scholarly journals A practical approach to evaluating postoperative thrombocytopenia

2020 ◽  
Vol 4 (4) ◽  
pp. 776-783 ◽  
Author(s):  
Leslie Skeith ◽  
Lisa Baumann Kreuziger ◽  
Mark A. Crowther ◽  
Theodore E. Warkentin
Keyword(s):  
Platelet Count ◽  
Late Onset ◽  
Practical Approach ◽  
Drug Induced ◽  
Heparin Induced Thrombocytopenia ◽  
Replacement Surgery ◽  
Device Implantation ◽  
Increased Risk ◽  
Posttransfusion Purpura ◽  
Heparin Exposure

Abstract Identifying the cause(s) of postoperative thrombocytopenia is challenging. The postoperative period includes numerous interventions, including fluid administration and transfusion of blood products, medication use (including heparin), and increased risk of organ dysfunction and infection. Understanding normal thrombopoietin physiology and the associated expected postoperative platelet count changes is the crucial first step in evaluation. Timing of thrombocytopenia is the most important feature when differentiating causes of postoperative thrombocytopenia. Thrombocytopenia within 4 days of surgery is commonly caused by hemodilution and increased perioperative platelet consumption prior to thrombopoietin-induced platelet count recovery and transient platelet count overshoot. A much broader list of possible conditions that can cause late-onset thrombocytopenia (postoperative day 5 [POD5] or later) is generally divided into consumptive and destructive causes. The former includes common (eg, infection-associated disseminated intravascular coagulation) and rare (eg, postoperative thrombotic thrombocytopenic purpura) conditions, whereas the latter includes such entities as drug-induced immune thrombocytopenia or posttransfusion purpura. Heparin-induced thrombocytopenia is a unique entity associated with thrombosis that is typically related to intraoperative/perioperative heparin exposure, although it can develop following knee replacement surgery even in the absence of heparin exposure. Very late onset (POD10 or later) of thrombocytopenia can indicate bacterial or fungal infection. Lastly, thrombocytopenia after mechanical device implantation requires unique considerations. Understanding the timing and severity of postoperative thrombocytopenia provides a practical approach to a common and challenging consultation.

Heparin-induced thrombocytopenia: when a low platelet count is a mandate for anticoagulation

Hematology ◽  
2009 ◽  
Vol 2009 (1) ◽  
pp. 225-232 ◽  
Author(s):  
Thomas L. Ortel
Keyword(s):  
Platelet Count ◽  
Heparin Therapy ◽  
Severe Thrombocytopenia ◽  
Drug Induced ◽  
Platelet Factor ◽  
Heparin Induced Thrombocytopenia ◽  
Immune Mediated ◽  
Number Of Patients ◽  
Increased Risk ◽  
Antibody Levels

Abstract Heparin-induced thrombocytopenia (HIT) is an immune-mediated disorder caused by the development of antibodies to platelet factor 4 (PF4) and heparin. The thrombocytopenia is typically moderate, with a median platelet count nadir of ~50 to 60 × 109 platelets/L. Severe thrombocytopenia has been described in patients with HIT, and in these patients antibody levels are high and severe clinical outcomes have been reported (eg, disseminated intravascular coagulation with microvascular thrombosis). The timing of the thrombocytopenia in relation to the initiation of heparin therapy is critically important, with the platelet count beginning to drop within 5 to 10 days of starting heparin. A more rapid drop in the platelet count can occur in patients who have been recently exposed to heparin (within the preceding 3 months), due to preformed anti-heparin/PF4 antibodies. A delayed form of HIT has also been described that develops within days or weeks after the heparin has been discontinued. In contrast to other drug-induced thrombocytopenias, HIT is characterized by an increased risk for thromboembolic complications, primarily venous thromboembolism. Heparin and all heparin-containing products should be discontinued and an alternative, non-heparin anticoagulant initiated. Alternative agents that have been used effectively in patients with HIT include lepirudin, argatroban, bivalirudin, and danaparoid, although the last agent is not available in North America. Fondaparinux has been used in a small number of patients with HIT and generally appears to be safe. Warfarin therapy should not be initiated until the platelet count has recovered and the patient is systemically anticoagulated, and vitamin K should be administered to patients receiving warfarin at the time of diagnosis of HIT.

