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

Successful preemptive renal retransplantation in a patient with previous acute graft loss secondary to HIT type II: a case report and review of literature

Type II heparin-induced thrombocytopenia (HIT II) is an immune-mediated reaction to heparin administration associated with thrombocytopenia and thrombotic complication with potentially serious outcome. We report a case of a 50-year-old man with history of autosomal dominant polycystic kidney disease (ADPKD), homocystinemia, and history of deep vein thrombosis (DVT), who was switched to intravenous heparin from oral coumadin preoperatively in preparation for preemptive living related renal transplant. Following the operation heparin-induced thrombocytopenia type II lead to graft renal artery thrombosis and subsequent graft loss. One year after first transplant patient underwent successful second living unrelated kidney transplantation with no complications with continued anticoagulation with coumadin and with no reexposure to heparin. Two years after the second transplant and 1 year after stopping anticoagulation, patient was readmitted with bilateral lower extremity DVT and high probability of pulmonary embolism. He was given argatroban on admission as a bridge to anticoagulation with lifelong coumadin therapy and is doing well with excellent graft function. To our knowledge, this is the third reported case of HIT in renal transplantation, second reported case associated with graft loss secondary to HIT and the first reported case of successful retransplantation after initial HIT with graft loss. Heparin-induced thrombocytopenia in transplantation can lead to catastrophic consequences in organ recipients. Successful management of this condition emphasizes promptness of diagnosis and treatment and complete cessation of heparin exposure.

Prevalence and risk of preexisting heparin-induced thrombocytopenia antibodies in patients with acute VTE

BACKGROUND

Some patients with acute VTE who may previously have been exposed to heparin products have unrecognized antibodies implicated in heparin-induced thrombocytopenia (HIT). Antibody prevalence and patient consequences upon exposure to heparin, low-molecular-weight heparin, and fondaparinux are uncertain.

METHODS

In this secondary analysis, we tested patients in the Matisse VTE studies at study entry for heparin-dependent antibodies and further tested patients with enzyme-linked immunosorbent assay (ELISA)-positive results for platelet-activating antibodies. We compared the risk of HIT (> 50% fall in platelet count, heparin-dependent antibodies, no contradicting features) between patients treated with heparin (either unfractionated or low molecular weight [enoxaparin]) vs those who received fondaparinux. Comparison groups for thrombocytopenia occurrence comprised patients with ELISA-positive, platelet-activating, antibody-positive results; ELISA-positive, but platelet-activating antibody-negative results; and randomly selected antibody-negative results.

RESULTS

A total of 127 of 3,994 patients (3.2%) had ELISA-positive results at baseline, but only 14 (0.4%; 95% CI, 0.2%-0.6%) had platelet-activating antibodies. Among these 14, four treated with unfractionated or low-molecular-weight heparin developed HIT compared with zero of 10 fondaparinux-treated patients (OR, 95; 95% CI, 8-1,123; P < .001). This frequency (four of four, 100%) significantly differed from that of both heparin-treated patients whose results were ELISA positive but platelet-activating antibody negative and from heparin-treated antibody-negative control subjects (zero of 15 and zero of 27, respectively; P < .001 for both).

CONCLUSIONS

Of patients with VTE, 0.4% had pathologic platelet-activating heparin-dependent antibodies rather than the 3.2% detected by the recommended cutoff of the commercial ELISA. Among study patients with acute VTE who had platelet-activating antibodies, treatment with fondaparinux reduced the risk of precipitating rapid-onset HIT.

[Heparin-induced thrombocytopenia]

Heparin-induced thrombocytopenia (HIT) is an adverse drug reaction that carries an increased risk of thromboembolic complications. HIT is caused by platelet-activating antibodies directed against a complex of platelet factor 4 (PF4) and heparin. HIT typically manifests in the second week after initiation of heparin therapy with a platelet count reduction of more than 50% of the highest level after the start of heparin administration as well as thromboembolic events. The clinical probability can be calculated by the 4 T's score. The laboratory diagnosis of HIT is based on confirmation of PF4/heparin antibodies or on functional tests that provide evidence of heparin-dependent platelet-activating antibodies. A low 4 T's score and negative HIT test virtually rule out the presence of HIT. Patients with acute HIT require anticoagulation with a compatible anticoagulant in a therapeutic dose. The drugs currently available for this include the direct thrombin inhibitors argatroban, lepirudin, bivalirudin, and desirudin and the indirect factor Xa inhibitors danaparoid and fondaparinux.

Venous limb gangrene and fatal hemorrhage: adverse consequences of HIT "overdiagnosis" in a patient with antiphospholipid syndrome

This unfortunate patient case highlights the problems with "overdiagnosis" of HIT. Despite "positive" tests for HIT antibodies, the low pretest probability for HIT and the known propensity of patients with APS to yield false-positive HIT antibody results suggests that the patient did not have a true diagnosis of HIT. Moreover, the early administration of warfarin and the choice of argatroban for parenteral anticoagulation when monitoring was hindered by a prolonged baseline aPTT likely play a key factor in the progression of UE DVT to VLG. Ironically, the problems of anticoagulant monitoring posed by the prolonged baseline aPTT likely contributed to the subsequent overanticoagulation and fatal pulmonary hemorrhage. With benefit of hindsight, avoiding the temptation to test for HIT in a low pretest probability situation, and treatment with either heparin using anti-factor Xa monitoring or with non-aPTT-monitored therapy such as LMWH or fondaparinux would likely have resulted in a more favorable clinical course.

