The von Willebrand factor Tyr2561 allele is a gain-of-function variant and a risk factor for early myocardial infarction.

The frequent von Willebrand factor (VWF) variant p.Phe2561Tyr is located within the C4 domain, which also harbors the platelet GPIIb/IIIa-binding RGD sequence. To investigate its potential effect on hemostasis, we genotyped 865 patients with coronary artery disease (CAD), 915 with myocardial infarction (MI), and 417 control patients (Ludwigshafen Risk and Cardiovascular Health Study) and performed functional studies of this variant. A univariate analysis of male and female carriers of the Tyr2561 allele aged 55 years or younger revealed an elevated risk for repeated MI (odds ratio, 2.53; 95% confidence interval [CI], 1.07-5.98). The odds ratio was even higher in females aged 55 years or younger, at a value of 5.93 (95% CI, 1.12-31.24). Cone and plate aggregometry showed that compared with Phe2561, Tyr2561 was associated with increased platelet aggregate size both in probands' blood and with the recombinant variants. Microfluidic assays revealed that the critical shear rate for inducing aggregate formation was decreased to 50% by Tyr2561 compared with Phe2561. Differences in C-domain circular dichroism spectra resulting from Tyr2561 suggest an increased shear sensitivity of VWF as a result of altered association of the C domains that disrupts the normal dimer interface. In summary, our data emphasize the functional effect of the VWF C4 domain for VWF-mediated platelet aggregation in a shear-dependent manner and provide the first evidence that a functional variant of VWF plays a role in arterial thromboembolism.

Hereditary risk factors for thrombophilia and probability of venous thromboembolism during pregnancy and the puerperium.

Venous thromboembolism (VTE) is a leading cause of maternal mortality. Few studies have evaluated the individual risk of gestational VTE associated with heritable thrombophilia, and current recommendations for antenatal thromboprophylaxis in women with severe thrombophilia such as homozygous factor V Leiden mutation (FVL) depend on a positive family history of VTE. To better stratify thromboprophylaxis in pregnancy, we aimed to estimate the individual probability (absolute risk) of gestational VTE associated with thrombophilia and to see whether these risk factors are independent of a family history of VTE in first-degree relatives. We studied 243 women with the first VTE during pregnancy and the puerperium and 243 age-matched normal women. Baseline incidence of VTE of 1:483 pregnancies in women ≥35 years and 1:741 deliveries in women <35 years was assumed, according to a recent population-based study. In women ≥35 years (<35 years), the individual probability of gestational VTE was as follows: 0.7% (0.5%) for heterozygous FVL; 3.4% (2.2%) for homozygous FVL; 0.6% (0.4%) for heterozygous prothrombin G20210A; 8.2% (5.5%) for compound heterozygotes for FVL and prothrombin G20210A; 9.0% (6.1%) for antithrombin deficiency; 1.1% (0.7%) for protein C deficiency; and 1.0% (0.7%) for protein S deficiency. These results were independent of a positive family history of VTE. We provide evidence that unselected women with these thrombophilias have an increased risk of gestational VTE independent of a positive family history of VTE. In contrast to current guidelines, these data suggest that women with high-risk thrombophilia should be considered for antenatal thromboprophylaxis regardless of family history of VTE.

Sex hormones and venous thromboembolism - from contraception to hormone replacement therapy.

The use of sex hormones such as combined oral contraceptives (COC) or hormone replacement therapy (HRT) increases the risk for venous thromboembolism (VTE) considerably, especially in patients with an increased intrinsic risk for thromboembolic complications. Despite public and media attention and increasing scientific evidence, prescription patterns seem to be hard to change. It is well recognized that the patient's baseline risk is the most relevant factor in the absolute risk for developing VTE. The relative risk increase associated with sex hormones, depends on the type and dosage of hormones, the route of application (oral, vaginal, transdermal), and for COC, on the specific combination of oestrogen and gestagen components. Consequently, a careful decision for or against any specific type of hormone treatment needs to be based on an assessment of the patient's risk profile (disposition) as well as on the treatment-associated risks and benefits (exposition). This review discusses the most common sex hormone treatments in contraception and HRT, the relevance for VTE risk patients, and strategies to counsel patients with regard to hormone use according to their risk profiles. Keywords: Oral contraceptives, hormonal contraception, hormone replacement therapy, venous thromboembolism.

