Evaluation of pretest clinical score (4 T's) for the diagnosis of heparin-induced thrombocytopenia in two clinical settings

Evaluation of STic Expert® HIT Kit and Its Comparison with ID-PaGIA™ Test in Suspected Heparin-Induced Thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is an adverse drug reaction caused by heparin. HIT occurs due to IgG antibodies directed against heparin-bound platelet factor 4 (PF4). The aim of this study was to evaluate the STic^® Expert HIT for detection of anti-PF4/heparin antibodies in comparison with ID-PaGIA™ kit. The results were further confirmed by Heparin-induced platelet aggregation test (HIPA). A total of 17 patients with a suspected diagnosis of HIT were enrolled. The 4 T scoring of each case was performed. Testing for HIT was carried out by ID-PaGIA™, STic^® Expert HIT, and HIPA. Testing by STic^® Expert HIT test demonstrated positivity in three cases while testing by ID-PaGIA™ test kit revealed four positive cases. Two of these cases were confirmed as HIT by HIPA. The study suggests that STic^® Expert HIT an equally effective test, in combination with the 4T scoring system for detecting/excluding the diagnosis of HIT. A large number of cases are needed for validation.

Use of Cangrelor as a Bridge to Left Ventricular Assist Device Implantation in a Patient with a Recent Drug-Eluting Stent Who Developed Acute Tirofiban-Related Thrombocytopenia

Current guidelines emphasize the need for at least 6-12 months of oral dual antiplatelet therapy consisting of aspirin and a P2Y12 inhibitor following drug-eluting coronary artery stent implantation. In patients with recently implanted coronary artery stents who require urgent cardiac or noncardiac surgery, the benefits of maintaining oral dual antiplatelet therapy must be carefully weighed against the risks of excessive bleeding, and current practice is largely guided by individual surgeon preferences. When the effects of a second oral antiplatelet agent are undesirable during the perioperative period, the use of a short-acting intravenous antiplatelet agent as "bridge" therapy that can be discontinued shortly before surgery is associated with a reduced occurrence of adverse clinical events in patients with recently implanted coronary stents requiring urgent coronary artery bypass graft surgery. Cangrelor is an intravenous adenosine triphosphate analog P2Y12 receptor antagonist with a short plasma half-life that has been used off label in patients with recent coronary stents as a bridge to invasive procedures with excessive bleeding risk. To our knowledge, this is the first case report to demonstrate the safe and effective use of cangrelor as a bridge to left ventricular assist device implantation in a patient with a recently implanted drug-eluting coronary artery stent who developed acute thrombocytopenia following reexposure to tirofiban, a glycoprotein IIb/IIIa inhibitor.

Scoping Review of Interventions Associated with Cost Avoidance Able to Be Performed in the Intensive Care Unit and Emergency Department

A framework for evaluating pharmacists' impact on cost avoidance in the intensive care unit (ICU) and emergency department (ED) has not been established. This scoping review was registered (CRD42018091217) and conducted to identify, aggregate, and qualitatively describe the highest quality evidence for cost avoidance generated by clinical pharmacists on interventions performed in an ICU or ED. Searches were conducted in PubMed, Scopus, CINAHL, Cochrane Central Register of Controlled Trials, and Cochrane Database of Systematic Reviews from inception until April 2018. The level of evidence (LOE) for each specific category of intervention was evaluated according to the Grading of Recommendations, Assessment, Development and Evaluation evidence-to-decision framework. The risks of bias for articles were evaluated using Newcastle Ottawa and Cochrane Collaboration tools. The values from all interventions were inflated to 2018 U.S. dollars using the consumer price index for medical care. Of the 464 articles initially identified, 371 were excluded and 93 were included. After reviewing references from the articles included, an additional 71 articles were also reviewed. The 38 cost intervention categories were supported by varying LOEs: IA (0 categories), IB (1 category), IIA (4 categories), IIB (0 categories), III (27 categories), and IV (6 categories), and articles mostly displayed low to moderate risks of bias. Pharmacists generate cost avoidance through a variety of interventions in critically and emergently ill patients. The quality of evidence supporting specific cost avoidance values is generally low. Quantification of and factors associated with the cost avoidance generated from pharmacists caring for these patients are of paramount importance.