Performance characteristics of two commercially available IgG-specific immunoassays in the assessment of heparin-induced thrombocytopenia (HIT)

BACKGROUND

The in vitro demonstration of antibodies against platelet factor-4/heparin (PF4/hep) complexes is an important contribution to the diagnosis of heparin-induced thrombocytopenia (HIT). The use of PF4/hep IgG-specific immunoassays enhances the specificity of HIT-investigations without any impairment of the sensitivity. Several IgG-specific immunoassays with different origin and structure of the target antigen-complex are commercially available.

METHODS

Using a retrospective cohort consisting of 459 patients suspected to have HIT, we compared the performance characteristics of two commercially available IgG-specific immunoassays, GTI- (Genetic Testing Institute) and HIA-IgG-ELISA (Hyphen Biomed Research).

RESULTS

PF4/hep antibodies were detected in 85 and 81 sera using GTI- and HIA-IgG-ELISA, respectively. OD values and clinical likelihood of patients who tested positive in one assay only were significantly lower than in those who tested positive in both immunoassays. Both IgG-specific assays showed high negative predictive values (100%) and similar but unsatisfactory positive predictive values, determined by a minimum clinical score of 5 and a positive HIPA result (41% and 43%, respectively). The implementation of a confirmatory step using excessive heparin increased the PPV of both assays, but results in a reduction of NPV in HIA-IgG-ELISA.

CONCLUSIONS

The detection of IgG antibodies alone improves the clinical usefulness of immunoassays. However, functional assays remain indispensable to avoid the overdiagnosis of HIT caused by the detection of IgG non-platelet activating antibodies. The OD value in IgG immunoassays appears to correlate with the clinical relevance of the antibodies and might be used as a predictive parameter in the assessment of HIT.

Strategies in heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is an uncommon condition that may confront cardio-thoracic surgeons with difficult problems. The underlying cause of HIT is the formation of antibodies against platelet factor 4/heparin complexes, leading to platelet activation and intravascular platelet aggregation. HIT occurs following heparin administration usually with a time delay of 5-10 days. Clinical suspicion and laboratory tests for platelet-activating antibodies are the cornerstone of diagnosis. Appropriate strategies in HIT are stopping heparin and use of alternative anticoagulants. In addition, surgery with extracorporeal circulation (ECC) should be postponed whenever possible or alternative anticoagulants have to be used during ECC.

How I diagnose and manage HIT

Heparin-induced thrombocytopenia (HIT) is a prothrombotic drug reaction caused by platelet-activating IgG antibodies that recognize platelet factor 4 (PF4)/polyanion complexes. Platelet activation assays, such as the serotonin-release assay, are superior to PF4-dependent immunoassays in discerning which heparin-induced antibodies are clinically relevant. When HIT is strongly suspected, standard practice includes substituting heparin with an alternative anticoagulant; the 2 US-approved agents are the direct thrombin inhibitors (DTIs) lepirudin and argatroban, which are "niche" agents used only to manage HIT. However, only ~ 10% of patients who undergo serological investigation for HIT actually have this diagnosis. Indeed, depending on the clinical setting, only 10%-50% of patients with positive PF4-dependent immunoassays have platelet-activating antibodies. Therefore, overdiagnosis of HIT can be minimized by insisting that a positive platelet activation assay be required for definitive diagnosis of HIT. For these reasons, a management strategy that considers the real possibility of non-HIT thrombocytopenia is warranted. One approach that I suggest is to administer an indirect, antithrombin (AT)-dependent factor Xa inhibitor (danaparoid or fondaparinux) based upon the following rationale: (1) effectiveness in treating and preventing HIT-associated thrombosis; (2) effectiveness in treating and preventing thrombosis in diverse non-HIT situations; (3) both prophylactic- and therapeutic-dose protocols exist, permitting dosing appropriate for the clinical situation; (4) body weight-adjusted dosing protocols and availability of specific anti-factor Xa monitoring reduce risk of under- or overdosing (as can occur with partial thromboplastin time [PTT]-adjusted DTI therapy); (5) their long half-lives reduce risk of rebound hypercoagulability; (6) easy coumarin overlap; and (7) relatively low cost.

The HIT Expert Probability (HEP) Score: a novel pre-test probability model for heparin-induced thrombocytopenia based on broad expert opinion

BACKGROUND

The diagnosis of heparin-induced thrombocytopenia (HIT) is challenging. Over-diagnosis and over-treatment are common.

OBJECTIVES

To develop a pre-test clinical scoring model for HIT based on broad expert opinion that may be useful in guiding clinical decisions regarding therapy.

