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

Management of heparin-induced thrombocytopenia

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is a rare but severe prothrombotic adverse effect of heparin treatment. The underlying cause is the formation of highly immunogenic complexes between negatively charged heparin and positively charged platelet factor 4 (PF4). Resulting antibodies against these PF4/heparin complexes can activate platelets via the platelet FcγIIa receptor, leading to thrombin generation and thus to the paradox of a prothrombotic state despite thrombocytopenia and application of heparin. Prompt diagnosis of HIT is important in order to change treatment to prevent severe thromboembolic complications. However, this is often difficult as thrombocytopenia is frequent in hospitalized patients and the commercially available laboratory tests for HIT antibodies have a high negative predictive value but only a poor positive predictive value. This leads to overdiagnosis and overtreatment of HIT, which also bear the risk for adverse outcomes.

AREAS COVERED

This review aims at resuming recent data on HIT, thereby focusing on the role of new anticoagulants and providing a framework for diagnosis and treatment. Furthermore, it provides some insights into the pathogenesis of this peculiar adverse drug reaction and ventures a guess at its future relevance in clinical practice.

EXPERT OPINION

New drugs which are strongly negatively charged should be assessed for their capacity to form complexes with PF4. If they do so, they bear the risk of inducing a HIT-like immune response. The immunology of HIT is still largely unresolved. Understanding HIT might provide insights into other immune and autoimmune response mechanisms.

Does my patient have a life- or limb-threatening thrombocytopenia?

The diagnosis and management of severe thrombocytopenias can be difficult, but is necessary to avoid significant morbidity and mortality. The causes of severe thrombocytopenias, often with a platelet count of less than 10 × 10(9)/L, include heparin-induced thrombocytopenia, the thrombotic microangiopathies, the catastrophic antiphospholipid syndrome, preeclampsia/HELLP, and posttransfusion purpura. This review provides a brief overview of the key clinical features of each of these major clinical entities, and strategies for their diagnostic workup and therapeutic management.

Usefulness of anti-PF4/heparin antibody test for intensive care unit patients with thrombocytopenia

BACKGROUND

It is critical to differentiate heparin-induced thrombocytopenia (HIT) from disseminated intravascular coagulation (DIC) in heparinized intensive care unit (ICU) patients with thrombocytopenia because the therapeutic approach differs based on the cause. We investigated the usefulness of PF4/heparin antibody tests in these patients.

METHODS

A total of 127 heparinized ICU patients whose platelet counts were <150×10(9)/L or reduced by >50% after 5-10 days of heparin therapy were enrolled. PF4/heparin antibodies were measured using 2 immunoassays. We assessed the probability of HIT by using Warkentin's 4T's scoring system for antibody positive patients and compared routinely performed coagulation test results between patients with and without antibodies to evaluate the ability of these tests to discriminate between HIT and DIC.

RESULTS

Positive results were obtained for 14 (11.0%) and 11 (8.7%) patients in the 2 assays. The analysis performed using the 4T's scoring system revealed that 11 of 20 (15.7%) patients with antibodies in at least 1 assay had intermediate or greater probability of HIT. Patients without antibodies had significantly higher levels of D-dimer than those with antibodies. However, there were no intergroup differences in platelet counts, PT, aPTT, fibrinogen, DIC score, and rate of overt DIC.

CONCLUSION

Seropositivity for PF4/heparin antibody was 8.7-11.0% in the patients with thrombocytopenia, and more than a half of them had an increased probability of HIT. Among the routine coagulation tests, only D-dimer was informative for differentiating HIT from DIC. PF4/heparin antibody test is useful to ensure appropriate treatment for thrombocytopenic heparinized ICU patients.

Heparin-induced thrombocytopenia in essential thrombocytosis

We report a 67-year-old woman with essential thrombocytosis who developed cerebral infarction and heparin-induced thrombocytopenia during treatment for the cerebral infarction. She developed additional cerebral infarcts, acute femoral artery occlusion, and thrombophlebitis of her lower extremities. She was successfully treated with argatroban. This is the first report of a patient with essential thrombocytosis who developed heparin-induced thrombocytopenia and serious conditions, which included multiple thromboembolisms and coagulation disorders mimicking disseminated intravascular coagulation.

Early post-operative thrombosis of the prosthetic mitral valve in patient with heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is one of the most common immune-mediated adverse drug reactions, with frequencies as high as 2-3% for certain groups of post-cardiac surgery patients. We report on an 50-year-old woman with early post-operative thrombosis of the prosthetic mitral valve due to heparin-induced thrombocytopenia. Non-invasive imaging (two-dimensional transesophageal echocardiography; 2D-TEE) allowed the exact localisation of thrombotic masses and revealed the increase of the mean diastolic mitral gradient. The HIT diagnosis was proved by the clinical scoring system, and with the identification of heparin platelet factor 4-induced antibodies. After the withdrawal of LMWH therapy and the start of intravenous lepirudin treatment, the patient's medical condition improved continuously. Follow-up echocardiography showed a step-wise decrease in the severity of the mean diastolic mitral valve gradient and a complete resolution of thrombus formations. Perhaps we may remind ourselves that, whilst HIT is one of the most common immune-mediated adverse drug reactions for certain groups of post-cardiac surgery patients, it can be managed successfully. We would also stress the importance of serial 2D-TEE examinations in the early post-operative period.