A computerized scoring system to improve assessment of heparin-induced thrombocytopenia risk

Essentials Current risk scores for heparin-induced thrombocytopenia (HIT) are not computer-friendly. We compared a new computerized risk score with the 4Ts score in a large healthcare system. The computerized risk score agrees with the 4Ts score 85% of the time. The new score could potentially improve HIT diagnosis via incorporation into decision support. SUMMARY: Background (HIT) is an immune-mediated adverse drug event associated with life-threatening thrombotic complications. The 4Ts score is widely used to estimate the risk for HIT and guide diagnostic testing, but it is not easily amenable to computerized clinical decision support (CDS) implementation. Objectives Our main objective was to develop an HIT computerized risk (HIT-CR) scoring system that provides platelet count surveillance for timing and degree of thrombocytopenia to identify those for whom diagnostic testing should be considered. Our secondary objective was to evaluate clinical management and subsequent outcomes in those identified as being at risk for HIT. Methods We retrospectively analyzed data from a stratified sample of 150 inpatients treated with heparin to compare the performance of the HIT-CR scoring system with that of a clinically calculated 4Ts score. We took a 4Ts score of ≥ 4 as the gold standard to determine whether HIT diagnostic testing should be performed. Results The best cutoff point of the HIT-CR score was a score of 3, which yielded 85% raw agreement with the 4Ts score and a kappa of 0.69 (95% confidence interval 0.57-0.81). Ninety per cent of patients with 4Ts score of ≥ 4 failed to undergo conventionally recommended diagnostic testing; 38% of these experienced persistent, unexplained thrombocytopenia, and 4% suffered life-threatening thrombotic complications suggestive of undiagnosed HIT. Conclusion The HIT-CR scoring system is practical for computerized CDS, agrees well with the 4Ts score, and should be prospectively evaluated for its ability to identify patients who should be tested for HIT.

Characterization of platelet factor 4 amino acids that bind pathogenic antibodies in heparin-induced thrombocytopenia

Essentials Many patients produce antibodies but few lead to heparin-induced thrombocytopenia (HIT). Pathogenic epitopes are difficult to identify as HIT antibodies are polyclonal and polyspecific. KKO binding to platelet factor 4 (PF4) depends on 13 amino acids, three of which are newly observed. Five amino acids in PF4 can help distinguish pathogenic from non-pathogenic antibodies. SUMMARY: Background Heparin-induced thrombocytopenia (HIT) is an adverse drug reaction that results in thrombocytopenia and, in some patients, thrombotic complications. HIT is mediated by antibodies that bind to complexes of platelet factor 4 (PF4) and heparin. The antigenic epitopes of these anti-PF4/heparin antibodies have not yet been precisely defined, because of the polyspecific immune response that characterizes HIT. Objectives To identify PF4 amino acids essential for binding pathogenic HIT antibodies. Methods Alanine scanning mutagenesis was utilized to produce 70 single point mutations of PF4. Each PF4 mutant was used in an enzyme immunoassay (EIA) to test their capacity to bind a platelet-activating murine monoclonal anti-PF4/heparin antibody (KKO) and HIT patient sera (n = 9). Results and Conclusions We identified 13 amino acids that were essential for binding KKO because they directly affected either the binding site or the antigenic conformation of PF4. We also identified 10 amino acids that were required for the binding of HIT patient sera and five of these amino acids were required for binding both KKO and the HIT patient sera. The 10 amino acids required for binding HIT sera were further tested to differentiate pathogenic HIT antibodies (platelet activating, n = 45) and non-pathogenic antibodies (EIA-positive but not platelet activating, n = 28). We identified five mutations of PF4 that were recognized to be essential for binding pathogenic HIT antibodies. Using alanine scanning mutagenesis, we characterized possible binding sites of pathogenic HIT antibodies on PF4.

Limited impact of clinician education on reducing inappropriate PF4 testing for heparin-induced thrombocytopenia

A high frequency of PF4-ELISA testing in patients suspected to have heparin-induced thrombocytopenia (HIT) despite low 4T scores has been observed in multiple medical centers. Education of clinicians has been suggested to reduce inappropriate testing. We determined trends of PF4-ELISA testing in our institution after the introduction of a HIT education program for clinicians. A HIT Program was developed that included ongoing education, individual feedback, and continuous clinical audit of PF4-ELISA utilization. To assess the impact of education on PF4-ELISA testing trends, we conducted a prospective cohort review of all adult patients who had a PF4-ELISA ordered over a 3 month period (the last quarter of the academic year). 72 PF4-ELISA tests were ordered during the study period. Prospectively calculated 4T scores by investigators revealed 60 low-risk (83.3%), 9 intermediate-risk (12.5%), and 3 high-risk (4.16%). We observed divergent 4T scores with the ordering clinician calculating a higher 4T score compared to the Hematology Quality Improvement (QI) team. The majority of PF4-ELISA testing was ordered by the intensive care units (ICUs) (n = 32, 44.44%). Our study revealed that the frequency of calculation of 4T scores remains poor with the majority inappropriately performed in the ICU setting, with ordering clinicians calculating higher 4T scores than the Hematology QI team. This suggests that clinician education alone is insufficient. Introducing mandatory 4T score calculation prior to PF4-ELISA testing may not be helpful as ordering clinicians can bypass the restriction through inaccurate 4T score calculation.