PATIENTS/METHODS

A pre-test model, the HIT Expert Probability (HEP) Score, was constructed based on the opinions of 26 HIT experts. Fifty patients referred to a reference laboratory for HIT testing comprised the validation cohort. Two hematology trainees scored each patient using the HEP Score and a previously published clinical scoring system (4 T's). A panel of three independent experts adjudicated the 50 patients and rendered a diagnosis of HIT likely or unlikely. All subjects underwent HIT laboratory testing with a polyspecific HIT ELISA and serotonin release assay (SRA).

RESULTS

The HEP Score exhibited significantly greater interobserver agreement [intraclass correlation coefficient: 0.88 (95% CI 0.80-0.93) vs. 0.71 (0.54-0.83)], correlation with the results of HIT laboratory testing and concordance with the diagnosis of the expert panel (area under receiver-operating curve: 0.91 vs. 0.74, P = 0.017) than the 4 T's. The model was 100% sensitive and 60% specific for determining the presence of HIT as defined by the expert panel and would have allowed for a 41% reduction in the number of patients receiving a direct thrombin inhibitor (DTI).

CONCLUSION

The HEP Score is the first pre-test clinical scoring model for HIT based on broad expert opinion, exhibited favorable operating characteristics and may permit clinicians to confidently reduce use of alternative anticoagulants. Prospective multicenter validation is warranted.

Laboratory methods and management of patients with heparin-induced thrombocytopenia

The clinical effects of heparin are meritorious and heparin remains the anticoagulant of choice for most clinical needs. However, as with any drug, adverse effects exist. Heparin-induced thrombocytopenia (HIT) is an important adverse effect of heparin associated with amputation and death due to thrombosis. Although the diagnosis and treatment of HIT can be difficult and complex, it is critical that patients with HIT be identified as soon as possible to initiate early treatment to avoid thrombosis.

Low allergenic potential with fondaparinux: results of a prospective investigation

OBJECTIVE

To determine the incidence and causes of skin reactions to the synthetic pentasaccharide fondaparinux.

PATIENTS AND METHODS

Patients who received prophylactic/therapeutic subcutaneous fondaparinux treatment for more than 7 days were prospectively examined for cutaneous adverse effects between September 1, 2008, and April 30, 2009. When indicated, other procedures, such as skin biopsy, allergy testing, and clinical/laboratory assessment for thrombosis and heparin-induced thrombocytopenia, were performed.

RESULTS

Overall, 231 patients were enrolled. No patient developed typical delayed type IV hypersensitivity (DTH) erythematous skin lesions. However, one female patient experienced abdominal pruritus at sites of injection. Histology revealed a mild lymphohistiocytic infiltrate, confirming a DTH reaction. Heparin-induced thrombocytopenia, as another possible underlying pathomechanism for cutaneous lesions, was ruled out clinically and serologically. Hence, the overall incidence of fondaparinux-induced allergic skin lesions was 0.4% (95% confidence interval, 0.01%-2.4%). No cross-allergies were observed in patients with DTH reaction to heparins.

CONCLUSION

Fondaparinux has a low allergenic potential. The incidence of allergic cutaneous DTH reactions is almost 20 times lower compared to that with commonly used heparins. These results, together with the known low prevalence of secondary thrombotic events or heparin-induced thrombocytopenia during fondaparinux therapy, suggest that in selected patients fondaparinux might substantially improve patient care, therapeutic safety, and cost-effectiveness of anticoagulant therapy.

TRIAL REGISTRATION

clinicaltrials.gov identifier: NCT00510432.

Case report: pediatric liver retransplantation on an extracorporeal membrane oxygenation-dependent child

We describe the perioperative management of a venovenous extracorporeal membrane oxygenator-dependent child requiring liver retransplantation after emergent hepatectomy because of an ischemic liver graft. This child required renal replacement and inotropic support as well as treatment for heparin-induced thrombocytopenia (HIT). We describe each step in this child's perioperative management leading to the successful liver retransplantation. This is the first description, to our knowledge, of a pediatric patient undergoing liver transplantation while supported by extracorporeal membrane oxygenation (ECMO).

Heparin-induced thrombocytopenia: current status and diagnostic challenges

Heparin-induced thrombocytopenia (HIT) is a fairly common and potentially catastrophic complication of heparin therapy. Diagnosing HIT remains a challenge, as the patients at risk often have other reasons for thrombocytopenia and/or thrombosis. HIT is considered a clinicopathologic disorder whose diagnosis is generally made on the basis of both clinical criteria and the presence of "HIT antibodies" in the patient's serum or plasma. There are two basic laboratory approaches to detect HIT antibodies. The immunoassays detect antibodies based on their binding properties, whereas the functional assays detect antibodies based on their platelet-activating properties. Prompt and accurate diagnosis of HIT is imperative, as overdiagnosis exposes patients to alternative anticoagulants and their associated bleeding risks, whereas under- or delayed diagnosis leaves patients vulnerable to the thromboembolic sequelae of HIT, which can be life threatening. A critical interpretation of laboratory results by the clinician is an essential component of diagnosing HIT. This requires a keen understanding of the current concepts in the pathophysiologic mechanisms of the disease, and the application of these concepts when interpreting the results of both the functional and immunoassays. Equally important is an awareness of the strengths and weaknesses, as well as the current lack of standardization and proficiency testing, of these assays.

