl) from well characterised HIT positive patients and 40 μl of UFH or Lovenox® or generic enoxaparins yielding a final concentration of 1 anti-Xa IU/ml. Platelet aggregation was recorded over 15 min and the area under the curve (AUC, AU*min) was determined. Results:UFH and branded enoxaparin showed high cross reactivity with HIT antibodies in 4 out of 5 experiments. All of the 7 generic enoxaparins gave also a high positive cross-reactivity but the intensity of platelet aggregation varied. The magnitude of the response was classified as follows: Versa® > Enoxa® > Lovenox® > Novex® > Fibrinox® > Cutenox® > Loparin® > Dilutol®. In one experiment Lovenox® showed border-line cross-reactivity with HIT antibodies. Among generic enoxaparins Versa® showed the same extent of cross reactivity as that of Lovenox®. The other generic enoxaparins did not cross react with HIT antibodies. Conclusions:This is the first study that provides key data on the comparison of in vitro cross reactivity with HIT antibodies of generic enoxaparins versus Lovenox®. In the presence of a cross-reactivity of the originator enoxaparin with heparin-PF4-IgG immune complex, there is also a cross-reactivity of the 7 studied generic enoxaparins. The intensity of cross-reactivity is an additional criterion for comparison of generic LMWHs and the originator one. The differences on the intensity of cross reactivity follow the same pattern in the case of border line cross reactivity of the originator enoxaparin.

A simple measure to reduce the incidence of heparin induced thrombocytopenia (HIT) in cardiac intensive care patients – a retrospective observational analysis

Heparin induced thrombocytopenia (HIT) is an immune-mediated drug reaction associated with the administration of heparin that leads to a reduced platelet count. HIT has an incidence in the general population of around 3% and causes arterial and venous thromboses that are life threatening. The diagnosis of HIT should be considered if the platelet count falls by 50% or more or below the laboratory normal range [1]. The pathophysiology involves development of IgG antibodies that recognise and bind the platelet factor 4/heparin complex resulting in platelet aggregation and thrombus formation. Our unit stopped adding heparin to the pressure transducer flush systems in both theatres and cardiac intensive care unit (CICU) and the aim of this observational study was to audit the effect on the incidence of HIT. All patients with a diagnosis of HIT who tested antibody positive on an enzyme- linked immunosorbent assay (ELISA) for the HIT antibody between 30 January 2006 and 22 March 2007 were identified (Group 1). Following removal of heparin from pressure transducer flush, HIT positive patients were also identified between 23 March 2007 and 23 March 2008 (Group 2) The incidences of HIT were compared between the groups. Twenty-one of 884 patients identified in Group 1 were HIT antibody positive whilst eight of the 802 patients in Group 2 were HIT antibody positive (p < 0.03, Chi squared test). Eleven of the 29 patients from both groups who were HPIA positive died before leaving hospital. Before March 2007, the incidence of HIT on our cardiac unit was 2.6% which is in line with the national incidence. In the year following the removal of heparin from pressure transducer flush systems, our incidence of HIT fell to 1%. This action along with use of the British Society of Haematology 2006 guidelines for the estimation of pre-test probability (the 4 Ts) happened simultaneously and both may have contributed to the decreased incidence [1]. Removing heparin from the flush systems may not only have decreased the incidence of HIT and prevented life-threatening complications but it also less expensive (500 ml saline £0.40 versus 500 ml heparinised saline £3.88). Potentially, it also reduces the number of patients who have prolonged stays in the CICU which would have a less easily quantified cost saving [2]. We thank the Department of Haematology, University Hospital of Wales and Prof J. Hall, Head of Department of Anaesthesia, UHW.

Pronounced Reduction in ADAMTS13 Activity Occurs in Heparin Induced Thrombocytopenia but Is Not Due to IgG ANTI-ADAMTS13.