Anticoagulation of a Percutaneous Left Ventricular Assist Device Using a Low-Dose Heparin Purge Solution Protocol: A Case Series

Background

Impella CP® is a percutaneous left ventricular assist device that requires a heparin–dextrose purge solution. The manufacturer recommends heparin 50 units/mL, but supratherapeutic anticoagulation has been observed with this concentration.

Objective

The purpose of this evaluation was to observe the efficacy and safety of a low-dose heparin-based purge solution (25 units/mL in dextrose 20%). The primary outcome evaluated percentage of activated clotting times (ACTs) below therapeutic range. Secondary objectives included evaluating the incidence of device thrombosis and rate of heparin-induced thrombocytopenia (HIT). Platelet trends were characterized.

Methods

A single-site retrospective review was conducted for all adults with the Impella CP from January 2015 to December 2017.

Results

A total of 18 patients were included. The percentage of ACT readings within goal of 160 to 200 seconds was 49%, and 38% of readings were subtherapeutic. Per BARC bleeding criteria, 22% (n = 4) patients experienced class IIIa bleeding and 39% (n = 7) experienced class II bleeding. Though 4 (22%) patients were tested for HIT, no patients were positive. Patients showed universal reductions in platelet counts.

Conclusions

The use of a low-dose anticoagulation protocol of heparin 25 units/mL in dextrose 20% as needed warrants further evaluation.

Clotting Catastrophies in the Intensive Care Unit

Clotting catastrophies are rarely encountered challenges in the Intensive Care Unit (ICU) and their presentation and progress maybe devastating and fulminant. Dramatic onset and involvement of multiple vascular beds should alert the clinician to look for these disorders. Outcomes may be improved with rapid diagnosis and prompt institution of specific therapies and interdisciplinary liaison holds the key to success.

Heparin-induced thrombocytopenia during extracorporeal life support: incidence, management and outcomes

Background

Heparin-induced thrombocytopenia (HIT) is a severe antibody-mediated reaction leading to transient prothrombosis. However, its incidence in patients on extracorporeal life support (ECLS) is not well described. The aim of this systematic review was to report the incidence of HIT in patients on ECLS, as well as compare the characteristics and outcomes of HIT in patients undergoing veno-arterial extracorporeal membrane oxygenation (VA-ECMO) and veno-venous ECMO (VV-ECMO).

Methods

An electronic search was performed to identify all studies in the English literature examining outcomes of patients with HIT on ECLS. All identified articles were systematically assessed using specific inclusion and exclusion criteria. Random effects meta-analysis as well as univariate analysis was performed.

Results

Of 309 patients from six retrospective studies undergoing ECLS, 83% were suspected, and 17% were confirmed to have HIT. Due to the sparsity of relevant retrospective data regarding patients with confirmed HIT on ECLS, patient-based data was subsequently collected on 28 patients from case reports and case series. Out of these 28 patients, 53.6% and 46.4% of them underwent VA-ECMO and VV-ECMO, respectively. Patients on VA-ECMO had a lower median platelet count nadir (VA-ECMO: 26.0 vs. VV-ECMO: 45.0 per µL, P=0.012) and were more likely to experience arterial thromboembolism (VA-ECMO: 53.3% vs. VV-ECMO: 0.0%, P=0.007), though there was a trend towards decreased likelihood of experiencing ECLS circuit oxygenator thromboembolism (VA-ECMO: 0.0% vs. VV-ECMO: 30.8%, P=0.075) and thromboembolism necessitating ECLS device or circuit exchange (VA-ECMO: 13.3% vs. VV-ECMO 53.8%, P=0.060). Kaplan-Meier survival plots including time from ECLS initiation reveal no significant differences in survival in patients supported on VA-ECMO as compared to VV-ECMO (P=0.300).

Conclusions

Patients who develop HIT on VA-ECMO are more likely to experience more severe thrombocytopenia and arterial thromboembolism than those on VV-ECMO. Further research in this area and development of standardized protocols for the monitoring, diagnosis and management of HIT in patients on ECLS support are warranted.