PF4/heparin antibody testing and treatment of heparin-induced thrombocytopenia in the intensive care unit

BACKGROUND

The diagnosis of heparin-induced thrombocytopenia (HIT) may be challenging in critically ill patients, as heparin exposures are ubiquitous, and thrombocytopenia is common. Unwarranted ordering and incorrect interpretation of heparin antibody tests can expose a patient to adverse drug events and imposes a significant economic burden on our health care system.

METHODS

A prospective, observational study was performed over 4 months on all adult patients located in 5 intensive care units, with a heparin antibody test ordered.

RESULTS

A platelet factor 4/heparin enzyme-linked immunosorbent assay (ELISA) test was ordered in 131 patients. In total, 110 patients had a low 4Ts score (0-3), and of these 103 had a negative ELISA result. In patients with a low 4Ts score, 0 (0%) of 110 had an optical density value >1.0. One hundred twenty-nine patients (98%) had another possible cause of thrombocytopenia identified.

CONCLUSION

In critically ill patients, low 4Ts scores indicate a low probability of HIT, and heparin antibody testing in these patients is not useful.

How I treat heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia is a prothrombotic adverse drug effect induced by platelet-activating antibodies against multimolecular complexes of platelet factor 4 and heparin. Diagnosis rests on a clinical assessment of disease probability and laboratory testing. Management involves immediate discontinuation of heparin and initiation of an alternative anticoagulant. Because of the frequency of thrombocytopenia among heparinized patients, the limited specificity of widely available immunoassays, the limited availability of more specific functional assays, and clinicians' fears of missing a case of true disease, overtesting, overdiagnosis, and overtreatment have become common. As a result, a substantial number of thrombocytopenic patients are unnecessarily exposed to costly alternative anticoagulants and their attendant risk of bleeding. In this review, we describe not only our approach to the evaluation and management of patients with heparin-induced thrombocytopenia, but also the measures we use to minimize misdiagnosis and unnecessary treatment of patients without the disease. In addition, we propose areas of investigation for improvement of the diagnosis and management of this potentially fatal disorder.

Frequency of heparin/platelet factor 4-dependent platelet antibodies in patients undergoing angioplasty and stenting for cardiovascular disease and their role for on-clopidogrel platelet reactivity

BACKGROUND

The frequency of heparin-induced platelet antibodies (H/PF4 antibodies) following heparin exposure during percutaneous intervention with stent implantation is unknown. These antibodies may activate platelets and therefore contribute to high on-clopidogrel residual platelet reactivity (HRPR).

METHODS

We screened 288 patients after angioplasty and stenting for H/PF4 antibodies by an IgG/A/M ELISA. The 44 (15.3%) positive samples were further evaluated for IgG only antibodies, by the particle gel immunoassay (PaGIA), the heparin induced platelet activation assay (HIPA) and MEA. Further, we determined on-treatment platelet reactivity by multiple electrode aggregometry (MEA) in these patients. In vivo platelet activation was assessed by P-selectin expression.

RESULTS

The prevalence of H/PF4 antibodies in the total patients' cohort was 15.3% (95% CI 11.3-20%) by the IgG/A/M ELISA, 9.4% (95% CI 6.3-13.4%) by the IgG ELISA, 11.5% (95% CI 8-15.7%) by PaGIA, 14.2% (95% CI 10.4-18.8%) by MEA, and 2.4% (95% CI 1-4.9%) by HIPA. On-treatment platelet reactivity was similar between patients without and with H/PF4 antibodies [39 AU (6-110 AU) vs. 41 AU (7-91 AU); P = 0.85]. HRPR was seen in 105 patients (37.5%), and occurred to a similar extent in patients without and with H/PF4 antibodies in all test systems (all P > 0.2). Further, there was no difference of the ELISA optical densities using the IgG/A/M or the IgG only ELISA between patients without or with HRPR (all P > 0.3). There was no significant difference of P-selectin expression between patients without or with H/PF4 antibodies (P = 0.97). Noteworthy, none of the patients who developed H/PF4 antibodies had heparin-induced thrombocytopenia or a thromboembolic event.

CONCLUSION

H/PF4 antibodies are not rare in patients undergoing angioplasty and stenting. However, these antibodies are not associated with the occurrence of HRPR.

Validation of whole blood impedance aggregometry as a new diagnostic tool for HIT: results of a large Australian study

Heparin-induced thrombocytopenia (HIT) remains a challenge, with diagnosis confirmed only by functional assays. The gold standard 14C-serotonin release assay (SRA) is highly sensitive but technically challenging and unsuitable for routine use. We conducted a large study to validate whole blood impedance aggregometry (WBIA) as a suitable diagnostic tool for HIT. WBIA and SRA were used to test 181 samples positive for H-PF4 antibodies by PaGIA or ELISA. Using the same high responder donor, 77 samples were positive by WBIA (aggregation with low-dose but not high-dose heparin). Using the strict definition for SRA positivity, 72 samples were true HIT. In nine samples, serotonin release with high-dose heparin dropped by > 50% but was still >20%; these were retested after a one-half dilution and 8/9 became positive. Ten other samples were discrepant between the two assays: one strongly positive (89% release) and six weakly positive samples by SRA (average release 56%) were WBIA negative. When these samples were retested using a random donor, only two remained SRA positive. Three samples were strongly WBIA positive but SRA negative; two were retested by SRA with 0.5IU/ml heparin and one became positive. Under controlled conditions, using the same selected high-responder donor, WBIA and SRA performed similarly with slightly increased sensitivity of the WBIA when using the strict definition of SRA positivity. WBIA is easy to perform with rapid turn-around time and warrants a multi-laboratory trial to complete its validation as a confirmatory assay for platelet-activating HIT antibodies.

