Physiological changes in membrane-expressed platelet factor 4: Implications in heparin-induced thrombocytopenia

Background

Many heparin-induced thrombocytopenia (HIT) antibodies cause platelet activation in the serotonin release assay (SRA) in the absence of heparin. This in vitro observation may help unravel the mechanism of delayed-onset HIT, where seropositive patients develop thrombocytopenia and associated thrombosis after cessation of heparin.

Objective

Studies were conducted to examine the relationship between platelet environment, surface PF4 expression, and the extent of heparin-independent platelet activation in the SRA.

Methods

Ex vivo platelets were washed and labeled for SRA, then used either before or after 45 minutes of recovery at 37 °C. HIT antibody-mediated serotonin release in the absence of heparin was compared to the extent of surface staining of the platelets with fluorescent anti-human PF4 antibodies.

Results

Handling of platelets for in vitro studies resulted in transient expression of surface PF4, and it was during this interval that platelets were most sensitive to activation by HIT antibodies in the absence of heparin. Heparin-independent platelet activation was attenuated when SRA-positive specimens were retested after platelets were incubated 45 minutes at 37 °C. Surface PF4 expression was diminished on the rested platelets, compared to the same platelets labeled immediately after handling. Thus compared to rested platelets, mildly activated platelets had elevated surface PF4 expression and a higher level of HIT antibody-mediated, heparin-independent platelet activation.

Conclusion

Surface expression of PF4 reflects HIT antigen presentation, and varies with the physiological state of platelets. Thus there can be differences in HIT antibody target availability among patients which may explain the variability in consequences of HIT antibody seropositivity.     

A clinical-laboratory approach contributing to a rapid and reliable diagnosis of heparin-induced thrombocytopenia

Introduction

Heparin-induced thrombocytopenia (HIT) remains a very challenging diagnosis. The first objective of this study was to compare the performance of the ID-H/PF4 PaGIA^® with the Asserachrom^® HPIA ELISA. The main purpose was to evaluate the diagnostic utility of the combination of the H/PF4 PaGIA^® with the clinical “4T's” score as a screening strategy.

Materials and Methods

102 patients with clinical suspicion of HIT were classified into risk groups using the 4T's score. The presence of HIT antibodies was assessed by two immunoassays and confirmed by a functional flow cytometric assay.

Results

Comparison of the ID-H/PF4 PaGIA^® with the Asserachrom^® HPIA ELISA demonstrated a comparable technical performance, being an excellent screening test to rule out HIT (negative predictive value or NPV = 100%). According to the 4T's score, HIT was excluded in all low risk patients (NPV = 100%). ELISA optical density levels were significantly different between all risk groups (P-values < 0.01). In contrast, due to the low positive predictive value (22%) and weak positive likelihood ratio (2.6), a positive ID-H/PF4 PaGIA^® result did not considerably increase the probability of HIT.

Conclusion

Our study confirms the combination of the 4T's score with the ID-H/PF4 PaGIA^® as a reliable strategy to rule out HIT. Yet, confirming positive ID-H/PF4 PaGIA^® results by flow cytometry within 1-2 h after blood sampling remains necessary. This novel clinical-laboratory approach can contribute in a rapid and reliable way to the definite diagnosis of HIT.     

Combined use of the high heparin step and optical density to optimize diagnostic sensitivity and specificity of an anti-PF4/heparin enzyme-immunoassay

Background

IgG-specific anti-PF4/heparin enzyme-immunoassays (EIAs) are sensitive but not specific for platelet-activating antibodies, the cause of heparin-induced thrombocytopenia (HIT). Two features of EIA reactivity predict for presence of HIT antibodies - the magnitude of a positive result (in optical density [OD] units) and the inhibition of reactivity at high heparin concentrations - but their combined utility remains uncertain.

Objective

To determine for an IgG-specific EIA how the OD values of a positive reaction and its inhibition by high heparin can be optimally combined.