scholarly journals Heparin-Induced Thrombocytopenia in Healthy Individuals with Continuous Heparin Infusion

TH Open ◽  
2018 ◽  
Vol 02 (01) ◽  
pp. e49-e53
Author(s):  
Jonathan Williams ◽  
Paula Autori ◽  
Stephen Kidd ◽  
Gregory Piazza ◽  
Molly Connors ◽  
...  
Keyword(s):  
Platelet Count ◽  
Unfractionated Heparin ◽  
Healthy Volunteers ◽  
Sleep Medicine ◽  
Healthy Individuals ◽  
Heparin Infusion ◽  
Heparin Induced Thrombocytopenia ◽  
Research Protocols ◽  
Increased Risk ◽  
Heparin Exposure

AbstractThe risk for developing heparin-induced thrombocytopenia in healthy individuals is thought to be low, but monitoring recommendations remain controversial. Therefore, a retrospective cohort study was conducted to identify the incidence of thrombocytopenic events in a healthy research population exposed and re-exposed to continuous intravenous (IV) unfractionated heparin. The Division of Sleep Medicine and the Centre for Clinical Investigations at Brigham and Women's Hospital, Boston, Massachusetts, United States, instituted a standardized platelet monitoring procedure for all research protocols that involved heparin to detect platelet count decreases. Protocol-related frequent blood sampling required use of continuous IV unfractionated heparin infusion (5,000 unit/L in 0.45% saline at 40 mL/h) to maintain line patency over extended periods of IV access. From the years 2009 to 2012, a total of 273 healthy volunteers enrolled in Sleep Medicine research protocols met study criteria as having been exposed and/or re-exposed to continuously infused intravenous heparin for at least 4 hours. The mean continuous heparin exposure time was 88 ± 82 SD hours with a total of 397 heparin exposure and re-exposure events. Platelet count measurements were obtained on 629 occasions, representing a range from 2 to 9 draws per participant. No platelet count decrease of more than 50% was detected. There were no detected adverse bleeding or thrombotic events. In this retrospective study of healthy volunteers involved in a rigorously applied inpatient platelet monitoring protocol, heparin exposure and re-exposure did not lower platelet concentration and, therefore, does not appear to be associated with increased risk of HIT in this population.

Postendarterectomy heparin-induced thrombocytopenia

1988 ◽  
Vol 69 (4) ◽  
pp. 632-634 ◽  
Author(s):  
Larry A. Rogers
Keyword(s):  
Platelet Count ◽  
Vascular Surgery ◽  
Carotid Endarterectomy ◽  
Potential Problem ◽  
Anticoagulation Therapy ◽  
Massive Bleeding ◽  
Drug Induced ◽  
Heparin Induced Thrombocytopenia ◽  
Content Type ◽  
Fine Print

✓ Two episodes of massive bleeding from a sutured arteriotomy were observed within 30 hours after carotid endarterectomy. The patient had received anticoagulation therapy with heparin for 72 hours prior to surgery. A platelet count of 93,000/cu mm was demonstrated following the second hemorrhage. The potential problem of drug-induced thrombocytopenia following vascular surgery is discussed.

The Incidence of Thrombosis in Patients with Isolated Heparin Induced Thrombocytopenia.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 1049-1049 ◽  
Author(s):  
Rachel P. Rosovsky ◽  
Omar I. Abdel-Wahad ◽  
Elizabeth M. Van Cott ◽  
David J. Kuter
Keyword(s):  
Platelet Count ◽  
Mortality Rate ◽  
Massachusetts General Hospital ◽  
Thrombotic Event ◽  
Radiographic Examination ◽  
Platelet Factor ◽  
Heparin Induced Thrombocytopenia ◽  
Total Incidence ◽  
Objective Evidence ◽  
Heparin Exposure