Thrombosis in suspected heparin-induced thrombocytopenia occurs more often with high antibody levels

OBJECTIVE

The study objective was to determine whether higher antiplatelet factor 4 (PF4)/heparin antibody levels using an enzyme-linked immunosorbent assay are associated with more frequent thrombotic events in patients with clinically suspected heparin-induced thrombocytopenia. Heparin-induced thrombocytopenia is an immune-mediated adverse drug reaction. An enzyme-linked immunosorbent assay detects anti-PF4/heparin antibodies to support a suspected clinical diagnosis of heparin-induced thrombocytopenia. The utility of quantitative enzyme-linked immunosorbent assay results is uncertain.

METHODS

Our single-centered study evaluated quantitative anti-PF4/heparin antibody levels using an enzyme-linked immunosorbent assay in consecutive hospitalized patients with a clinical suspicion of heparin-induced thrombocytopenia and positive anti-PF4/heparin antibody levels between July 2003 and December 2006.

RESULTS

Overall, anti-PF4/heparin antibody values were available for 318 patients with clinically suspected heparin-induced thrombocytopenia. The median level was 0.85 optical density units (range 0.31-4.0). The overall rate of arterial or venous thrombosis was 23.3%. A 1-unit increase in anti-PF4/heparin antibody level was associated with an approximate doubling in the odds of thrombosis by 30 days (odds ratio, 1.9; 95% confidence interval, 1.5-2.6; P=.0001). The proportion of patients with pulmonary embolism increased with higher anti-PF4/heparin antibody levels.

CONCLUSION

Higher levels of anti-PF4/heparin antibody are associated with increased thrombosis risk among patients with clinically suspected heparin-induced thrombocytopenia and might have clinical utility for prediction of true heparin-induced thrombocytopenia and the development of thrombosis.

Dabigatran Use in a Postoperative Coronary Artery Bypass Surgery Patient with Nonvalvular Atrial Fibrillation and Heparin-PF4 Antibodies

OBJECTIVE:

To present a case of dabigatran use for nonvalvular atrial fibrillation in a patient from a population for whom it has not been studied. Postoperative coronary artery bypass patients have significant bleeding risk and potential to develop heparin-induced thrombocytopenia (HIT).

CASE SUMMARY:

A 70-year-old male with a history of paroxysmal atrial fibrillation in sinus rhythm prior to surgery developed atrial fibrillation on postoperative day 2 after coronary artery bypass surgery. Because of thrombocytopenia, anticoagulation to decrease stroke risk with atrial fibrillation was initiated with dabigatran 150 mg orally twice daily beginning on postoperative day 4. Later on postoperative day 4, after dabigatran was administered, the patient's HIT screening test was positive for heparin/PF4 antibodies; however, he was not clinically diagnosed with HIT. Heparin was not used postoperatively and transition dosing from dabigatran to warfarin was started on postoperative day 8, the day of discharge. At the time of the outpatient follow-up appointment, the patient had no signs of thrombosis or bleeding complications.

DISCUSSION:

Dabigatran is a direct thrombin inhibitor approved for nonvalvular atrial fibrillation. In this case, the physician ordered dabigatran for an approved use, according to manufacturer labeling. However, patients with this diagnosis would have been excluded from the RE-LY (Randomized Evaluation of Long-term Anticoagulant Therapy) trial, on which Food and Drug Administration approval was based. Our patient had thrombocytopenia with a low pretest probability for HIT but was positive for heparin/PF4 antibodies, based on enzyme immunoassay testing. Dabigatran was continued for atrial fibrillation and not switched to any other direct thrombin inhibitor, such as argatroban, lepirudin, or bivalirudin, which are listed in the American College of Chest Physicians Evidence-Based Clinical Practice Guidelines, 8th edition, for the Treatment and Prevention of Heparin Induced Thrombocytopenia.

CONCLUSIONS:

Further research on the use of dabigatran in patients with recent coronary bypass surgery and heparin/PF4 antibodies is needed before any recommendations can be made.

Adverse effects of heparin

All the adverse effects of heparins are related to their wide variety of biological activities, with bleeding being the most important safety issue, resulting directly from the potency of heparin as an anticoagulant. However, it is hard to define the bleeding risk, since it depends on numerous parameters including the indication, dosage, method, and duration of heparin application, the clinical study design and definition of bleeding as well as patient characteristics and determinants of bleeding such as type of surgery and co-medication. Nonbleeding complications of heparins are caused by binding of heparin molecules to proteins other than antithrombin and to cells, which is generally more pronounced with unfractionated heparin than with low-molecular-weight heparins. Accordingly, heparin-induced thrombocytopenia, the most severe nonbleeding adverse reaction, occurs about 10 times less with low-molecular-weight heparins than with unfractionated heparin. Frequent and therefore important adverse reactions of heparins are skin lesions resulting from delayed-type hypersensitivity reactions. All the other undesirable effects are discussed as well, but they are mostly clinically irrelevant.