Methods

We screened 1,000 consecutive patients with suspected HIT using an IgG-specific PF4/heparin in-house EIA with and without high heparin (100 IU/mL); and by the heparin-induced platelet activation test.

Results

Platelet-activating antibodies were rarely detected (< 0.2%) when the IgG-specific EIA was negative at the conventional cut-off (OD, 0.5). However, an OD cut-off of 1.0 resulted in an unacceptable loss of sensitivity (14/83 = 17%) for detecting platelet-activating antibodies. The high heparin step increased specificity for platelet-activating antibodies from 72% to 89% without loss of sensitivity when applied to weak-positive sera (OD ≤ 1.0). However, decreased sensitivity was observed with strong-positive sera (OD > 1.0): 11/69 such sera (16%) that did not show > 40% inhibition by high heparin nevertheless contained platelet-activating antibodies.

Conclusion

Specificity of an IgG-specific EIA for detecting platelet-activating antibodies can be optimized by applying the high heparin inhibition step to weak-positive reactions (0.5- ≤ 1.0 OD). However, applying the high heparin inhibition step to strong-positive reactions (> 1.0 OD) in our in-house assay risks falsely classifying a serum as negative for platelet-activating antibodies.     

Different effects of enoxaparin and unfractionated heparin on some thrombogenesis markers during hemodialysis: a cross-over study

Background

Unfractionated heparin (UFH) and low molecular weight heparin constitute fundamental anticoagulants during hemodialysis (HD). We aimed to investigate the effect of UFH and enoxaparin on plasma levels of prothrombin fragment 1 + 2 (PF 1 + 2) and thrombin/antithrombin complex (TAT) as markers of intravascular thrombogenesis during HD.

Methods

We enrolled 22 chronic HD patients, who were randomly assigned to either iv enoxaparin (n = 11) or UFH (n = 11) anticoagulation, and followed prospectively for 12 weeks before crossing over to the alternate therapy for further 12 weeks. Plasma levels of PF 1 + 2 and TAT were measured by immunoassay at the start, at 10 and 180 min of HD session after each period of evaluation.

Results

The baseline PF 1 + 2 and TAT levels were comparable under enoxaparin and UFH treatment. PF 1 + 2 significantly decreased during both UFH (χ² ANOVA = 9.82, P = 0.007) and enoxaparin (χ² ANOVA = 29.40, P < 10^− 6) anticoagulated HD, while over-HD TAT levels changes differed depending on the type of heparin. The switch from enoxaparin to UFH treatment was connected with a significantly higher PF 1 + 2 after 10 and 180 min as well as higher TAT concentration after 180 min of HD. Only during enoxaparin anticoagulated HD 34% PF 1 + 2 decrease and TAT levels after 180 min of HD was closely associated with heparin dosage.

Conclusion

Single bolus of enoxaparin ensures efficient and convenient anti-thrombotic protection during HD procedure. Enoxaparin mean dose of 0.67 mg/kg, which is generally lower than manufacturer's instructions, can be recommended for over-dialytic regular use.     

Low prevalence of heparin-induced thrombocytopenia after cardiac surgery in Thai patients

Introduction

Heparin induced-thrombocytopenia (HIT) has been well recognized in Western countries. However, there are no data in the Thai population. We therefore investigated the prevalence of anti-platelet factor 4 (PF4)/heparin antibodies, HIT, and its thrombotic complications in Thai patients undergoing cardiac surgery using unfractionated heparin.

Materials and methods

Seventy-three consecutive patients were prospectively enrolled in this study. Blood samples before operation and week 1, week 2, and week 3 after operation were collected from each patient for HIT antibody screening by enzyme-linked immunosorbent assay using IgG antibody specific to the PF4/heparin complex. Positive samples were further analyzed by ¹⁴C-serotonin release assay. Complete blood count was performed daily during the first week, then weekly for 3 weeks.