Heparin-induced non-necrotizing skin lesions: rarely associated with heparin-induced thrombocytopenia

SUMMARY BACKGROUND

Recently, there has been an increasing number of reports regarding adverse skin reactions to subcutaneous heparin administration. Case series have implied that heparin-induced skin lesions are predominantly associated with life-threatening heparin-induced thrombocytopenia (HIT) in at least 22% of patients. Skin lesions, therefore, have been included in clinical scores for HIT.

OBJECTIVES

To determine the association of heparin-induced skin lesions with HIT. This would have a pivotal impact on further anticoagulatory management in patients with heparin-induced skin lesions.

PATIENTS/METHODS

In our observational cohort study, 87 consecutive patients with heparin-induced skin lesions (85 occurring during low-molecular-weight heparin administration) were evaluated using a standardized internal protocol, including HIT diagnostics (heparin-platelet factor 4-ELISA, heparin-induced platelet activation assay), platelet count monitoring, clinical/sonographical screening for thrombosis, skin allergy testing and, if necessary, histology.

RESULTS

None of the observed heparin-induced skin lesions was due to HIT; all lesions were caused by delayed-type IV-hypersensitivity reactions (DTH) instead. Even the cutaneous reaction in one patient with concomitant HIT could be classified histologically as DTH reaction, amounting to an association of heparin-induced skin lesions and HIT in 1.2% (1/87; 95% confidence interval, 0.00-0.06).

CONCLUSION

Heparin-induced skin lesions associated with use of low-molecular-weight heparins do not seem to be strongly associated with a systemic immunologic reaction in terms of HIT and might rather be due to DTH reactions than due to microvascular thrombosis. Hence, we propose refining existing pretest probability scores for HIT, unless underlying causes have been clarified.

Heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is an immune-mediated hypercoagulable disorder caused by antibodies to platelet factor 4 (PF4) and heparin. HIT develops in temporal association with heparin therapy and manifests either as an unexplained thrombocytopenia or thrombocytopenia complicated by thrombosis. The propensity for thrombosis distinguishes HIT from other common drug-induced thrombocytopenias. Diagnosing HIT in hospitalized patients is often challenging because of the frequency of heparin use, occurrence of thrombocytopenia from other causes, and development of asymptomatic PF4/heparin antibodies in patients treated with heparin. This review summarizes our current understanding of the pathogenesis, clinical features, diagnostic criteria, and management approaches in HIT.

Hematological issues in critically ill patients with cancer

Patients with solid and hematologic malignancies presenting with major bleeding or thrombotic complications, potentially life-ending events in a cancer patient's clinical course, usually require admission to an intensive care unit (ICU), making their diagnosis and management even more important for the intensivist. Given the significant advances in the diagnosis and treatment of almost all types of cancers in recent years, the intensivist is likely to encounter an ever-increasing number of cancer patients in the ICU setting with these complications. Abnormal hemostasis can occur as a consequence of both the pathology and treatment of cancer. Because cancer can have multiple effects on hemostatic equilibrium, treatment of these complications can be more complex than in the general population. This article reviews the physiology of coagulation and fibrinolysis, with special attention to those aspects that are most frequently altered in the setting of malignancy. The pathophysiology of bleeding and thrombotic complications specific to critically ill cancer patients are then detailed, and the diagnostic and therapeutic strategies are discussed. Special emphasis is placed on new cancer medications that have an effect on hemostasis, and on novel clotting and anticoagulant agents that are available to the intensivist for the management of these patients.

Heparin-induced thrombocytopenia in surgical patients

BACKGROUND

Unfractionated and low-molecular-weight heparin are commonly used in the prevention and therapy of a variety of cardiovascular diseases. Because the major side effects of these drugs are hemorrhagic events, very little attention is paid to another important side effect (ie, heparin-induced thrombocytopenia [HIT]). HIT is an immune-mediated transient prothrombotic state with very severe implications determined by thromboembolic phenomena in both the venous and arterial circulation.

DATA SOURCES

A PubMed search from 1995 to 2008 was performed. Pertinent literature was identified and other references retrieved from bibliographic citations of the articles identified on PubMed. Articles related to the pathogenesis, clinical picture, diagnosis and treatment of HIT were reviewed.

CONCLUSIONS

HIT is a potentially fatal but treatable and largely preventable disease. An increased awareness of the signs and symptoms of the disorder is necessary to prevent its potentially devastating complications.

The 4Ts scoring system for heparin-induced thrombocytopenia in medical-surgical intensive care unit patients

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is commonly considered but rarely confirmed in critically ill patients. The 4Ts score (Thrombocytopenia, Timing of thrombocytopenia, Thrombosis, and oTher reason) might identify individual patients at risk of having this disorder.