Although severe deficiency in ADAMTS13 activity (<5%) can result in the development of thrombotic thrombocytopenic purpura (TTP), a less marked reduction in ADAMTS13 occurs in the acute phase reaction of sepsis and DIC, and may promote thrombosis in various disease states. Heparin induced thrombocytopenia (HIT) shares many important similarities with TTP. Both are autoimmune prothrombotic disorders characterised by pathogenic antibodies, marked endothelial cell activation, thrombocytopenia, and the development of thrombosis. ADAMTS13 parameters in HIT have not been well characterised and there is no consensus on the severity of the reduction in ADAMTS13 activity. We hypothesize that a pronounced reduction in ADAMTS13 activity can occur in HIT and investigated potential mechanisms underlying ADAMTS13 depletion. We evaluated ADAMTS13 activity, anti-ADAMTS13 IgG and VWF:Ag in double-spun citrated plasma from 20 patients (median age 64, Male:Female = 14:6). 15 were HIT positive (of whom 10 were cardiothoracic cases) and 5 were suspected HIT thrombocytopenic cases, but HIT negative. HIT antibodies were measured by ELISA (either: PF4 enhanced, GTI Diagnostics; or Asserachrom HPIA, Diagnostica Stago) and platelet aggregation (heparin dependence was demonstrated using a known responder as the platelet donor). ADAMTS13 activity was determined by a modified residual collagen binding assay, and anti-ADAMTS13 IgG by an in-house ELISA using recombinant ADAMTS13-coated microtitre plates. VWF:Ag was measured using an immunoturbidimetric assay (Dade Behring). The median HIT antibody concentration in the 15 HIT cases was 1.57 OD using PF4-enhanced ELISA (range 0.91–2.44), and 143% using HPIA (range 69–181%). The median platelet nadir was 57×109/L (range 6–132×109/L). ADAMTS13 activity (normal range (NR): 66–126%) was reduced in 15/15 (100%) HIT positive patients (median 17%, range 0–55%), but also in 4/5 (80%) HIT negative thrombocytopenic patients (median 31%, range 18–76%). There was no statistically significant difference between these two groups (p=0.12). Furthermore, the ADAMTS13 activity of the 10 cardiothoracic patients was not significantly different from the remaining HIT positive cases. Anti-ADAMTS13 IgG was detected in 3/15 HIT positive patients (with IgG levels of 12%, 28% and 69% [NR <4%]) and 1/5 HIT negative cases (IgG of 21%). VWF:Ag was elevated (>200 iu/dL) in 18/20 with a median VWF:Ag of 297 iu/dL (range 165–606 iu/dL). These observations show that ADAMTS13 activity is often low in HIT patients, and can be markedly reduced in some cases. However, ADAMTS13 IgG autoantibodies were only detected in 3 cases, suggesting that autoantibody production is not the predominant mechanism for reduced ADAMTS13 function. The high VWF:Ag observed in HIT is an acute phase reactant and represents excess ADAMTS13 substrate, which drives the process of VWF proteolysis and causes circulating ADAMTS13 depletion. This may ultimately promote the prothrombotic milieu seen in HIT.

Prediction of Heparin Induced Thrombocytopenia: Validation of an Experience-Based Computer Model.

Background: Diagnosis of heparin-induced thrombocytopenia (HIT) requires certain clinical features along with the detection of platelet activating antibodies induced by heparin interaction with platelet factor 4 (PF4). Although the PF4 enzyme-linked immunoassay (ELISA) is a highly sensitive laboratory test, it is not specific. Adding excess heparin to the sample can confirm a positive PF4 ELISA result when it decreases antibody binding by 50% or more, potentially improving the specificity of the assay. We sought to determine the clinical value of the PF4 ELISA and confirmatory test by developing a predictive algorithm for HIT.Methods: We retrospectively identified 116 patients with positive anti-PF4/heparin antibodies at Duke University Medical Center in 2005. We collected data on all patients to allow for clinical classification as HIT positive or HIT negative. HIT positive patients had at least a 30% decline in platelet count after 4–14 days of heparin exposure, or within 48 hours if recent (within last 100 days) heparin exposure. Anti-PF4/heparin antibody titers were determined by ELISA using a confirmatory step with excess heparin. A multivariate logistic regression model was fitted to the 2005 data, to estimate the relationship between patient characteristics (including age, gender, race, and clinical service), laboratory findings (including peak PF4 titer, confirmatory positive status), and clinical HIT status (HIT positive versus HIT negative). The model was then validated on an independent sample of 97 patients with positive anti-PF4/heparin antibodies retrospectively identified at Duke University Medical Center from January to July of 2006.Results: We found no significant relationship between age, race, or gender and clinical HIT status. In multivariate analysis, the peak PF4 titer and confirmatory positive status were independent predictors of HIT. Figure 1 depicts median, 25th, and 75th percentiles of the predicted probabilities for the HIT-positive and HIT-negative patients in the 2005 training and 2006 test populations. The predictive accuracy on the 2005 training set (c-index 0.783, Somer's Dyx 0.566) was maintained when the algorithm was applied to the independent 2006 test population (c-index 0.799, Somer's Dyx 0.597). Figure 2 depicts the ROC curves for both patient populations.Conclusions: This is the first study to our knowledge that has demonstrated the clinical utility of the Heparin/PF4 ELISA confirmatory test for the diagnosis of HIT. Based upon the PF4 ELISA and confirmatory assays, a predictive computer algorithm can distinguish patients likely to have HIT from those who are not. Accurate predicted probabilities of HIT will enable clinicians to more rapidly initiate appropriate therapy. [Display omitted] [Display omitted]

Bivalirudin anticoagulation for cardiopulmonary bypass in a patient with heparin-induced thrombocytopenia