Results

No patient had detectable anti-PF4/heparin antibodies at baseline. Five patients sero-converted during the course of the study for anti-PF4/heparin IgG: 3 (4.1%) at week 1, 4 (5.5%) at week 2, and 5 (6.8%) at week 3 after surgery. However, none of these patients had anti-PF4/heparin antibodies that resulted in ¹⁴C-serotonin release to be considered clinically significant antibodies. Post-operative thrombocytopenia after the operation was found in 35 patients (47.9%), but was not considered to be caused by HIT. Thromboembolic events occurred in 3 patients (4.1%) during follow up; however, none of these patients had positive PF4/heparin antibody tests.

Conclusions

Our study represents the first study to examine Thai patients exposed to heparin in the context of cardiac surgery. We found a lower prevalence of positive anti-PF4/heparin antibodies and clinical HIT than previously published studies.     

Genome-wide association study of blood pressure response to methylphenidate treatment of attention-deficit/hyperactivity disorder

Objective

We conducted a genome-wide association study of blood pressure in an open-label study of the methylphenidate transdermal system (MTS) for the treatment of attention-deficit/hyperactivity disorder (ADHD).

Method

Genotyping was conducted with the Affymetrix Genome-Wide Human SNP Array 6.0. Multivariate association analyses were conducted using the software package PLINK. After data cleaning and quality control we tested 316,934 SNPs in 140 children with ADHD.

Results

We observed no genome-wide statistically significant findings, but a SNP in a K⁺-dependent Na⁺/Ca²⁺ exchanger expressed in vascular smooth muscle (SLC24A3) was included in our top associations at p < 1E-04. Genetic enrichment analyses of genes with ≥ 1 SNP significant at p < 0.01, implicated several functional categories (FERM domain, p = 5.0E-07; immunoglobulin domain, p = 8.1E-06; the transmembrane region, p = 4.4E-05; channel activity, p = 2.0E-04; and type-III fibronectins, p = 2.7E-05) harboring genes previously associated with related cardiovascular phenotypes.

Conclusions

The hypothesis generating results from this study suggests that polymorphisms in several genes consistently associated with cardiovascular diseases may impact changes in blood pressure observed with methylphenidate pharmacotherapy in children with ADHD.     

New insights in heparin-induced thrombocytopenia by the use of fluid-phase assays to detect specifically platelet factor 4/heparin complex antibodies and antibody-secreting cells

Introduction

The key feature of heparin-induced thrombocytopenia (HIT) is the production of antibodies (Ab) against the platelet factor 4 (PF4)/heparin complex. These Ab are directed against neoepitopes of the PF4 tetramer, which are induced by the complex formation with heparin. To study this humoral immune response in greater detail, either in a murine immunization model or in human blood samples, reliable and specific immune assays to detect specifically Ab against the PF4/heparin complexes, but not PF4 alone are required.

Materials and Methods

We established fluid-phase enzyme-immunoassays in which the soluble biotinylated antigen, PF4/heparin, is firstly captured by specific Ab, and secondly directly detected with enzyme-conjugated streptavidin.

Results

The use of this fluid-phase principle allowed a higher specificity than the traditional solid-phase enzyme-immunoassays in terms of Ab binding to murine PF4/heparin compared to murine PF4 alone. This fluid-phase approach applied to the detection of specific murine PF4/heparin Ab-secreting cells (ASC) identified the spleen as the main lymphatic organ that contributes to the PF4/heparin Ab response in mice. IgG ASC specific for PF4/heparin are very transiently detectable in mice, which might explain why anti-PF4/heparin IgG Ab typically disappear within 100 days in humans. Furthermore, this fluid-phase approach was successfully transferred to detect human PF4/heparin-specific Ab.

Conclusion

The fluid-phase principle for the specific detection of anti-PF4/heparin IgG and IgM Ab enables new and improved assays for HIT research in men and mice. At least in mice PF4/heparin antibodies are produced by transient B cells.     

Enhanced platelet reactivity and thrombosis in Apoe-/- mice exposed to cigarette smoke is attenuated by P2Y12 antagonism

Introduction

Smoking increases the risk of acute arterial thrombosis, including myocardial infarction, likely due to multi-factorial effects on the vasculature. Heightened platelet reactivity may be among the adverse effects of smoke exposure.