Drug-associated thrombocytopenia

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

Anticoagulating patients with high-risk acquired thrombophilias

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

Anticoagulating patients with high-risk acquired thrombophilias

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

Use of argatroban for extracorporeal life support in patients with nonheparin-induced thrombocytopenia: Analysis of 10 consecutive patients

Unfractionated heparin (UFH) is currently the standard anticoagulant used in extracorporeal life support (ECLS). However, severe thrombocytopenia occurs frequently during ECLS use and it may be difficult to determine whether this represents heparin-induced thrombocytopenia (HIT) or not. In this case, UFH cannot be continued. Because a confirmatory laboratory test requires time, argatroban is empirically used if HIT is suspected. However, many patients are not found to have HIT. In non-HIT patients, the effectiveness and safety of argatroban are unclear. Thus, we investigated whether argatroban was safe and useful in patients who were suspected of having HIT and were started on argatroban, but were ultimately found to have non-HIT.We retrospectively reviewed all patients on ECLS who received the anticoagulant argatroban as an alternative to UFH between January 2014 and July 2015. The pretest clinical score (4Ts) was calculated, and a score greater than 4 was considered an indication for argatroban. The target-activated clotting time or activated partial thromboplastin time was 1.5 times the patient's upper normal value. Of 191 patients on ECLS during the study period, 10 (5.2%) were treated with argatroban infusion.No patients were found to have antiplatelet factor 4/heparin antibodies. The average maintenance dose of argatroban was 0.1 μg/kg/min. Platelet counts increased significantly following argatroban administration (P = .02). There were no anticoagulation-related complications such as bleeding or thrombosis.Our results suggest that argatroban is a safe alternative to UFH for patients with non-HIT on ECLS. Argatroban may have a more significant platelet-preserving effect than UFH, regardless of whether HIT is present.

The Appropriateness of Testing Platelet Factor 4/Heparin Antibody in Patients Suspected of Heparin-induced Thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is an adverse reaction to the administration of heparin due to the activation of the platelets by the immunoglobulin G (IgG) antibody-platelet factor 4 (PF4)/heparin immune complex. Since the clinical outcome is uncertain (as it could be associated with significant morbidity and sometimes death), an early diagnosis and appropriate treatment are necessary. The 4Ts pretest clinical scoring system and testing for all anti-PF4/heparin antibodies can markedly improve the diagnosis and prompt adequate treatment. Our study was undertaken to retrospectively evaluate the appropriateness of ordering the PF4 enzyme-linked immunosorbent assay (ELISA) test by using the 4Ts scoring system in a tertiary institution. We examined a database of 118 patients who had the PF4 ELISA test and calculated their 4Ts scores retrospectively. A total of 107 patients were evaluated; 95 patients (88.79%) had a negative PF4 ELISA assay and 12 patients tested positive (11.21%). Only one patient tested weakly positive in the low probability group (negative predictive value 98%). In the intermediate group, six patients were strongly positive (optical density (OD) > 1.0). In this latter group, further confirmatory testing using serotonin release assays (SRAs) could have been done. We also evaluated the setting where the tests were performed and found that the majority of patients (63.55%) were tested in the intensive care unit (ICU) where thrombocytopenia is multifactorial. We concluded that the large majority of patients were not appropriately evaluated prior to testing, which incurred unnecessary expense and patient distress. For the proper identification of patients suspected of HIT who should undergo PF4/heparin antibody testing, further education of the ordering physicians is recommended.

Heparin-induced thrombocytopaenia presenting as acute aortic mural thrombosis

Heparin-induced thrombocytopaenia (HIT) is a life and limb-threatening acquired autoimmune complication of heparin-based treatment, characterised by thrombocytopaenia and thrombosis. We present a case of a 77-year-old female with concomitant metastatic ovarian and breast cancer who presented to our institution with worsening shortness of breath. She had been diagnosed with acute pulmonary embolism 1 month earlier that was treated with therapeutic low molecular weight heparin (LMWH). In view of her worsening symptoms, CT imaging was performed. This demonstrated significant progression of the bilateral pulmonary emboli and new mural thrombosis of the thoracic aorta, despite being compliant with therapeutic anticoagulation. She had also developed thrombocytopaenia since commencing LMWH, which raised the clinical suspicion of HIT syndrome. The HIT pre-test probability score was intermediate and LMWH was immediately discontinued pending further investigation. She was commenced on rivaroxaban, a direct oral anticoagulant, and her platelet count soon recovered. Laboratory testing was strongly positive on both immunological and functional assays, thus confirming a diagnosis of HIT syndrome. A repeat CT scan 3 weeks later showed a reduction in the overall thrombus load. Whilst venous thrombosis is observed in as many as half of patients with HIT, arterial thrombosis is a far less common event. Furthermore, arterial involvement usually affects the distal vessels with significant atherosclerotic burden and typically presents as acute limb ischaemia or ischaemic stroke. Aortic thrombosis, as in this case, is a rare complication of HIT syndrome.