Hematology and Oncology in Critical Illness

This chapter will focus on a variety of hematologic issues pertinent to the care of critically ill children. This is an area of intense research with the pathophysiology underlying these clinical conditions becoming progressively better understood. This improved understanding has resulted in new therapeutic strategies that are being assessed in multicenter clinical trials. The chapter will begin by describing the incidence and pathophysiologic significance of anemia in the pediatric intensive care unit (PICU) providing a differential diagnosis of the many conditions that may present with anemia in this setting. The chapter will next consider disseminated intravascular coagulation (DIC) focusing on the pathophysiology of a condition that has been associated with much morbidity and mortality. The underlying conditions predisposing to DIC will be detailed as well as a number of treatment options that have been implemented in clinical trials. In addition to DIC, thrombocytopenia may be caused by a number of other clinical conditions important to the pediatric critical care provider. The clinical and prognostic significance of thrombocytopenia will be addressed and a focused differential diagnosis will be provided. Thrombotic disorders are becoming increasingly recognized in children and are a particular concern for the pediatric intensivist. The epidemiology of thromboembolism in children will be reviewed focusing on the conditions most commonly associated with these thromboses. Finally, a chapter on hematologic issues in the critically ill child would not be complete without a discussion of sickle cell disease. Acute chest syndrome, one of the most frequent complications of sickle cell disease resulting in the need for intensive care services, will be discussed in detail.

Heparin-induced thrombocytopenia in the pediatric population: a review of current literature

Heparin-induced thrombocytopenia is a rare and serious reaction to unfractionated heparin and low-molecular-weight heparins in children. Quick recognition, discontinuation of heparin, and subsequent treatment with an alternative anticoagulant are essential steps to prevent serious complications such as thrombus and limb amputation. The purpose of this review is to describe the clinical features of heparin-induced thrombocytopenia in children and to summarize the data available for its management. This paper summarizes data and relates the use of direct thrombin inhibitors with clinical outcomes. A literature search was conducted with Ovid, using the key terms argatroban, bivalirudin, hirulog, danaparoid, lepirudin, direct thrombin inhibitor, heparin-induced thrombocytopenia, thrombosis, warfarin, and fondaparinux. Articles were excluded if they were classified as editorials, review articles, or conference abstracts or if they involved patients 18 years of age or older or described disease states not related to thrombosis. Nineteen articles containing 33 case reports were identified and evaluated for this review. Of the 33 cases, 14, 10, 4, and 2 cases described the use of lepirudin, danaparoid, argatroban, and bivalirudin, respectively. Two cases did not report the type of anticoagulant used, and 1 case used aspirin. The most commonly reported complication was bleeding.

Results of a consensus meeting on the use of argatroban in patients with heparin-induced thrombocytopenia requiring antithrombotic therapy - a European Perspective

Argatroban has been introduced as an alternative parenteral anticoagulant for HIT-patients in several European countries in 2005. In 2009 a panel of experts discussed their clinical experience with argatroban balancing risks and benefits of argatroban treatment in managing the highly procoagulant status of HIT-patients. This article summarizes the main conclusions of this round table discussion. An ongoing issue is the appropriate dosing of argatroban in special patient groups. Therefore, dosing recommendations for different HIT-patient groups (ICU patients; non-ICU patients, paediatric patients, and for patients undergoing renal replacement therapies) are summarized in this consensus statement. Because of the strong correlation between argatroban dosing requirements and scores used to characterize the severity of illness (APACHE; SAPS, SOFA) suitable dosing nomograms are given. This consensus statement contributes to clinically relevant information on the appropriate use and monitoring of argatroban based on the current literature, and provides additional information from clinical experience. As the two other approved drugs for HIT, danaparoid and lepirudin are either currently not available due to manufacturing problems (danaparoid) or will be withdrawn from the market in 2012 (lepirudin), this report should guide physicians who have limited experience with argatroban how to use this drug safely in patients with HIT.

Heparin-Induced Thrombocytopenia Screening and Management in Pediatric Patients

The diagnosis and management of heparin-induced thrombocytopenia (HIT) in pediatric patients poses significant challenges. The cardinal findings in HIT, thrombocytopenia and thrombosis with heparin exposure, are seen commonly in critically ill children, but are most often secondary to etiologies other than HIT. However, without prompt diagnosis, discontinuation of heparin, and treatment with an alternative anticoagulant such as a direct thrombin inhibitor (DTI), HIT can result in life- and limb-threatening thrombotic complications. Conversely, DTIs are associated with higher bleeding risks than heparin in adults and their anticoagulant effects are not rapidly reversible; furthermore, the experience with their use in pediatrics is limited. Whereas immunoassays are widely available to aid in diagnosis, they carry a significant false positive rate. Age-dependent differences in the coagulation and immune system may potentially affect manifestations of HIT in children, but have not been extensively examined. In this chapter, diagnostic approaches and management strategies based on a synthesis of the available pediatric studies and adult literature on HIT are discussed.

Recent advances in heparin-induced thrombocytopenia

PURPOSE OF REVIEW

Heparin-induced thrombocytopenia (HIT) is a prothrombotic complication of heparin therapy caused by antibodies against platelet factor 4/heparin complexes. Progress in our understanding of HIT has translated to improvements in treatment and patient outcomes. The objective of this review is to examine recent advances and highlight areas of future inquiry in the epidemiology, diagnosis, and management of this potentially fatal disorder.