Methods

To examine the effects of smoke exposure on platelet function in an atherosclerotic environment, Apoe-deficient female mice, maintained on a Western diet, were exposed (4 hrs/d, 5d/wk) to sidestream cigarette smoke in a whole-body exposure chamber for12 weeks. A separate group of wild type C57BL/6 J mice were also exposed to smoke in an identical fashion.

Results

In comparison to control Apoe-/- mice exposed to filtered ambient air, smoke-exposed Apoe-/- mice displayed a 1.8 ± 0.3 fold enhanced ADP-induced fibrinogen binding ex vivo (P < 0.001) and had a shorter time to thrombotic occlusion following ferric chloride injury of the carotid artery (median time to thrombosis of 8 vs. 13 min; P = 0.015). Administration of the direct-acting P2Y12 antagonist cangrelor blunted ex vivo fibrinogen binding and attenuated thrombosis (median time 20 min) in Apoe-/- mice exposed to sidestream smoke. The effects of smoke exposure required a proatherosclerotic background, as wild-type C57Bl/6 J mice exposed to smoke displayed similar fibrinogen binding and thrombotic occlusion times as did control mice.

Conclusions

Our results demonstrate that exposure to smoke heightens platelet reactivity and thrombosis in Apoe-/- mice and implicate signaling through platelet P2Y12 receptor as a mediator of the adverse consequence of smoke exposure. These results may partially explain the recent observations that smokers derive greater clinical benefit from the P2Y12 antagonist clopidogrel than do non-smokers.     

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.     

Antiplatelet factor 4/heparin antibodies in patients with gram negative bacteremia

Heparin-induced thrombocytopenia (HIT) is an antibody-mediated syndrome of thrombocytopenia and prothrombotic state that follows exposure to heparin. However, spontaneous HIT has been described in the setting of infection, without evidence of previous heparin administration. Since PF4 binds to lipid A portion of lipopolysaccharide, we tested for the presence of antiPF4/heparin antibodies in patients with gram-negative bacteremia. Patients with bacteremia had higher titers of antiPF4/heparin antibodies compared to normal controls 26.3 ± SD 34 units, N = 32 versus 6.3 ± SD 2.38 units, N = 10, P = 0.001. FITC-labeled PF4 interacted with lipopolysaccharide in a concentration-dependent manner as determined by quenching of the emission spectrum following excitation at λ 488. In addition, immunoaffinity purified antiPF4/Heparin antibodies from 3 patients with HIT cross-reacted with PF4/heparin complex. These results show that PF4/LPS complex is immunogenic and can elicit cross-reacting antibodies against PF4/Heparin, providing an explanation for the presence of these antibodies in individuals, who were never been exposed to heparin before. These antibodies may also be at least partly responsible for the thrombocytopenia associated with infection.     

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 4T 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.     

Direct comparison of enoxaparin and nadroparin in a rabbit model of arterial thrombosis prevention

Introduction

The aim of the study was to evaluate and compare the efficacy of standard unfractionated heparin (UFH) and low-molecular weight heparins (LMWH's).

Materials and Methods

We modified a previously published rabbit model of arterial thrombosis prevention [1,2] to compare unfractionated heparin and two different doses of two low-molecular weight heparin fragments - nadroparin and enoxaparin. Thrombosis in the distal aorta was triggered by vessel wall injury and critical stenosis. Blood flow in the damaged arterial segment was monitored by a flow probe placed distal to the constrictor. The primary endpoints of the study were: (1) cumulative flow, (2) time to occlusion and (3) residual clot weight. Thirty six animals were split into 6 groups with six animals in each group. Control groups were given saline or heparin and four more groups were used to compare LMWH's at 2 different doses.

Results

In our study, all treatments were superior to the saline control group (α ≤ 0,01). Standard heparin was inferior (α ≤ 0,05) to both low molecular weight heparins for all primary endpoints (cumulative flow, time to occlusion and residual clot weight). There were no differences between the LMWH's except for cumulative flow at high doses.