Autoimmune heparin-induced thrombocytopenia of delayed onset: a clinical challenge

BACKGROUND

Heparin-induced thrombocytopenia (HIT) usually appears at 5 to 10 days after initiation of heparin. Autoimmune HIT can arise after discontinuation of heparin treatment (delayed-onset HIT) or without any preceding heparin exposure (spontaneous HIT syndrome).

CASE REPORT

This case presents a course of autoimmune HIT with delayed onset. The patient was hospitalized due to influenza pneumonia and received low-molecular-weight heparin thromboprophylaxis for 9 days. Seven days after discharge, she was readmitted because of a cerebral sinus vein thrombosis and severe thrombocytopenia. Intracranial bleeding and brain infarction caused her death.

DISCUSSION

Autoimmune HIT was confirmed by functional heparin-induced platelet (PLT) activation test. Intracranial bleeding prevented continuous and effective anticoagulation. PLT transfusions were given, although they are generally advised against in HIT patients due to potential risk of thromboembolic events.

CONCLUSION

This case presents that testing PLT-activating antibodies both in the presence and in the absence of current heparin treatment helps to diagnose patients with autoimmune HIT. There is conflicting evidence to refuse PLT transfusion when HIT is complicated with life-threatening bleeding.

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

BACKGROUND

Fondaparinux 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.

OBJECTIVES

The 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.

METHODS

Primary 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.

RESULTS

A 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%).

CONCLUSIONS

Fondaparinux 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.

A novel diagnostic algorithm for heparin-induced thrombocytopenia

INTRODUCTION

While diagnostic algorithm using PF4-heparin enzyme-linked immunosorbent assay (ELISA) optical density (OD), and heparin neutralization assay (HNA), or 4T score have been proposed to replace serotonin-release assay (SRA) for heparin-induced thrombocytopenia (HIT), their performance against SRA is unclear. In this study, we proposed and validated the performance of a new algorithm combining PF4-heparin ELISA optical density (OD), HNA and 4T score against SRA for HIT diagnosis.

METHODS

Heparin neutralization assays were performed on specimens submitted for HIT testing with positive PF4-heparin ELISA from December 2015 to September 2017, which were separated into a "training" and a "validation" data set. 4T scores were calculated for ELISA positive cases.

RESULTS

A total of 123 consecutive unique patient samples had positive PF4-heparin ELISA with also HNA data, SRA data, and 4T scores available. Compared to SRA, a "laboratory criteria" (ELISA OD ≥ 1.4 and HNA ≥ 70%) had a sensitivity of 88% (14/16) and specificity of 91% (42/46), and a "combined criteria" (4T score = 8, or 4T score = 6 or 7 and ELISA OD ≥ 1.0, or 4T score = 4 or 5 and ELISA OD ≥ 2.0) had a sensitivity of 75% (12/16) and specificity of 98% (45/46) in the training data set. Laboratory and combined criteria had 90% (56/62) concordance rate. Importantly, for these concordant cases, the diagnostic specificity is 100% (46/46). Based on the data, a novel diagnostic algorithm combining these 2 criteria was proposed and validated prospectively.

CONCLUSION

A novel algorithm has high diagnostic accuracy and potentially could eliminate the need for SRA testing in at least 90% patients with suspected HIT.

Platelet response to direct thrombin inhibitor or fondaparinux treatment in patients with suspected heparin-induced thrombocytopenia

Making a definitive diagnosis of heparin-induced thrombocytopenia (HIT) can be problematic. A prompt platelet rise following treatment has been proposed as a "post-test" criterion for diagnosis. However, the platelet response following discontinuation of heparin and initiation of a recommended alternative anticoagulant remains largely undefined and unstudied. This study aimed to characterize platelet response to initial treatment in patients with a low, intermediate, or high likelihood of having HIT. This was a multicenter retrospective cohort study. Patients were over 18 years in age, underwent serologic testing for HIT, and received alternative anticoagulation treatment for HIT. Classification of each patient's likelihood of having HIT was based on an empiric, pre-hoc combination of the 4T score and serology results. The primary outcome for this study was a platelet count response after initiation of direct thrombin inhibitor (DTI) or fondaparinux therapy within 48 h. 124 patients were analyzed. The sensitivity and specificity of having an immediate platelet rise of at least 10,000/µL by day 2 after starting treatment among high-likelihood for HIT patients were 0.71 (95% CI 0.55-0.84) and 0.64 (95% CI 0.5-0.76), respectively. The negative predictive value of no platelet rise was 75.5% (95% CI 0.61-0.86). A prompt platelet count rise may be appropriate to consider along with other known criteria for the clinical diagnosis of HIT. The rise should be immediate following discontinuation of heparin and initiation of recommended treatment, with an upward rise within 48 h.