OBJECTIVE

The aim of the study was to evaluate the value of the 4Ts HIT score in comparison with the serotonin-release assay (SRA) in critically ill patients.

METHODS

This study describes the combined results of 3 prospective studies enrolling critically ill patients who were investigated for HIT if platelets fell to less than 50 x 10(9)/L or if platelet counts decreased to less than 50% of the value upon intensive care unit admission. We confirmed HIT by a positive platelet SRA. We assigned a 4Ts score blinded to SRA results to all 50 patients investigated for HIT; those with positive SRA results were scored in duplicate.

RESULTS

Of 528 patients, 50 (9.5%) were investigated for HIT; 39 (78%) of 50 (64%-88%) of these patients were scored as "low probability" by 4Ts score and none had a positive SRA. Of 49 patients who underwent SRA testing because of thrombocytopenia, only 2 (4.1%; 0.5-14.0) had a positive SRA (1 with a moderate 4Ts score and 1 with a high 4Ts score). Therefore, the overall incidence of HIT confirmed by SRA was 2 (0.4%) of 528 (0.04%-1.4%).

CONCLUSIONS

Significant thrombocytopenia during heparin administration occurred in 9.5% of critically ill patients, but HIT was confirmed in only 4.1% of those undergoing testing, for an overall incidence of 0.4%. A low 4Ts score occurred in 78% of patients investigated for HIT; none of these patients had a positive SRA. We conclude that HIT is uncommon in critically ill patients and that the 4Ts score is worthy of further evaluation in this patient population.

Whole blood impedance aggregometry detects heparin-induced thrombocytopenia antibodies

Heparin-induced thrombocytopenia (HIT) is a serious complication of heparin use. IgG antibodies to complexes of platelet factor 4 (PF4) and heparin trigger the clinical manifestations of HIT. Only a subset of these antibodies will activate platelets and these can only be identified with platelet aggregation (functional) assays. Heparin-induced platelet aggregation (HIPA) and (14)C-serotonin release (SRA) assays for HIT are time-consuming and complex to perform. We have developed a whole blood impedance (WBI) test using the new Multiplate analyser. All samples referred to our laboratory over a 10 month period were screened for heparin-PF4 antibodies by an ELISA method (Zymutest HIA IgG). The 4T's score was used to assess HIT pretest probability. Twenty antibody positive samples were further tested by all three functional assays: light transmission aggregometry (LTA), SRA and WBI. Thirteen out of twenty samples were positive by LTA (10 patients) and 15 by WBI (11 patients). SRA, considered to be the gold standard, was used as a confirmatory test and 11 were found to be positive (10 patients); four discrepant samples were weakly positive by WBI. The prevalence of a positive functional test was strongly correlated with the 4T's clinical risk score, but a small number of low-risk patients had positive functional assays. In this study, the WBI assay detected all SRA positive patients and was positive for two others suggesting greater sensitivity. The rapid and easy to perform assay may be a useful tool for haematology laboratories to detect platelet-activating HIT antibodies.

Heparin-Induced Thrombocytopenia in the Intensive Care Unit

Heparin-induced thrombocytopenia (HIT) occurs following an immune reaction to the administration of heparin, which results in increased platelet activation and thrombocytopenia, and lead to arterial and venous thrombosis in untreated cases. It may be considered as an idiosyncratic, drug-induced reaction in which heparin injections result in the formation of complexes with platelet factor 4 (PF4), triggering an antibody-mediated reaction in certain individuals. Low platelet count in this instance is secondary to platelet aggregation and can lead to thrombotic complications by vascular occlusion and other mechanisms. Early recognition of this complication is essential to prevent life- and limb-threatening thrombosis. Therefore, it is important that intensive care physicians who administer heparin in different forms are aware of this potential adverse event and follow a regular plan in monitoring the platelet count while the patient is on heparin. In a patient whose platelet count falls while on heparin, when no other diagnostic possibilities can easily explain it, immediate withdrawal of any form of heparin and commencement of an alternative anticoagulant is necessary until the diagnosis of HIT is confirmed or excluded. At the same time, it is important that over-diagnosis of HIT is not made to avoid unwanted bleeding complications from the alternative anticoagulants. This review outlines the pathophysiology, diagnosis and management of HIT with a focus on the intensive care setting.

Early-onset and persisting thrombocytopenia in post-cardiac surgery patients is rarely due to heparin-induced thrombocytopenia, even when antibody tests are positive

BACKGROUND

The high frequency of thrombocytopenia in post-cardiac surgery patients makes it challenging to diagnose heparin-induced thrombocytopenia (HIT). Two platelet count profiles are reported as indicating possible HIT in these patients: profile 1 describes a platelet count fall that begins between postoperative days 5 and 10, whereas profile 2 denotes early-onset thrombocytopenia that persists beyond day 5.

OBJECTIVES

To examine how these platelet count profiles correlate with antibody status and HIT post-cardiac surgery.