Conclusions

This study revealed no relevant differences between nadroparin and enoxaparin for the primary endpoints of our model. Clinical use of each drug remains a personal preference.     

Heparin attenuates lipopolysaccharide-induced acute lung injury by inhibiting nitric oxide synthase and TGF-β/Smad signaling pathway

Introduction

Heparin, a potent blood anticoagulant, has been shown to exert a variety of pharmacological activities. The purpose of this study was to investigate whether heparin has a beneficial effect on lipopolysaccharide (LPS)-induced acute lung injury (ALI) in rats and to further explore the possible underlying mechanisms.

Materials and methods

Adult Sprague-Dawley rats were randomly assigned into the control, heparin, LPS, and LPS plus heparin groups. ALI was induced by intratracheal instillation of LPS at a dose of 1 mg/kg. Rats in the LPS plus heparin group were intravenously received 50 U/ kg heparin every 1 h after the induction of ALI.

Results

We found that heparin significantly improved LPS-induced lung pathological changes, inhibited myeloperoxidase (MPO) activity, and reduced malondialdehyde (MDA) level and lung wet/dry weight ratio. Heparin also inhibited the release of tumor necrosis factor (TNF)-α and interleukin (IL)-6, and markedly decreased the expression of inducible nitric oxide synthase (iNOS) in lung tissues and thus prevented nitric oxide (NO) release in response to LPS challenge. Additionally, heparin decreased the expression of transforming growth factor-β1 (TGF-β1), p-Smad 2, and p-Smad 3, which are all important molecules of the TGF-β1/Smad signaling pathway.

Conclusions

Heparin significantly ameliorated the lung injury induced by LPS in rats via the inhibition of nitric oxide synthase expression and the TGF-β/Smad pathway. Heparin may be a potential therapeutic reagent for treating ALI in the future.     

Pain due to osteoarthritis may impair the early outcome of deep brain stimulation in Parkinson's disease

Objective

To analyse postoperative pain due to osteoarthritis in patients with Parkinson's disease submitted to bilateral subthalamic nucleus stimulation.

Methods

Fifty-three parkinsonian patients (mean age, 59.9 ± 8.3 years; mean disease duration, 11.5 ± 4.2 years) referred for subthalamic nucleus stimulation were enrolled. Patients were prospectively asked to refer and describe any pain due to osteoarthritis they experienced at any time during the preoperative period and within the 6 postoperative months. Pre-existing pain due to osteoarthritis, therapeutic changes, parkinsonian motor disability and weight gain were assessed as explanatory factors for occurrence pain due to osteoarthritis after surgery.

Results

After surgery, thirty patients (57%) complained of pain due to osteoarthritis whereas all demonstrated great functional improvement. Twenty (67%) among the 30 experienced similar pain sensation before surgery. Symptoms occurred rapidly, between 4 and 26 postoperative weeks. Multiple stepwise regression analysis showed that pre-existing pain due to osteoarthritis, 6-month postoperative UPDRS III motor score and axial sub-score improvements in the off-drug/on-stimulation condition were accurate independent predictors of pain due to osteoarthritis after surgery (F(8, 41) = 2.20, p < 0.047).

Conclusion

Our results highlight the high prevalence of pain due to osteoarthritis arising shortly after subthalamic implantation. An accurate pain and osteo-articular assessment should be performed preoperatively in parkinsonian candidates for subthalamic nucleus stimulation in order to limit occurrence of complications in the early postoperative period.     

Lower tissue factor inhibition in patients with ST segment elevation than in patients with non ST elevation acute myocardial infarction

Introduction

Mechanisms to explain the different course of coronary thrombosis between ST elevation myocardial infarction (STEMI) and non-STEMI patients remain poorly defined. We hypothesize, however, that STEMI patients may present lower tissue factor plasma inhibition to partly account for their more persistent coronary thrombotic occlusion.