RECENT FINDINGS

Risk factors for the development of HIT related to heparin administration are well described. Recent identification of host-related risk factors adds to our understanding of disease epidemiology. The limited specificity of clinical diagnosis and widely used immunologic assays for HIT results in frequent overdiagnosis. Novel clinical decision rules and laboratory assays to improve diagnosis are in development. Fondaparinux, bivalirudin, and desirudin have recently been added to the HIT armamentarium.

SUMMARY

Despite these advances, critical issues remain to be addressed. Future research efforts will focus on the identification of novel clinical risk factors and biomarkers that will enable recognition of individuals at greatest risk, optimization of diagnostic strategies and use of currently available therapeutics, and development of new drugs that not only reduce thrombotic complications, but also minimize bleeding risk, are well tolerated in patients with organ dysfunction, and facilitate transition to outpatient therapy.

[The platelet and its challenges]

Thrombocytopenia is frequently observed in intensive care medicine, and it is associated with increased mortality. The causes of thrombocytopenia are manifold and several conditions may occur simultaneously so that an exact correlation with a single etiology may be difficult. The present case report demonstrates the importance of an appropriate pathophysiological and clinical consideration in order to avoid misdiagnoses and inappropriate management.

The Syk-kinase inhibitor R406 impairs platelet activation and monocyte tissue factor expression triggered by heparin-PF4 complex directed antibodies

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is a rare but severe complication of heparin therapy in which immunoglobulin G (IgG) antibodies against the platelet factor 4-heparin complex activate platelets through the FcγRIIA receptor. Clustering of FcγRIIA initiates signaling cascades involving tyrosine kinases including the spleen tyrosine kinase (Syk). Moreover, besides the critical role of platelets, the expression of tissue factor (TF) by human monocytes triggered by HIT antibodies has been shown to contribute to the hypercoagulability and the thrombotic complications in HIT patients.

OBJECTIVES

We investigated the effect of R406, a small molecule inhibitor of Syk developed as a potential treatment of autoimmune diseases, allergic disorders and B-cell related hematological malignancies, on FcγRIIA-mediated platelet activation. To further assess the potential activity of Syk inhibitors in HIT treatment, the effect of R406 was also evaluated on HIT antibodies-induced expression of TF and procoagulant activity of monocytic cells.

RESULTS

We show that R406 is a potent inhibitor of platelet signaling and functions initiated by FcγRIIA cross-linking by specific antibodies or by sera from HIT patients. Syk inhibition efficiently prevents FcγRIIA-induced LAT phosphorylation and activation of phosphoinositide 3-kinase, Akt, phospholipase Cγ2 and p38 MAP-kinase. As a consequence, FcγRIIA-induced platelet aggregation, granule secretion and microparticles production are strongly inhibited by R406. Moreover, the Syk inhibitor efficiently impairs the expression of TF and the procoagulant activity of human monocytes triggered by HIT antibodies.

CONCLUSION

Syk inhibitors may be of therapeutic interest in the treatment of HIT by reducing HIT antibodies-mediated platelet activation and monocyte procoagulant activity.

Rapid exclusion or confirmation of heparin-induced thrombocytopenia: a single-center experience with 1,291 patients

BACKGROUND

The current gold-standard for diagnosing heparin-induced thrombocytopenia is the detection of platelet-activating antibodies by means of functional assays which, since they are time consuming and not widely available, are not suited to guiding acute treatment decisions. The objective of our study was to assess the ability of more rapid immunoassays to predict the presence of functionally relevant anti-platelet factor 4/heparin-antibodies.

DESIGN AND METHODS

We analyzed 1,291 of 1,383 (93.4%) patients consecutively evaluated for suspected heparin-induced thrombocytopenia at our institution. Clinical pre-test probability was defined by the 4T-score. Anti-platelet factor 4/heparin-antibodies were measured with three immunoassays (ID-H/PF4-PaGIA, Asserachrom-HPIA, and GTI-PF4) and their functional relevance was assessed by a two-point heparin-induced platelet aggregation test. Performance of the immunoassays was evaluated by receiver operating characteristic analysis.

RESULTS

Among 1,291 patients, 96 (7.4%) had a positive heparin-induced platelet aggregation-test: 7 of 859 (0.8%) with a low, 50 of 358 (14.0%) with an intermediate, and 39 of 74 (52.7%) with a high 4T-score. Receiver operating characteristics analysis indicated that best immunoassay thresholds for predicting a positive platelet aggregation test were: Titer of 4 or more (ID-H/PF4-PaGIA), optical density more than 0.943 (Asserachrom-HPIA) and more than 1.367 (GTI-PF4). A 100% negative predictive value was observed at the following thresholds: Titer of 1 or under (ID-H/PF4-PaGIA), optical density less than 0.300 (Asserachrom-HPIA) and less than 0.870 (GTI-PF4). A 100% positive predictive value was reached only by ID-H/PF4-PaGIA, at titers of 32 or over. Positive and negative likelihood ratios were calculated for results between the thresholds with 100% negative or positive predictive value.