METHODS

We prospectively screened 581 cardiac surgery patients for heparin-dependent antibodies by platelet factor 4 (PF4)-heparin immunoassay and platelet-activation test, and performed daily platelet counts (until day 10) with 30-day follow-up.

RESULTS

All three patients with platelet count profile 1 tested positive for platelet-activating anti-PF4-heparin IgG antibodies [odds ratio (OR) 521.7, 95% confidence interval (CI) 3.9-34,000, P = 0.002], and were judged to have HIT. In contrast, none of 25 patients with early-onset and persisting thrombocytopenia (profile 2) was judged to have HIT, including five patients testing positive for platelet-activating anti-PF4-heparin IgG antibodies. In these patients, the frequency of heparin-dependent antibodies did not differ from that in non-thrombocytopenic controls, either for anti-PF4-heparin IgG (OR 1.7, 95% CI 0.7-4.1, P = 0.31) or for platelet-activating antibodies (OR 1.9, 95% CI 0.6-5.7, P = 0.20). Multivariate analysis revealed that type of cardiac surgery, but not HIT antibody status, predicted early-onset and persisting thrombocytopenia. Together, these findings show that HIT was uncommon in this study population [overall frequency, 3/581 (0.5%), 95% CI 0.1-1.5%].

CONCLUSIONS

Thrombocytopenia that begins between 5 and 10 days post-cardiac surgery is highly predictive for HIT. In contrast, early-onset and persisting thrombocytopenia is usually caused by non-HIT factors with coinciding heparin-dependent antibody seroconversion.

Cerebral sinus thrombosis and heparin-induced thrombocytopenia in a patient with paroxysmal nocturnal hemoglobinuria

Paroxysmal nocturnal hemoglobinuria is a rare acquired disorder of clonal hematopoietic stem cells and it is characterized as a hypercoagulable disorder. We report a 36-year-old woman with the rare triad of paroxysmal nocturnal hemoglobinuria, cerebral sinus thrombosis triggered by infection, and rapid-onset heparin-induced thrombocytopenia after resensitization of heparin. This case raises caution for heparin-induced thrombocytopenia in paroxysmal nocturnal hemoglobinuria.

[Heparin-induced thrombocytopenia occurring after surgical treatment of atrial myxoma--a case report]

INTRODUCTION

Heparin-induced thrombocytopenia (HIT) is an acquired, prothrombotic disorder, caused by antibodies to a complex of heparin and platelet factor 4 (PF4) that activates platelets, resulting in the release of procoagulant microparticles, thrombocytopenia occurrence, generation of thrombin, and frequent thromboses.

CASE OUTLINE

We present a case of severe HIT in a 68-year-old female, which occurred after cardiosurgery of the left atrial myxoma with the aim to point out the importance of differential diagnosis of thrombocytopenia in patients recently exposed to heparin. Platelet count dropped on the eleventh postoperative day, six days after unfractioned heparin and enoxaparine threatment, to 4x10(9)/I.The correct diagnosis failed to be made at first. Since thrombocytopenia remained refractory to a corticosteroid treatment and platelet transfusion, the patient was hospitalized on the 13th postoperative day at the Institute of Haematology. The diagnosis of HIT was confirmed with the high-probability clinical score (4T's) and strongly positive anti-heparin-PF4 (PaGIA) test as well as positive platelet aggregation test. The treatment started with a smaller therapeutic doses of danaparoid than recommended of 750 U intravenous bolus and was followed by continuous infusions of 100 U per 1 h and intravenous gammaglobulins in full dosage for four days. The platelet count started to rise on the third day and it was completely normalized on the 5th day of the therapy.

CONCLUSION

Treatment of severe HIT with small doses of danaparoid supplemented by intravenous gamma globulin was successful. Additional awareness of heparin-induced thrombocytopenia is needed, especially of HIT in differential diagnosis of thrombocytopenia in patients recently exposed to heparin.

The severity of trauma determines the immune response to PF4/heparin and the frequency of heparin-induced thrombocytopenia

Heparin can induce heparin-induced thrombocytopenia (HIT). The combined effect of type of surgery (major vs minor) and heparin on this prothrombotic immune reaction to platelet factor 4 (PF4)/heparin was analyzed. In a randomized, double-blind study, trauma patients receiving low-molecular-weight (LMWH) or unfractionated heparin (UFH) for thrombosis prophylaxis were assessed for PF4/heparin-antibody seroconversion, HIT, and thrombosis according to type of surgery. The risk for seroconversion was higher than major versus minor surgery odds ratio, 7.98 [95% confidence interval, 2.06-31.00], P = .003, controlled for potential confounders, as was the risk for HIT (2.2% [95% confidence interval, 0.3%-4.1%] vs 0.0%, P = .010). During LMWH compared with UFH thromboprophylaxis, HIT (1 of 298 vs 4 of 316; P = .370) and PF4/heparin seroconversion (1.7% vs 6.6%; P = .002) were less frequent, driven by differences in patients undergoing major surgery (incidence of HIT: LMWH 0.8% vs UFH 4.0%; P = .180; seroconversion rates: 4.0% vs 17.0%; P = .001). After minor surgery, no case of HIT occurred. The severity of trauma and the need for major surgery strongly influence the risk of an anti-PF4/heparin immune response, which is then increased by UFH. In major trauma certoparin may be safer than UFH because it induces HIT-antibody seroconversion, and the corresponding risk of HIT, less frequently.