Abstract Introduction: Heparin-induced thrombocytopenia type-II (HIT) is a serious prothrombotic disorder caused by heparin exposure. The incidence of thrombosis in patients with isolated HIT, defined as HIT without clinically evident thrombosis at the time of diagnosis, is not well established. Aim: The purpose of this prospective study was to determine the total incidence of thrombotic events after diagnosis of isolated HIT from radiographic evidence of asymptomatic deep venous thrombosis (DVT) plus radiographic confirmation of symptomatic thrombosis. Patients and Methods: We evaluated all patients with a positive enzyme-linked immunoassay (ELISA) for heparin-platelet factor 4 (PF4) antibody (Ab) daily at Massachusetts General Hospital from 10/10/05 to 5/13/06. Inpatients with (1) a positive PF4 Ab test, (2) thrombocytopenia, as defined by a ≥50% drop from baseline platelet count and/or a fall in platelet count to <150×109/L, in association with heparin exposure, (3) no signs or symptoms of thrombosis at time of the positive Ab test, and (4) no other definitive etiology of thrombocytopenia were considered to have isolated HIT and included for study. Patients with a prior diagnosis of HIT, DVT, pulmonary embolism, or peripheral arterial thrombosis were excluded. Within 72 hours of diagnosis and of initiation of a non-heparin anticoagulant, all included patients underwent radiographic examination for asymptomatic DVT in the lower extremities (LE). Objective evidence of thrombotic events other than LE DVT after the diagnosis was also recorded. Daily platelet count, type and timing of all anticoagulants, use of blood products, and PF4 Ab titer were collected to determine if there was an association between these factors and development of thrombosis. Mortality rate during hospitalization was also recorded. Results: Of the 158 patients with a positive heparin-PF4 Ab, 64 patients met criteria for study, 14 of which were lost to follow-up. Among the 50 remaining eligible patients, the total incidence of thrombosis was 20% (12% were found to have an asymptomatic thrombotic event and 8% developed a symptomatic thrombotic event). Development of thrombosis was independently associated with platelet transfusion (p=0.005) and with the degree of platelet count nadir as expressed by platelet count (p=0.038) or by percent decrease from baseline (p=0.031). There was no association between the PF4 Ab titer or the type and timing of non-heparin anticoagulant and development of thrombosis. The overall mortality rate in patients diagnosed with isolated HIT during hospitalization was 22%. Conclusion: The total incidence of thrombotic events in isolated HIT was 20%, with greater than half of the events being asymptomatic thromboses found only by radiographic examination. This high incidence of asymptomatic LE DVT suggests that routine investigation for LE DVT should be performed in this patient population and that patients with isolated HIT should be treated with a non-heparin anticoagulant. Our findings also confirm the current recommendation to avoid platelet transfusions in patients with isolated HIT as we found an increased rate of thrombosis associated with this practice.

Spontaneous Heparin-Induced Thrombocytopenia Syndrome: Two New Cases and a Proposal For Defining This Disorder

Blood ◽  
2013 ◽  
Vol 122 (21) ◽  
pp. 2328-2328 ◽  
Author(s):  
Theodore E. Warkentin ◽  
Paul Andrew Basciano ◽  
Richard A. Bernstein
Keyword(s):  
Platelet Count ◽  
Platelet Activation ◽  
Research Funding ◽  
Left Vertebral Artery ◽  
Platelet Factor ◽  
Shoulder Hemiarthroplasty ◽  
Heparin Induced Thrombocytopenia ◽  
Activation Assay ◽  
Count Recovery ◽  
Heparin Exposure