CONCLUSIONS

We show that: i) negative and weak positive results of immunoassays detecting anti-platelet factor 4/heparin-antibodies exclude heparin-induced thrombocytopenia; ii) anti-platelet factor 4/heparin-antibody titers of 32 or over (ID-H/PF4-PaGIA) have a 100% positive predictive value for functionally relevant antibodies; iii) combining the clinical pre-test probability with the likelihood ratio of intermediate immunoassay results allows assessment of post-test probability for heparin-induced thrombocytopenia in individual patients.

Donor heparinization is not a contraindication to liver transplantation even in recipients with acute heparin-induced thrombocytopenia type II: a case report and review of the literature

Heparin-induced thrombocytopenia (HIT) type II is caused by an immune-mediated side effect of heparin anticoagulation resulting in a clotting disorder. In the setting of urgent liver transplantation, the question arises whether a graft from a heparinized donor can be safely transplantated in a recipient with even acute heparin-induced thrombocytopenia type II. We report on a patient with end-stage liver disease and acute HIT II waiting for liver transplantation. Despite the risk of life-threatening complications, an organ procured from a heparinized donor was accepted. Assuming heparin residuals within the graft, the donor organ was flushed backtable with increased amounts of Wisconsin solution. The subsequent transplantation and the postoperative course were uneventful; neither thromboses nor graft dysfunction occurred. Even in acute episode of HIT II with circulating antibodies, a patient may receive an organ from a heparin-treated donor, if adequate precautions during organ preparation are observed.

[Ischemic stroke and heparin-induced thrombocytopenia]

Immune-mediated heparin-induced thrombocytopenia (HIT) is a rare but serious side effect of heparin therapy which presents various thromboembolic events associated with high mortality and morbidity. There have been few reports about the prevalence of HIT in acute ischemic stroke, which our retrospective study and a multi-center prospective cohort study respectively estimated as 0.5% and 1.7% of unfractionated heparin-treated acute ischemic stroke patients. Once the onset of HIT is suspected, its therapy should be started immediately because treatment delay of HIT will bring a poor outcome. Stroke physicians should be aware of HIT, as heparin use will become increased more than ever in clinical practice with the development of new intravascular treatment techniques.

Direct thrombin and factor Xa inhibitors in children: a quest for new anticoagulants for children

Venous thrombosis and pulmonary embolism rarely occur in children but are associated with significant morbidity and mortality. Venous thromboembolism (VTE) mostly affects children with severe underlying conditions and multiple risk factors. Newborns and adolescents are at the highest risk. Standard and low molecular weight heparins and vitamin K antagonists are routinely used for the prevention and treatment of VTE. The new anticoagulants, both parenteral such as argatroban, bivalirudin and fondaparinux and oral such as dabigatran and rivaroxaban, have favourable pharmacological properties, all are approved for clinical use in adults and are currently being investigated in children. Argatroban is the only new anticoagulant licensed for use in children so far. The role of these new anticoagulants as alternative anticoagulants for children remains to be defined. This review focuses on the characteristics of VTE in children and reviews current knowledge on the use of the new thrombin and factor Xa inhibitors in this population.

Heparin-induced thrombocytopenia in cardiovascular patients: pathophysiology, diagnosis, and treatment

Heparin-induced thrombocytopenia is a life-threatening immune-mediated platelet activation condition that can cause arterial and venous thromboembolism. The triggering complex, platelet factor 4/heparin antibody, has several unique immunologic characteristics that have not been well elucidated until recently. In patients undergoing cardiovascular procedures such as percutaneous coronary intervention and coronary artery bypass graft surgery, the prevalence of platelet factor 4/heparin antibody is significantly higher than that in the general population. The acuity and graveness of the thromboembolic phenomenon requires early diagnosis and empirical initiation of treatment, even before confirmatory test results are available. Also, although multiple therapeutic modalities exist, the safety and efficacy of each option depends upon the clinical setting. Therefore, this review will focus on the updated pathophysiology of heparin-induced thrombocytopenia, new diagnostic criteria, and the various treatment options for cardiovascular patients with different conditions.

A diagnosis of heparin-induced thrombocytopenia with combined clinical and laboratory methods in cardiothoracic surgical intensive care unit patients

BACKGROUND

Diagnosing postoperative heparin-induced thrombocytopenia (HIT) in cardiothoracic surgical patients is complicated because of the profound thrombocytopenia that occurs with cardiopulmonary bypass (CPB). CPB predisposes patients to develop a frequent incidence of antibodies directed against platelet factor 4 (PF4)/heparin complexes and HIT. The sensitivity of readily available antibody immunoassays is high, but specificity is quite low. The use of both a clinical probability score and rapid laboratory immunoassay has been shown to increase specificity, which is of particular importance in the CPB setting. Prompt diagnosis is crucial because cessation of heparin and treatment with alternative anticoagulation can reduce the risk of thromboembolic events.

METHODS

We retrospectively reviewed records from cardiothoracic surgical patients whose serum was tested with both the serotonin release assay (SRA) and the PF4/heparin immunoassay from January 2007 through December 2010. We assigned a high, intermediate, or low clinical "4Ts" probability score that quantifies thrombocytopenia, timing of platelet decrease, and thrombotic complications in each patient. We then compared the clinical score and the PF4/heparin immunoassay against the "gold standard" diagnostic test, the SRA.