Materials and Methods

Total (t-TFPI ) and free tissue factor plasma inhibitor (f-TFPI), thrombin-antithrombin complex (TAT), plasminogen activator inhibitor 1 (PAI-1), von Willebrand factor (vWF), and fibrinogen were measured on admission and at 3 and 6 months in patients with a first STEMI (n:69) or non-STEMI (n:60). C reactive protein (CRP) was also measured on admission and at 3 months.

Results

STEMI patients showed lower admission levels of t-TFPI (p = 0.001), f-TFPI (p = 0.030) and fibrinogen (p = 0.022), and higher vWF levels (p = 0.005) than non-STEMI whereas TAT, PAI and CRP levels were comparable. At 3 and 6 months VWF, t-TFPI, f-TFPI, and TAT levels declined significantly in the 2 groups (p = 0.002) reaching similar values. CRP levels also declined at 3 months (p = 0.002). Moreover, the rate of cardiac mortality, non fatal MI or stroke during a 6 year follow-up were unrelated to admission coagulation parameters.

Conclusions

The lower inhibition of tissue factor and greater endothelial dysfunction in STEMI than in non-STEMI patients may enhance thrombosis at the culprit lesion and adjacent coronary plaques, and hence, account at least in part for their different pathophysiology. This condition, however, is limited to the acute phase.     

Certoparin versus UFH to prevent venous thromboembolic events in the very elderly patient: an analysis of the CERTIFY study

Introduction

There is an exponential rise of thromboembolic risk with age because of co-morbidities, immobility and pharmacotherapy. We aimed to investigate the benefits and risks of heparin prophylaxis in very elderly patients ≥ 80 years and the type of heparin used in a subgroup analysis of the CERTIFY trial.

Patients/methods

3,239 patients were randomized to 3,000 U aXa o.d. certoparin or 5,000 IU t.i.d. unfractionated heparin (UFH) for 8-20 days.

Results

Patients ≥ 80 years (n = 1,365) were more likely to be female, had a lower mean bodyweight, were more frequently using antiplatelets and had a GFR below 30 ml/min/1.73 m² more often than patients < 80 years (n = 1,875). The combined endpoint of proximal DVT, symptomatic non-fatal PE and VTE related death was experience by 5.26% of patients ≥ 80 years versus 3.51% in younger patients (OR 1.53; 95%CI 1.05-2.21; p = 0.03). There were no significant differences in both minor (OR 1.11; 95%CI 0.75-1.62) and major (OR 2.53; 95%CI 0.93-6.86) bleeding risks. Certoparin and UFH were equally effective in reducing thromboembolic risk in either age group. The risk of any (OR 0.45; 95%CI 0.26-0.79) and minor bleeding (OR 0.42; 95%CI 0.23-0.78) was reduced with certoparin in the very elderly only. There were more adverse events in elderly patients (OR 1.26; 95%CI 1.1-1.46), but rates were otherwise comparable.

Conclusions

The analysis confirmed the increased thromboembolic risk in very elderly patients, but demonstrated no increased bleeding risk. Certoparin and UFH were equally effective and safe with a reduced risk of minor bleeding complications with certoparin in the very elderly.     

Incidence and characteristics of asymptomatic distal deep vein thrombosis unexpectedly found at admission in an Internal Medicine setting

Introduction

Lower limb deep vein thrombosis (DVT) is the most frequent clinical manifestation of venous thromboembolism (VTE) and can involve proximal or distal veins. Distal DVT (dDVT) is often asymptomatic and data about its incidence and prognosis are scanty, especially in high risk medical inpatients. Therefore, no consensus exists on the value of detecting and treating dDVTs. Aim of study was to evaluate incidence and characteristics of asymptomatic isolated dDVT at admission in an Internal Medicine department.

Materials and methods

Consecutive patients hospitalized for acute medical illnesses, in whom VTE was not the admission diagnosis, underwent Doppler Ultrasonography. For all patients with dDVT standard treatment with therapeutic doses of low molecular weight heparin or fondaparinux was proposed. Follow-up visits were scheduled at 1, 6 and 12 weeks.