Abstract Introduction Heparin-induced thrombocytopenia (HIT) is a transient, autoimmune-like, prothrombotic disorder caused by heparin-dependent, platelet-activating IgG reactive against platelet factor 4/heparin (PF4/H). There is an emerging literature (Am J Med 2008;121:632-6. J Thromb Haemost 2008;6:1598-1600; Thromb Haemost 2013;109:669-75) pointing to rare instances of “spontaneous” HIT in patients without preceding heparin. We report 2 new cases and propose a definition for this controversial disorder. CASE #1. A 62-y.o. man presented with left middle cerebral artery stroke and thrombocytopenia (platelet count, 65×109/L). There was no previous history of thrombocytopenia, surgery, hospitalization, or heparin exposure. Clot extraction performed with heparin was complicated by further platelet count decline to 27 (nadir) and progressive thrombosis of the carotid artery. Aspirin was started, and the platelets recovered to >150 by day 13. CASE #2. A 54-y.o. female developed right leg swelling, left-upper extremity weakness/paresthesias, and thrombocytopenia (61×109/L) 15 days post-shoulder hemiarthroplasty; no intra-/postoperative heparin had been given. Brain MRI demonstrated acute infarct in the left posterior inferior cerebellar artery territory; angiography showed non-visualization of the left vertebral artery. Ultrasound revealed right lower-limb deep-vein thrombosis. Heparin treatment resulted in further platelet count fall to 37 (nadir). Treatment with argatroban, followed by fondaparinux, was associated with platelet count recovery to >150 by day 39. Methods Testing for HIT antibodies was performed by commercial EIA-IgG/A/M (Immucor GTI Diagnostics), in-house EIA-IgG (McMaster), and serotonin-release assay (SRA). Results Both patients’ sera (obtained before any heparin administration) tested strongly positive for HIT antibodies (Table), including strong platelet activation at 0.1 and 0.3 IU/mL heparin, as well as at 0 U/mL heparin, with no platelet activation at 100 IU/mL heparin: these serological features are characteristic of “delayed-onset HIT” (Ann Intern Med 2001;135:502-6). Antibody reactivity declined markedly by 2 to 4 weeks (including loss of platelet-activating properties at 0 IU/mL heparin), in keeping with the usual transience of HIT antibodies (N Engl J Med 2001;344:1286-92), and paralleling both patients’ platelet count recovery. Discussion These cases further support spontaneous HIT as an unusual explanation for acute arterial stroke and thrombocytopenia. One patient had preceding orthopedic surgery, an event previously reported with spontaneous HIT (Thromb Haemost 2013;109:669-75). The strong serum-dependent platelet activation at 0 IU/mL heparin helps to explain how thrombocytopenia and thrombosis can occur in a patient not receiving heparin. RECOMMENDATION. Based on the serological findings of these and previous cases, we propose that a definitive diagnosis of spontaneous HIT syndrome should be based upon all of the following criteria: thrombocytopenia, thrombosis, lack of proximate heparin exposure, strong-positive PF4-dependent immunoassay(s), and a strong-positive platelet activation assay featuring both heparin-dependent (e.g., high heparin neutralization) and heparin-independent platelet activation (at 0 IU/mL heparin). Disclosures: Warkentin: Pfizer Canada: Honoraria; Paringenix: Consultancy; Immucor GTI Diagnostics: Research Funding; WL Gore: Consultancy; GSK: Research Funding.

Management of the multiple phases of heparin-induced thrombocytopenia

2016 ◽  
Vol 116 (11) ◽  
pp. 835-842 ◽  
Author(s):  
Adam Cuker
Keyword(s):  
Platelet Count ◽  
Key Management ◽  
Vitamin K Antagonists ◽  
Oral Anticoagulants ◽  
Direct Oral Anticoagulants ◽  
Vena Cava ◽  
Hepatic Function ◽  
Heparin Induced Thrombocytopenia ◽  
Increased Risk ◽  
Count Recovery

SummaryThe clinical course of heparin-induced thrombocytopenia (HIT) may be separated into five sequential phases: 1. suspected HIT, 2. acute HIT, 3. subacute HIT A, 4. subacute HIT B, and 5. remote HIT. Each phase confronts the clinician with a unique set of management questions. In this review, the phases of HIT are defined and key management questions associated with each phase are discussed. Among patients with Suspected HIT, I use the 4Ts score to determine which patients have a sufficiently high probability of HIT to justify discontinuation of heparin and initiation of a non-heparin parenteral anticoagulant. An algorithm for selecting an appropriate non-heparin anticoagulant based on the patient’s clinical stability, renal and hepatic function, drug availability, and physician comfort is provided. In patients with Acute HIT, I generally avoid prophylactic platelet transfusion and inferior vena cava filter insertion because of a potential increased risk of thrombosis. I perform 4-limb screening compression ultrasonography. In patients with symptomatic thromboembolism or asymptomatic proximal deep-vein thrombosis, I treat with anticoagulation for three months. In patients without thrombosis, I discontinue anticoagulation upon platelet count recovery. I do not transition patients to an oral anticoagulant until platelet count recovery (i. e. Subacute HIT A). I increasingly choose direct oral anticoagulants over vitamin K antagonists in this setting because of their greater convenience and safety. In Subacute HIT B and Remote HIT, I use heparin for cardiovascular surgery, whereas I use bivalirudin in patients with Acute HIT and Subacute HIT A in whom surgery cannot be delayed.