RESULTS

The sensitivity and specificity for PF4/heparin optical density >0.40 were 100% and 26%, respectively. Sensitivity and specificity for the diagnosis of HIT with a combination of PF4/heparin optical density >0.40 and high/intermediate 4Ts score were 100% and 70%, respectively. The negative predictive value was 100% for low 4Ts score.

CONCLUSIONS

We demonstrated that the use of the 4Ts clinical score combined with the PF4/heparin immunoassay for HIT diagnosis increases the sensitivity and specificity of HIT testing compared with the PF4/heparin immunoassay alone. Furthermore, with an intermediate 4Ts score and positive PF4/heparin antibody test, a confirmatory platelet activation assay such as the SRA is necessary. Physicians treating patients after cardiothoracic surgery should recognize the need for an antibody test and confirmation with a platelet activation assay with even moderate clinical probability of HIT.

Application, tolerance and safety of fondaparinux therapy in a German hospital: a prospective single-centre experience

INTRODUCTION

The pentasaccharide fondaparinux is widely approved for prophylaxis and treatment of thromboembolic diseases and therapy of acute coronary syndrome. It is also used off-label in patients with acute, suspected or antecedent heparin-induced thrombocytopenia (HIT). The aim of this prospective observational cohort study was to document fondaparinux' prescription practice, tolerance and therapy safety in a representative mixed German single-centre patient cohort.

PATIENTS AND METHODS

Between 09/2008 - 04/2009, 231 consecutive patients treated with fondaparinux were enrolled. Medical data were obtained from patient's records. The patients were clinically screened for thrombosis (Wells score), sequelae of HIT (4T's score), and bleeding complications (ISTH-criteria) and subjected to further assessment (i.e. sonography, HIT-diagnostics), if necessary. The mortality rate was assessed 30 days after therapy start.

RESULTS

Overall, 153/231 patients had a prophylactic, 74/231 patients a therapeutic, and 4/231 patients a successive prophylactic/therapeutic indication. In 11/231 patients fondaparinux was used due to suspected/antecedent HIT, in 5/231 patients due to a previous cutaneous delayed-type hypersensitivity to heparins. Other indications were rare. Three new/progressive thromboses were detected. No cases of HIT, major bleedings, or fatalities occurred.

CONCLUSIONS

Fondaparinux was well tolerated and was safe in prophylaxis and therapy; prescriptions mostly followed the current approval guidelines and were rarely related to HIT-associated indications (<5% of prescriptions), which is in contrast to previous study results in the U.S. (>94% of prescriptions were HIT-associated). A trend towards an individualised fondaparinux use based on the compound's inherent properties and the patients' risk profiles, i.e., antecedent HIT, bone fractures, heparin allergy, was observed.

Argatroban therapy in pediatric patients requiring nonheparin anticoagulation: an open-label, safety, efficacy, and pharmacokinetic study

BACKGROUND

An increasing number of pediatric patients suffer from thrombotic events necessitating anticoagulation therapy including heparins. Some such patients develop heparin-induced thrombocytopenia (HIT) and thus require alternative anticoagulation. As such, studies evaluating the safety, efficacy, and dosing of alternative anticoagulants are required.

PROCEDURE

In this multicenter, single arm, open-label study, 18 patients ≤ 16 years old received argatroban for either a suspicion of or being at risk for HIT, or other conditions requiring nonheparin anticoagulation. Endpoints included thrombosis, thromboembolic complications, and bleeding.

RESULTS

Patients (ages, 1.6 weeks to 16 years) received argatroban usually for continuous anticoagulation (n = 13) or cardiac catheterization (n = 4). One catheterization patient received a 250 µg/kg bolus only; 17 patients received argatroban continuous infusion (median (range)) 1.1 (0.3-12) µg/kg/min (of whom four received a bolus) for 3.0 (0.1-13.8) days. In patients without bolus dosing, typically argatroban 1 µg/kg/min was initiated, with therapeutic activated partial thromboplastin times (aPTTs) (1.5-3× baseline) achieved within 7 hr. Within 30 days, thrombosis occurred in five patients (two during therapy). No one required amputation or died due to thrombosis during therapy. Two patients had major bleeding. Pharmacometric analyses demonstrated the optimal initial argatroban dose to be 0.75 µg/kg/min (if normal hepatic function), with dose reduction necessary in hepatic impairment.

CONCLUSIONS

In pediatric patients requiring nonheparin anticoagulation, argatroban rapidly provides adequate levels of anticoagulation and is generally well tolerated. For continuous anticoagulation, argatroban 0.75 µg/kg/min (0.2 µg/kg/min in hepatic impairment), adjusted to achieve therapeutic aPTTs, is recommended.

The impact of the heparin-induced thrombocytopenia (HIT) computerized alert on provider behaviors and patient outcomes

OBJECTIVE

The aim of this study was to measure the effect of an electronic heparin-induced thrombocytopenia (HIT) alert on provider ordering behaviors and on patient outcomes.

MATERIALS AND METHODS

A pop-up alert was created for providers when an individual's platelet values had decreased by 50% or to <100,000/mm(3) in the setting of recent heparin exposure. The authors retrospectively compared inpatients admitted between January 24, 2008 and August 24, 2008 to a control group admitted 1 year prior to the HIT alert. The primary outcome was a change in HIT antibody testing. Secondary outcomes included an assessment of incidence of HIT antibody positivity, percentage of patients started on a direct thrombin inhibitor (DTI), length of stay and overall mortality.