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

BACKGROUND

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

METHODS

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

FINDINGS

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

INTERPRETATION

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

FUNDING

None.

Documented vancomycin-induced severe immune-mediated thrombocytopaenia

A 69-year-old man developed Propionibacterium acnes left knee hardware infection after suffering from an infected ingrown toenail. The hardware was removed and he was treated with intravenous vancomycin. Ten days after initiation of vancomycin, he developed severe thrombocytopaenia, epistaxis and petechiae. Vancomycin was discontinued, and platelets rapidly recovered. Serum vancomycin IgG were positive. Patient completed a 6-week course of ceftriaxone with no further complications.

Prevalence and outcome of heparin-induced thrombocytopenia diagnosed under veno-arterial extracorporeal membrane oxygenation: a retrospective nationwide study

PURPOSE

Thrombocytopenia is a frequent and serious adverse event in patients treated with veno-arterial extracorporeal membrane oxygenation (VA-ECMO) for refractory cardiogenic shock. Similarly to postcardiac surgery patients, heparin-induced thrombocytopenia (HIT) could represent the causative underlying mechanism. However, the epidemiology as well as related mortality regarding HIT and VA-ECMO remains largely unknown. We aimed to define the prevalence and associated 90-day mortality of HIT diagnosed under VA-ECMO.

METHODS

This retrospective study included patients under VA-ECMO from 20 French centers between 2012 and 2016. Selected patients were hospitalized for more than 3 days with high clinical suspicion of HIT and positive anti-PF4/heparin antibodies. Patients were classified according to results of functional tests as having either Confirmed or Excluded HIT.

RESULTS

A total of 5797 patients under VA-ECMO were screened; 39/5797 met the inclusion criteria, with HIT confirmed in 21/5797 patients (0.36% [95% CI] [0.21-0.52]). Fourteen of 39 patients (35.9% [20.8-50.9]) with suspected HIT were ultimately excluded because of negative functional assays. Drug-induced thrombocytopenia tended to be more frequent in Excluded HIT at the time of HIT suspicion (p = 0.073). The platelet course was similar between Confirmed and Excluded HIT (p = 0.65). Mortality rate was 33.3% [13.2-53.5] in Confirmed and 50% [23.8-76.2] in Excluded HIT (p = 0.48).

CONCLUSIONS

Prevalence of HIT among patients under VA-ECMO is extremely low at 0.36% with an associated mortality rate of 33.3%, which appears to be in the same range as that observed in patients treated with VA-ECMO without HIT. In addition, HIT was ultimately ruled out in one-third of patients with clinical suspicion of HIT and positive anti-PF4/heparin antibodies.

High prevalence of heparin induced thrombocytopenia with thrombosis among patients with essential thrombocytemia carrying V617F mutation

Arterial and venous complications are major causes of morbidity and mortality in myeloproliferative neoplasms (MPNs). MPNs patients, frequently receive heparin. Heparin-induced thrombocytopenia (HIT) is a rare but potentially life-threatening complication resulting in a severe acquired thrombophilic condition. We carried out a retrospective analysis to evaluate occurrence of new thrombotic events during heparin therapy in essential thrombocythemia (ET) patients. We studied 108 ET patients on heparin for treatment of previous thrombotic events or in thromboprophilaxis. Fifty-eight of them carried JAK 2 V617F mutation while 50 patients were without V617F mutation. Ten patients, among those with JAK 2 V617F mutation after a median of 10 days from heparin treatment presented a platelet drop, new thrombotic events and in 10/10 cases heparin-related antibodies were found. In the other group, two patients (4%) presented a platelet drop, thrombotic manifestations and heparin related antibodies. Our data show that HIT is more frequent, during heparin treatment, in patients with ET carrying V617F mutation, as compared with patients without mutations (P = 0.029). ET with V617F mutation seems to be associated with higher risk of thrombotic complications during heparin treatment. Monitoring platelet counts very closely during the course of heparin is essential especially in ET patients in which platelet drop may be hidden by constitutional thrombocytosis.