Results

One-hundred-fifty-four patients were enrolled. In 4.5% a proximal DVT and in 16.2% an asymptomatic dDVT were found. Female sex, elevated age and renal and electrolyte abnormalities were significantly associated to dDVT (p = 0.014, p = 0.009 and p = 0.046, respectively). Only low degree of mobility (LDM) was independently associated to dDVT [OR 7.97 (95%CI 2.42-26.27), p = 0.001)]. A high mortality rate, not for VTE-related causes, was found, especially in the first week, among dDVT patients.

Conclusions

We found a high incidence of clinically silent dDVTs. LDM evaluation could be useful to select patients at high risk in whom to perform a search for dDVT.     

Differences in the clinical course of heparin induced thrombocytopenia before and after the availability of HIT IgG class testing

Introduction

To determine whether the HIT IgG class platelet factor 4 (PF4) enzyme immunoabsorbant assay (EIA) influenced the duration of parenteral direct thrombin inhibitor (pDTI) therapy or bleeding risk in patients started on pDTI for a presumed diagnosis of HIT.

Materials/Methods

187 patients started on pDTI for presumed HIT were assessed in two time periods before (period 1, n = 88 patients) and after the introduction of an IgG-specific assay (period 2, n = 99 patients).

Results

Patients in period 2 were treated with pDTI therapy for a median of 5 days less (p < 0.0001) however the incidence of Grade III and IV bleeding episodes was not different. Bleeding was observed to occur early during the hospital course at a median of 2-3 days after initiation of the pDTI. The average pDTI drug acquisition cost was markedly decreased in period 2 when compared to period 1 (p < 0.0001).

Conclusions

Implementation of the IgG class HIT EIA resulted in a decrease in the number of days on a pDTI and a decrease in the average pDTI acquisition cost per patient without an observed change in serious bleeding events.     

Assessment of the performances of AcuStar HIT and the combination with heparin-induced multiple electrode aggregometry: A retrospective study

Background

Early diagnosis of immune heparin-induced thrombocytopenia (HIT) is challenging. HemosIL® AcuStar HIT and heparin-induced multiple electrode aggregometry (HIMEA) were recently proposed as rapid diagnostic methods.

Objectives

We conducted a study to assess performances of AcuStar HIT-IgG (PF4-H) and AcuStar HIT-Ab (PF4-H). The secondary objective was to compare the performances of the combination of Acustar HIT and HIMEA with standardised clinical diagnosis.

Methods

Sera of 104 suspected HIT patients were retrospectively tested with AcuStar HIT. HIMEA was performed on available sera (n = 81). The clinical diagnosis was established by analysing in a standardized manner the patient’s medical records. These tests were also compared with PF4-Enhanced®, LTA, and SRA in subsets of patients. Thresholds were determined using ROC curve analysis with clinical outcome as reference.

Results

Using the recommended thresholds (1.00 AU), the negative predictive value (NPV) of HIT-IgG and HIT-Ab were 100.0% (95% CI: 95.9%-100.0% and 95.7%-100.0%). The positive predictive value (PPV) were 64.3% (95% CI: 35.1%-87.2.2%) and 45.0% (95% CI: 23.2%-68.6%), respectively. Using our thresholds (HIT-IgG: 2.89 AU, HIT-Ab: 9.41 AU), NPV of HIT-IgG and HIT-Ab were 100.0% (95% CI: 96.0%-100.0% and 96.1%-100.0%). PPV were 75.0% (95% CI: 42.7%-94.5%) and 81.8% (95% CI: 48.3%-97.7%), respectively. Of the 79 patients with a medium-high pretest probability score, 67 were negative using HIT-IgG (PF4-H) test at our thresholds. HIMEA was performed on HIT-IgG positive patients. Using this combination, only one patient on 79 was incorrectly diagnosed.

Conclusion

Acustar HIT showed good performances to exclude the diagnosis of HIT. Combination with HIMEA improves PPV.