To describe the perioperative management in a heparin-induced thrombocytopenia (HIT) positive patient who had prosthetic valve endocarditis and an aortic root abscess. The patient underwent high-risk cardiac re-operation with the use of the alternative anticoagulant, bivalirudin. A 62-yr-old patient who underwent stentless tissue aortic valve replacement with a Toronto-SPV valve in 1998, was admitted to hospital with symptoms of stroke. A heparin infusion was started and further investigation revealed positive blood cultures. The patient developed HIT which was confirmed by laboratory tests. Echocardiographic examination performed one month later showed vegetations on the aortic tissue valve and a small aortic root abscess. The patient still tested positively for the presence of HIT antibodies and was treated conservatively with antibiotics. A repeat echocardiographic examination showed progression of the aortic root abscess and it was decided to proceed with urgent redo aortic valve surgery. Anticoagulation for cardiopulmonary bypass (CPB) was achieved with the use of a direct thrombin inhibitor (DTI), bivalirudin. Following an uneventful wean from CPB, hemostasis was achieved within 40 min. The postoperative course was uncomplicated and the patient was discharged from hospital on the seventh postoperative day. Bivalirudin is a DTI, which can be used as an alternative anticoagulant for CPB in HIT positive patients. This case report showed a favourable outcome with bivalirudin for urgent complex redo cardiac surgery requiring CPB.

Heparin-PF4 Antibodies in Heparin Induced Thrombocytopenia: Its Relationship with FcgRIIa Polymorphism

We did the pilot study, in an attempt to determine the prevalence of HIT in Indians and determine its relationship, if any, to FcγRIIa polymorphism, the occurrence of heparin-induced thrombocytopenia (HIT) was investigated in 33 Indian patients undergoing cardiovascular surgery (CVS) who received unfractionated heparin (UFH). Platelet counts were performed prior to the initiation of UFH therapy and 5-16 days, post-therapy. The fall in patients' platelet count >35% of the baseline value or <100,000 mL-1 was considered to be suggestive of HIT syndrome. Heparin-induced platelet aggregation (HIPA), Enzyme Linked Immunosorbant assay (ELISA) and Serotonin Release Assay (SRA) tests were performed in all the patients to detect the antibodies formed against the heparin and platelet factor 4 complex (H-PF4). DNA analysis for FcγRIIa polymorphism was done by allele specific PCR. Thrombocytopenia was found to be present in 10 (30%) patients. Of these, 5 patients were found to be positive by HIPA, ELISA and SRA tests. These 5 patients were considered to have classic HIT syndrome. One of these patients had bleeding while the others were asymptomatic. One of the HIT positive patients was found to be homozygous for FcγRIIaHis/ His polymorphism and others were heterozygous, had one defective allele with single amino acid change (Arg 131 His) at FcγRIIa platelet receptor. Frequency of occurrence of homozygous (FcγRIIaHis/ His) and heterozygous (FcγRIIaArg/ His) polymorphism was higher in patients with HIT (100%) than in the normal population (68%). The prevalence of HIT in the pilot study (15%) was higher than that in the west (5%) but comparable to that from Japan (12%) (14). However, the Occurance of FcγRIIa polymorphism in Indian (68%) was higher than in the east (51%) and comparable to that in the west (78%). Thus it appears that the FcγRIIa polymorphism may have some relation to occurrence of HIT. Higher prevalence of FcγRIIa polymorphism in Indian may predispose to higher prevalence of HIT in India. Thus, it is recommended that, heparin-treated patients should be routinely tested for not only aPTT but also for platelet count, HPF4 antibodies and FcγRIIa polymorphism analysis. From the pilot study, it shows that absence of FcγRIIa receptor polymorphism may suggest low or negligible risk of development of HIT antibodies. However, further studies required with more patients using the same protocol.

Combined Thrombin and Platelet Inhibition Treatment for HIT Patients

SummaryDespite the use of potent anticoagulants such as r-hirudin and argatroban, the morbidity and mortality in heparin-induced thrombocytopenia (HIT) patients remains unacceptable. Data from our in vitro investigations show that thrombin inhibitors do not block platelet activation induced by heparin antibodies and heparin but that GPIIb/IIIa receptor inhibitors do block this process. We have treated four HIT positive patients with a combined therapy of thrombin inhibitor and GPIIb/IIIa receptor inhibitor when treatment with thrombin inhibitor alone failed to alleviate acute thrombosis. Combination therapies included r-hirudin (Refludan®) with tirofiban (Aggrastat®) and argatroban (Novastan®) with abciximab (ReoPro®). A reduced dose of the thrombin inhibitor was used with the standard dose of the anti-platelet drug. In all cases, there was no overt bleeding which required intervention, and all patients exhibited clinical improvement or full recovery. These case studies suggest that treatment of active thrombosis in HIT patients with adjunct GPIIb/IIIa receptor inhibitor therapy may be more effective than thrombin inhibitor treatment alone.