A review of 122 published outcomes of danaparoid anticoagulation for intermittent haemodialysis

One hundred and twenty-two case reports of treatment outcomes of danaparoid use for intermittent haemodialysis (HD) in severely ill patients with heparin intolerance (including 97 HIT patients) have been analysed. HD sessions of 4 - 6 hours were successfully conducted daily to 3 times/week for periods of up to 4 years (median 7 sessions/patient (range 1 - >650). In these patients danaparoid use was relatively safe (4 unprovoked non-fatal major bleeds) and efficacious in protecting the circuit (95% no clotting problem) or patient (6 thromboses: 4 fatal or leading to danaparoid discontinuation). HIT diagnosis was improved if recurrent platelet count reduction with each HD and circuit/AV graft clotting were included. Alternative reasons for and very low nadirs of the platelet count undermined the usefulness of the 4 T pre-test HIT predictability scores, but a positive functional serological test confirmed HIT in most patients. Deaths (15.6%) and thrombosis only occurred in HIT cases. Possible reasons are discussed. Replacing the standard intermittent pre-HD dose regimen with the therapeutic infusion regimen to provide continuous daily systemic antithrombotic protection, should further improve efficacy.

CONCLUSION

Danaparoid appears to be a useful alternative antithrombotic for patients with heparin intolerance and renal failure requiring haemodialysis.

Cardiac transplantation and/or mechanical circulatory support device placement using heparin anti-coagulation in the presence of acute heparin-induced thrombocytopenia

BACKGROUND

Patients with congestive heart failure, decreased left ventricular function, and debilitation are frequently maintained on anti-coagulants, including heparin. As such, these patients are at high risk for developing heparin-induced thrombocytopenia (HIT). Some of these HIT-positive individuals will ultimately undergo urgent heart transplantation or placement of a mechanical circulatory support device (MCSD). Such procedures require cardiopulmonary bypass (CPB) and full anti-coagulation. The safety of re-exposure to heparin during CPB despite the presence of recent-onset thrombocytopenia and Hep/PF4 antibodies has not been studied in the transplant or MCSD populations.

METHODS

Over a 24-month period, 75 heart transplants and 55 MCSD implants were performed. Fourteen patients with acute HIT (thrombocytopenia and positive Hep/PF4 antibody by enzyme-linked immunosorbent assay [ELISA]) and 3 patients with a history of remote HIT underwent cardiac transplantation (n = 9) and/or MCSD placement (n = 8) using heparin as the anti-coagulant during CPB. The median time from diagnosis to CPB was 4.5 days in patients with acute HIT.

RESULTS

Thirty-day survival was 100% in transplant patients and 75% in MCSD patients. Post-transplant ELISA testing was found to be negative in 4 patients with acute HIT and 3 with remote HIT.

CONCLUSIONS

This series demonstrates that short-term re-exposure to heparin during urgent CPB for heart transplantation or MCSD placement is safe despite the presence of thrombocytopenia and Hep/PF4 antibodies. Moreover, the rapid clearance of Hep/PF4 antibodies in our transplant patients suggests a potential therapeutic role for immunosuppressive therapy in the management of HIT in the acute setting.

Variability of anti-PF4/heparin antibody results obtained by the rapid testing system ID-H/PF4-PaGIA

BACKGROUND

Recent studies have shown that a low clinical pretest probability may be adequate for excluding heparin-induced thrombocytopenia. However, for patients with intermediate or high pretest probability, laboratory testing is essential for confirming or refuting the diagnosis. Rapid assessment of anti-PF4/heparin-antibodies may assist clinical decision-making.

OBJECTIVES

To evaluate the performance of rapid ID-H/PF4-PaGIA. In particular, we verified reproducibility of results between plasma and serum specimens, between fresh and frozen samples, and between different ID-H/PF4-polymer lots (polystyrene beads coated with heparin/PF4-complexes).

PATIENTS/METHODS

The samples studied were 1376 plasma and 914 corresponding serum samples from patients investigated for suspected heparin-induced thrombocytopenia between January 2000 and October 2008. Anti-PF4/heparin-antibodies were assessed by ID-H/PF4-PaGIA, commercially available ELISAs and heparin-induced platelet aggregation test.

RESULTS

Among 914 paired plasma/serum samples we noted discordant results (negative vs. low-titre positive) in nine instances (1%; 95%CI, 0.4-1.6%). Overall, agreement between titres assessed in plasma vs. serum was highly significant (Spearman correlation coefficient, 0.975; P < 0.0001). Forty-seven samples tested both fresh and after freezing/thawing showed a good agreement, with one discordant positive/negative result (Spearman correlation coefficient, 0.970; P < 0.0001). Among 1376 plasma samples we noted a strikingly variable incidence of false negative results (none - 82%; 95%CI, 66-98%), depending on the employed ID-H/PF4-polymer lot. Faulty lots can be recognized by titrating commercial positive controls and stored samples of HIT-patients.