Dosing Patterns and Outcomes in African American, Asian, and Hispanic Patients with Heparin-Induced Thrombocytopenia Treated with Argatroban.

Blood ◽  
2008 ◽  
Vol 112 (11) ◽  
pp. 3403-3403
Author(s):  
Marcie J Hursting ◽  
Ik-Kyung Jang
Keyword(s):  
African American ◽  
Platelet Count ◽  
African Americans ◽  
Clinical Outcomes ◽  
Major Bleeding ◽  
Heparin Induced Thrombocytopenia ◽  
Increased Risk ◽  
Hispanic Patients ◽  
Ischemic Complications ◽  
Dosing Patterns

Abstract Nonwhites, as compared with whites, have increased risk for thromboembolic complications in heparin-induced thrombocytopenia (HIT) (Lewis et al, Chest 2006). To better characterize the risk in nonwhite patients, we retrospectively evaluated dosing patterns and clinical outcomes in African American, Asian, and Hispanic patients administered argatroban therapy for clinically diagnosed HIT. Patients were from previously reported, multicenter, prospective studies of argatroban therapy (2 mcg/kg/min, adjusted to achieve aPTTs 1.5–3 times baseline) in HIT (defined as an otherwise unexplained platelet count <100 x109/L, or 50% reduction in platelet count, following heparin therapy). For African American (n=52), Asian (n=13), and Hispanic (n=14) patient groups, baseline characteristics, therapeutic argatroban dose and duration, aPTTs during therapy, and clinical outcomes (death, including death due to thrombosis; amputation, including amputation secondary to ischemic complications of HIT; new thrombosis; and major bleeding within a 37-day period) were summarized and compared. Among groups, no differences were detected in demographic or baseline features, excepting weight (median values: 62, 77 and 85 kg, respectively, for Asians, African Americans, and Hispanics). Median baseline platelet counts were 45–71 x109/L, and approximately 50% of patients in each group had HIT-related thrombosis before argatroban was initiated. Each group received a similar duration of argatroban therapy (4.0–5.5 days), yet Asians needed a lesser dose (1.0 mcg/kg/ min, versus 1.9 mcg/kg/min in other groups) to achieve comparable aPTTs (61–69 s). New thrombosis occurred most often in African Americans (21%, versus 7–8% in other groups) and when baseline HIT-related thrombosis was present (9/13 events, 69%). Amputation occurred most often in Hispanics (21%, versus 0–12% in other groups) and when diabetes was present (6/9 events, 67%). Mortality was 21–31%, and mortality due to thrombosis was 0–7%. Asians had the lowest frequency of any thrombotic-related outcome (composite of death due to thrombosis, amputation secondary to ischemic complications of HIT, or new thrombosis: 8%, versus 27–29% in other groups). Two patients, each African American, experienced major bleeding (gastrointestinal), for an overall major bleeding rate of 2.5% and by-group rates of 0–4%. Although limited by small group sizes, our study is among the first to characterize outcomes in minority patients administered nonheparin therapy for HIT. Our findings suggest that, despite achieving comparable levels of anticoagulation with argatroban, African Americans and Hispanics are higher risk patients than Asians for poor outcomes in HIT and also that in minority patients with adverse outcomes, baseline HIT-related thrombosis or diabetes is often present.

Heparin-Induced Thrombocytopenia in Cancer

2011 ◽  
Vol 9 (7) ◽  
pp. 781-787 ◽  
Author(s):  
Benjamin J. Miriovsky ◽  
Thomas L. Ortel
Keyword(s):  
Cancer Patients ◽  
Common Finding ◽  
Clinical Settings ◽  
Drug Induced ◽  
Heparin Induced Thrombocytopenia ◽  
Increased Risk ◽  
Risk For Thrombosis ◽  
Important Drug