RESULTS

There were 1006 and 1081 patients in the control and intervention groups, respectively. There was a 33% relative increase in HIT antibody test orders (p=0.01), and 33% more of these tests were ordered the first day after the criteria were met when a pop-up alert was given (p=0.03). Heparin was discontinued in 25% more patients in the alerted group (p=0.01), and more direct thrombin inhibitors were ordered for them (p=0.03). The number who tested HIT antibody-positive did not differ, however, between the two groups (p=0.99). The length of stay and mortality were similar in both groups.

CONCLUSIONS

The HIT alert significantly impacted provider behaviors. However, the alert did not result in more cases of HIT being detected or an improvement in overall mortality. Our findings do not support implementation of a computerized HIT alert.

Utility of ELISA optical density values and clinical scores for the diagnosis of and thrombosis prediction in heparin-induced thrombocytopenia

Background

Heparin-induced thrombocytopenia (HIT) is an adverse drug reaction caused by antibodies to the heparin/platelet factor 4 (PF4) complex, resulting in thrombocytopenia and prothrombotic state. HIT diagnosis is challenging and depends on clinical presentation and laboratory tests. We investigated the usefulness of clinical scores and heparin/PF4 ELISA optical density (OD) as a diagnostic marker and thrombosis predictor in HIT.

Methods

We analyzed 92 patients with suspected HIT. The heparin/PF4 antibody was measured using a commercial ELISA kit (GTI, USA). For each patient, the 4 T's score and Chong's score were calculated.

Results

Of the 92 patients, 28 were anti-heparin/PF4-seropositive. The 4 T's score and Chong's score showed good correlation (r=0.874). The 4 T's score and OD values showed good performance for diagnosis of the definite and unlikely HIT groups; however, OD levels showed better sensitivity (93.8%) than the 4 T's score used alone (62.5%). Of the 92 patients, 26 developed thrombosis. The OD values were significantly higher in patients with thrombosis than in those without thrombosis (0.52 vs. 0.22, P<0.001). Patients with high OD values (OD>0.4) had an increased risk of thrombosis (adjusted odds ratio 9.44 [3.35-26.6], P<0.001) and a shorter 250-day thrombosis-free survival (32.1% vs. 54.7%, P=0.012).

Conclusions

ELISA OD values in combination with clinical scoring can improve the diagnosis of and thrombosis prediction in HIT. More attention should be paid to the use of clinical scores and OD values as thrombosis predictors in HIT.

Assessment of the 4Ts pretest clinical scoring system as a predictor of heparin-induced thrombocytopenia

STUDY OBJECTIVE

To evaluate the utility of the 4Ts clinical scoring system as a pretest probability method for the detection of heparin-induced thrombocytopenia (HIT).

DESIGN

Prospective observational study.

SETTING

Medical and surgical inpatients at a tertiary care medical center.

PATIENTS

Eighty consecutive patients with suspicion of HIT who had a polyspecific enzyme-linked immunosorbent assay (ELISA) performed between December 1, 2008, and April 1, 2009, for detection of platelet factor 4 (PF4)-heparin antibodies.

MEASUREMENTS AND MAIN RESULTS

The predictive value of the 4Ts scoring system as determined by using a standard laboratory marker of HIT--the ELISA--and the interrater reliability of the scoring system were assessed. Sixty-seven (84%) of the 80 patients had low clinical probability of HIT based on the calculated 4Ts score. The ELISA result was negative for PF4-heparin antibodies in 74 patients (93%). Based on the results of the ELISA, the negative predictive value of the 4Ts score was 91%. Each 4Ts score was calculated by two independent investigators and adjudicated by a third investigator when necessary. The interrater reliability of the scoring system was fair (Cohen κ coefficient 0.362, 95% confidence interval [CI] 0.222-0.502; weighted κ coefficient 0.554 (95% CI 0.441-0.667). Determination of the timing of HIT was associated with the largest number of discrepancies (16) between evaluators, followed by other causes of thrombocytopenia (15), degree of decline in platelet count (14), and the presence of thrombosis or other sequelae (2).

CONCLUSION

A low 4Ts score supports a low probability of HIT based on the results of the polyspecific ELISA. Overall, the interrater reliability of the scoring system was fair. Components of the 4Ts scoring system need to be further clarified or modified in order to improve interrater reliability and thereby increase the clinical utility of this pretest probability model.

Have You Been HIT?

This review is specifically designed to aid the vascular surgeon in the management of heparin-induced thrombocytopenia (HIT). Heparin-induced thrombocytopenia is a rare complication of heparin administration, which poses significant morbidity and mortality. Its onset is usually 5 to 10 days after the heparin administration and should be suspected if platelet counts drop by at least 50%. Confirmation is given by the presence of HIT antibodies on an enzyme-linked immunosorbent assay (ELISA) or in functional platelet activation assays. The major complication is thrombosis and surprisingly bleeding is rare. Heparin must be stopped immediately if there is a clinical suspicion of HIT and alternative anticoagulation must be started. Anticoagulation is required for at least 2 to 3 months to prevent recurrence of thrombosis. Oral anticoagulation with warfarin should not be initiated until the platelet count has been recovered and there should be an overlap of at least 5 days between starting warfarin and stopping the alternative anticoagulant.