CONCLUSION

Laboratories performing the assay should implement stringent internal quality controls in order to recognize potentially faulty ID-H/PF4-polymer lots, thus avoiding false negative results.

Heparin-induced thrombocytopenia with multiple organized thrombi accompanied by unusual cholesterin deposition: autopsy case after long-term follow up

Heparin-induced thrombocytopenia (HIT) is characterized by a reduction in the platelet count and systemic thromboembolism during heparin therapy. Herein is reported a case of HIT with characteristic thrombus formation. A 68-year-old man who had been treated for hypertension for 27 years suffered a brain infarction and was treated with heparin. After this treatment, other new infarctions occurred in multiple organs. Because serum antibodies against heparin/PF4 complex were detected, he was diagnosed as having HIT, and warfarin and argatroban were administered instead of heparin. He died, however, 119 days after the first onset. At autopsy infarction due to organized thrombi with cholesterin deposition in multiple organs were found, similar to usual atherosclerotic emboli, but different to them with regard to clinical course and distribution of thrombi. This case in which organization and frequent cholesterin deposition were found in thromboembolized lesions of multiple organs after relatively long-term follow up, is unusual. The findings suggest that HIT accompanied by marked hypercholesterolemia of long duration contributes to a characteristic form of thromboembolism that needs careful management.

Fondaparinux and the management of heparin-induced thrombocytopenia: the journey continues

OBJECTIVE

To review the available literature addressing the role of fondaparinux in the management of heparin-induced thrombocytopenia (HIT).

DATA SOURCES

Primary articles were identified by a MEDLINE search (2004-June 2009) of English-language literature using the MeSH headings fondaparinux, heparin, low-molecular-weight heparin, and thrombocytopenia. Relevant consensus guidelines (2006-June 2009) were also identified.

STUDY SELECTION AND DATA EXTRACTION

All published studies and case reports, as well as relevant consensus guidelines, evaluating the use of fondaparinux for the management of HIT were included.

DATA SYNTHESIS

The role of fondaparinux in the management of HIT is a therapeutic controversy challenging clinicians today. An open-label, prospective pilot study of 7 patients with acute HIT supports fondaparinux as an alternative anticoagulant. Additionally, a total of 12 patients with HIT from a larger case study and retrospective cohort were successfully treated with fondaparinux. Much of the supporting data exists in the form of case reports, each demonstrating normalization of platelet counts without any evidence of new thrombosis. The differences in clinical scenarios as well as the role and dose of fondaparinux make interpretation of these reports difficult. Three case reports have been published raising concerns regarding fondaparinux causing or failing to manage HIT appropriately. However, common weaknesses such as small sample sizes and nonuniform definitions of HIT limit the usefulness of these findings. The updated American College of Chest Physicians consensus guidelines now recognize fondaparinux as an option in the management of HIT; however, the level of evidence supporting this is of low quality. The use of fondaparinux as a bridging agent between direct thrombin inhibitor and warfarin therapy has been proposed. A recently published case report gives support to this approach.

CONCLUSIONS

Controlled clinical trials evaluating the use of fondaparinux in the management of HIT need to be completed before this therapy can be routinely recommended.

Effect of anti-platelet factor-4/heparin antibody induction on early saphenous vein graft occlusion after coronary artery bypass surgery

BACKGROUND

Antibodies to complexes of heparin and platelet factor 4 (PF4) are capable of causing heparin-induced thrombocytopenia (HIT). Recent evidence suggests that anti-PF4/heparin antibodies may be prothrombogenic even in the absence of thrombocytopenia and clinically-recognized HIT.

OBJECTIVES

To determine if induction of anti-PF4/heparin antibodies is an independent risk factor for early saphenous vein graft (SVG) occlusion or adverse clinical outcome after coronary artery bypass graft (CABG) surgery.

PATIENTS/METHODS

Anti-PF4/heparin antibody titers were measured in 368 patients prior to and then 4 days, 6 weeks and 6 months after CABG surgery. Serotonin release assay (SRA) and antibody isotype analysis were also performed on 6-week samples. SVG patency was determined in 297 patients 6 months after surgery by multidetector computed tomography coronary angiography.

RESULTS

Six weeks after surgery, 52% of patients were anti-PF4/heparin seropositive and 9% were SRA positive. Six months after surgery, neither the percentage of occluded SVG (19% vs. 20%, P = NS), the percentage of patients with an occluded SVG (33% vs. 33%, P = NS) nor the incidence of adverse clinical events (21% vs. 24%, P = NS) differed between seropositive and seronegative groups. Neither IgG isotype nor SRA positivity was additionally predictive of SVG occlusion or adverse clinical outcome.

CONCLUSION

Induction of anti-PF4/heparin antibodies, even those capable of heparin-dependent platelet activation, is not independently associated with early SVG occlusion or adverse clinical outcomes after CABG surgery.