Incidence of heparin-induced thrombocytopenia in lower-extremity free flap reconstruction correlates with the overall surgical population

BACKGROUND

Lower-extremity free flap reconstruction is a growing trend in the management of lower extremity wounds. Heparin-induced thrombocytopenia (HIT) is a significant risk to free flap reconstruction. The purpose of this study was to investigate the incidence of HIT in patients receiving lower-extremity free flap surgery.

METHODS

We conducted a retrospective, single center, IRB approved cohort study in which we reviewed all patients who received lower-extremity free flap surgeries between 2011 and 2016. The 4T and HIT Expert Probability (HEP) scores were calculated to assess the likelihood of HIT.

RESULTS

One hundred patient charts revealed three patients with HIT. One patient was excluded due to a prior diagnosis of HIT. HIT incidence in patients receiving lower-extremity free flaps was between 1% and 3%, which is consistent with the national average. 4T scores indicated that two of three HIT-positive patients had a high probability of HIT (approximately 64%), and one of three HIT-positive patients had an intermediate probability (approximately 14%). HEP scoring indicated that all the three (100%) patients had HIT.

CONCLUSIONS

These data suggest that the incidence of HIT in patients receiving lower-extremity free flaps correlates with the incidence of HIT nationally. The use of available scoring methods and other algorithms, combined with patient history helps to assess the immediate perioperative risks of HIT in the absence of rapid immunologic confirmatory tests. This knowledge can allow for successful free flap salvage or for performance of free flaps in patients with a history of HIT.

A Case of Hyperacute Severe Thrombocytopenia Occurring Less than 24 Hours after Intravenous Tirofiban Infusion

Thrombocytopenia is defined as a condition where the platelet count is below the lower limit of normal (<150 G/L), and it is categorized as mild (100–149 G/L), moderate (50–99 G/L), and severe (<50 G/L). We present here a 79-year-old man who developed severe thrombocytopenia with a platelet count of 6 G/L, less than 24 hours after intravenous tirofiban infusion that was given to the patient during a percutaneous transluminal coronary angioplasty procedure with placement of 3 drug-eluting stents. The patient's baseline platelet count was 233 G/L before the procedure. Based on the timeline of events during hospitalization and laboratory evidence, it was highly likely that the patient's thrombocytopenia was the result of tirofiban-induced immune thrombocytopenia, a type of drug-induced immune thrombocytopenia (DITP) which occurs due to drug-dependent antibody-mediated platelet destruction. Anticoagulant-mediated artefactual pseudothrombocytopenia was ruled out as no platelet clumping was seen on the peripheral blood smears. The treatment of DITP includes discontinuation of the causative drug; monitoring of platelet count recovery; or treatment of severe thrombocytopenia with glucocorticoids, IVIG, or platelet transfusions depending on the clinical presentation. The most likely causative agent of this patient's thrombocytopenia—tirofiban—was discontinued, and the patient did not develop any signs of bleeding during the remainder of his hospital stay. His platelet count gradually improved to 24 G/L, and he was discharged on the sixth hospital day.

The Clinical Utility of the Heparin Neutralization Assay in the Diagnosis of Heparin-Induced Thrombocytopenia

Heparin-induced thrombocytopenia (HIT) remains diagnostically challenging. Immunoassays including PF4/heparin enzyme-linked immunosorbent assay (ELISA) have high sensitivity but low specificity. Whether the heparin neutralization assay (HNA) improves the diagnostic accuracy of the PF4/heparin ELISA for HIT is uncertain. In this study, to assess its clinical utility and evaluate whether it improves the diagnostic accuracy for HIT, we implemented HNA in conjunction with PF4/heparin ELISA over a 1-year period. A total of 1194 patient samples were submitted to the laboratory for testing from December 2015 to November 2016. Heparin neutralization assay alone is a poor predictor for HIT, but it has high negative predictive value (NPV): Cases with %inhibition <70% are always negative for serotonin release assay. It improves the diagnostic positive predictive value (PPV) of ELISA without compromising sensitivity: ELISA optical density (OD) ≥1.4 alone has a sensitivity of 88% (14/16) and a PPV of 61% (14/23); with HNA %inhibition ≥70%, the sensitivity remains 88% (14/16) and PPV is 82% (14/17). 4Ts score correlates with ELISA OD and predicts HIT; the predictive accuracy of 4Ts score is further improved by HNA. Interestingly, HNA %inhibition of <70% correlates with low 4Ts scores. Based on its high NPV, HNA has the potential to facilitate more timely and accurate HIT diagnosis.