Heparin-induced thrombocytopenia is a common and clinically important drug-induced complication that can cause life- and limbthreatening thrombosis. Epidemiologically, the disease has been studied in many different clinical settings, but little is known about it in cancer patients, a population at increased risk for thrombosis and thus exposure to heparin products. Additionally, thrombocytopenia is a common finding in cancer patients. The convergence of these variables highlights the importance of an increased understanding of the disease in cancer patients.

scholarly journals Drug-associated thrombocytopenia

Hematology ◽  
2018 ◽  
Vol 2018 (1) ◽  
pp. 576-583 ◽  
Author(s):  
Tamam Bakchoul ◽  
Irene Marini
Keyword(s):  
Platelet Count ◽  
Clinical Symptoms ◽  
Scoring Systems ◽  
Severe Thrombocytopenia ◽  
Thromboembolic Complications ◽  
Drug Induced ◽  
Increased Risk ◽  
High Doses ◽  
Risk Of Hemorrhage

Abstract 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.

Dietary Hypercholesterolemia Enhances Heparin-Induced Thrombocytopenia/Thrombosis: A Prothrombotic Risk Factor in a Transgenic Mouse Model.

Blood ◽  
2005 ◽  
Vol 106 (11) ◽  
pp. 56-56 ◽  
Author(s):  
Michael P. Reilly ◽  
Scott K. Dessain ◽  
Scott M. Taylor ◽  
M. Anna Kowalska ◽  
Mortimer Poncz ◽  
...  
Keyword(s):  
Mouse Model ◽  
Atherogenic Diet ◽  
Standard Diet ◽  
Generation Model ◽  
Drug Induced ◽  
Platelet Factor ◽  
Thrombotic Risk ◽  
Heparin Induced Thrombocytopenia ◽  
Increased Risk

Abstract Heparin-induced thrombocytopenia/thrombosis (HIT/T), the most frequent drug-induced immune thrombocytopenia, is a common cause of life- and limb-threatening thrombosis. Although heparin/platelet factor 4 (PF4) antibodies are detected in many patients treated with heparin, there is little understanding of why only a subset of patients develops thrombosis. We recently produced and characterized the first mouse model that recapitulates the salient features of the disease. A second generation model, designated IIA/hPF4-mPF4KO, expresses human FcγRIIA and PF4 but lacks endogenous mouse PF4. These models allow systematic investigations of factors that contribute to pathogenic consequences of HIT/T antibodies. In the current study, we hypothesize that hypercholesterolemia, a known stimulus for atherosclerosis, endothelial dysfunction, and platelet hyperreactivity, would augment thrombosis in our mouse model of HIT/T. Age and sex-matched IIA/hPF4-mPF4KO mice were fed an atherogenic diet (Paigen diet) (AD; 15% cocoa butter, 1% cholesterol, 0.5% cholate) (n=10) or maintained on standard diet (SD; 4.5% fat, no cholate) (n=10). Mice fed the AD for only 4 weeks had significantly increased cholesterol levels (173 ± 29 mg/dl vs. 50 ± 18 mg/dl for SD-fed; p &lt; 0.0001). Mice were then injected with 30 U heparin and KKO, a mouse monoclonal heparin/PF4 antibody. The mean nadir platelet count in AD-fed mice was 34.6% ± 9.1 lower than that in the SD-fed mice (p&lt; 0.0001). Thrombin-anti-thrombin III (TAT) levels, which reflect thrombin generation in vivo, in the AD-fed mice increased from 32 ± 5 μg/at baseline to 79 ± 16 μg/l (p &lt; 0.0001) coincident with the platelet nadir. In contrast, SD-fed mice, with a less profound fall in platelets, showed no increase in TAT. Histological examination showed multiple platelet-fibrin thrombi in lungs and livers of AD-fed mice, whereas the SD-fed mice showed no histological evidence of thrombosis. Thus, in our mouse model, short-term diet-induced hyperlipidemia significantly increases the severity of heparin/PF4 antibody-mediated thrombocytopenia and thrombosis. Our studies provide evidence that a specific host factor can enhance the pathologic effects of heparin/PF4 antibodies in vivo and contribute to thrombotic risk in patients with HIT/T. An increased understanding of the contribution of prothrombotic factors not only will facilitate identification of patients with heparin/PF4 antibodies who are at increased risk of thrombosis, but also provide novel approaches to treatment of HIT/T.

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