Heparin-induced thrombocytopenia (HIT): Identification and treatment pathways

Heparin-induced thrombocytopenia (HIT) is a major health problem, especially in cardiac surgery theaters, cardiac catheterization labs, and intensive care units. Some patients with HIT develop serious thrombotic complications like limb ischemia and gangrene, while others may not develop such complications and have only mild thrombocytopenia. Current laboratory diagnostic tools incur significant time delays before confirming HIT, therefore upon clinical suspicion, treatment of HIT should start immediately while awaiting laboratory results. This is a review of the types, phases, pathophysiology, clinical presentation and diagnosis of HIT, and its current management strategies.

Evaluation of Thrombocytopenia in Critically Ill Patients Receiving Continuous Renal Replacement Therapy

BACKGROUND

Continuous renal replacement therapy (CRRT) may be associated with thrombocytopenia in critically ill patients. A confounding factor is concomitant use of unfractionated heparin (UFH) and suspicion for heparin-induced thrombocytopenia (HIT).

OBJECTIVE

To determine the impact of CRRT on platelet count and development of thrombocytopenia.

METHODS

Retrospective analyses evaluated the intrapatient change in platelet count following CRRT initiation. Critically ill adult patients who received CRRT for at least 48 hours were included. The primary outcome was intrapatient change in platelet count from CRRT initiation through the first 5 days of therapy. Secondary outcomes included thrombocytopenia incidence, identification of concomitant factors associated with thrombocytopenia, and frequency of HIT.

RESULTS

80 patients were included. Median platelet count at CRRT initiation (D0) was 128000/µL (81500-212500/µL), which was higher than those on subsequent post-CRRT days (D1: 104500/µL [63000-166750/µL]; D2: 88500/µL [53500-136750/µL]; D3: 91000/µL [49000-138000/µL]; D4: 93000/µL [46000-134000/µL]; and D5: 76000/µL [45500-151000/µL]; P < 0.05 for all). Twenty-five (35%) patients had thrombocytopenia on CRRT D0 compared with D2 (56.3%), D3 (58.7%), and D5 (59.1%); P < 0.05 for all. Controlling for potential confounders, Sequential Organ Failure Assessment score at the time of CRRT initiation was the only independent factor associated with thrombocytopenia. One (1.3%) patient had confirmed HIT. Conclusion and Relevance: This study is the first to demonstrate serial decreases in platelet count across multiple days after CRRT initiation. These data may provide additional insight to thrombocytopenia development in critically ill patients receiving heparin while on CRRT that is not associated with HIT.

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.

Derivation and validation of a practical Bedside Score for the diagnosis of cholecystitis

OBJECTIVE

We sought to develop a practical Bedside Score for the diagnosis of cholecystitis and test its accuracy against the Tokyo Guidelines (TG13).

METHODS

We conducted a retrospective study of 438 patients undergoing urban, academic Emergency Department (ED) evaluation of RUQ pain. Symptoms, physical signs, ultrasound signs, and labs were scoring system candidates. A random split-sample approach was used to develop and validate a new clinical score. Multivariable regression analysis using development data was conducted to identify predictors of cholecystitis. Cutoff values were chosen to ensure positive/negative predictive values (PPV, NPV) of at least 0.95. The score was externally validated in 80 patients at a different hospital undergoing RUQ pain evaluation.

RESULTS

230 patients (53%) had cholecystitis. Five variables predicted cholecystitis and were included in the scores: gallstones, gallbladder thickening, clinical or ultrasonographic Murphy's sign, RUQ tenderness, and post-prandial symptoms. A clinical prediction score was developed. When dichotomized at 4, overall accuracy for acute cholecystitis was 90% for the development cohort, 82% and 86% for the internal and external validation cohorts; TG13 accuracy was 62%-79%.

CONCLUSIONS

A clinical prediction score for cholecystitis demonstrates accuracy equivalent to TG13. Use of this score may streamline work-up by decreasing the need for comprehensive ultrasound evaluation and CRP measurement and may shorten ED length of stay.

Heparin-Induced Thrombocytopenia in the Critically Ill Patient

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

Heparin-Induced Thrombocytopenia and Thrombosis: Preventing your Thrombolysis Practice from Taking a HITT

Heparin-induced thrombocytopenia and thrombosis (HITT) is an under-recognized cause of deep venous thrombosis treatment failure and of complications during catheter-directed thrombolysis. After a review of HITT pathophysiology, diagnosis, and management, three different cases are presented in this article. Each case highlights subtleties and challenges of HITT diagnosis and management. An example of a practical approach to the diagnosis of HITT is presented.