The international, prospective Glanzmann Thrombasthenia Registry: treatment modalities and outcomes of non-surgical bleeding episodes in patients with Glanzmann thrombasthenia.

Standard treatment for Glanzmann thrombasthenia is platelet transfusion. Recombinant activated factor VII has been shown to be successful in patients with Glanzmann thrombasthenia with platelet antibodies or who are refractory to platelet transfusions. The Glanzmann Thrombasthenia Registry prospectively collected worldwide information on the effectiveness and safety of platelet transfusion, recombinant activated factor VII and/or antifibrinolytics for the treatment of bleeds in patients with Glanzmann thrombasthenia. Data relating to 829 non-surgical bleeding episodes were entered into the Glanzmann Thrombasthenia Registry (severe/moderate: 216/613; spontaneous/post-traumatic: 630/199). Recombinant activated factor VII alone was used in 124/829 bleeds, recombinant activated factor VII+antifibrinolytics in 107/829, platelets±antifibrinolytics in 312/829, antifibrinolytics alone in 219/829, and recombinant activated factor VII+platelets±antifibrinolytics in 67/829. The proportion of successful treatments to stop bleeding was 91.0% in cases treated with recombinant activated factor VII only, 82.7% for recombinant activated factor VII+antifibrinolytics, 72.7% for treatment with recombinant activated factor VII+platelets±antifibrinolytics, 78.8% for platelets±antifibrinolytics and 84.7% for antifibrinolytics alone. Treatment failure was documented in 18 bleeding events (2% of the total treatments), the majority of which were in patients receiving treatment with antifibrinolytics; bleeding re-started in 6% of bleeds after initial effective treatment. Thirty-five adverse events were reported, none of which was a thromboembolic event. Among treatments that included recombinant activated factor VII, only one patient reported three possibly drug-related non-serious adverse events (nausea, dyspnea and headache). To conclude, non-surgical bleeds were common and often severe in Glanzmann thrombasthenia; both platelets and recombinant activated factor VII appeared to be effective, and with good safety profiles, for the treatment of non-surgical bleeds. This trial was registered at clinicaltrials.gov identifier: NCT01476423.

The international, prospective Glanzmann Thrombasthenia Registry: treatment and outcomes in surgical intervention.

Standard treatment for Glanzmann thrombasthenia, a severe inherited bleeding disorder, is platelet transfusion. Recombinant factor VIIa is reported to be effective in Glanzmann thrombasthenia with platelet antibodies and/or refractoriness to platelet transfusions. We aimed to evaluate recombinant factor VIIa effectiveness and safety for the treatment and prevention of surgical bleeding in patients, with or without platelet antibodies and/or refractoriness, using data from the Glanzmann Thrombasthenia Registry, an international, multicenter, observational, post-marketing study of rFVIIa. Between 2007 and 2011, 96 patients were treated for 206 surgical procedures (minor 169, major 37). History of platelet antibodies was present in 43 patients, refractoriness in 23, antibodies+refractoriness in 17, while 47 had no confirmed antibodies/refractoriness. Treatments analyzed included antifibrinolytics, recombinant factor VIIa, recombinant factor VIIa+antifibrinolytics, platelets±antifibrinolytics and recombinant factor VIIa+platelets±antifibrinolytics. The most frequent treatment for minor procedures was recombinant factor VIIa+antifibrinolytics (n=65), and for major procedures, recombinant factor VIIa+platelets±antifibrinolytics (n=13). In patients without antibodies/refractoriness, recombinant factor VIIa, either alone or with antifibrinolytics, and platelets±antifibrinolytics were rated 100% effective for minor and major procedures. The effectiveness of treatment for minor procedures in patients with antibodies and refractoriness was 88.9% for recombinant factor VIIa, 100% for recombinant factor VIIa+antifibrinolytics, 66.7% for platelets±antifibrinolytics and 100% for recombinant factor VIIa+platelets±antifibrinolytics. One of four adverse events reported for surgery was considered recombinant factor VIIa-treatment-related (non-fatal thromboembolic event in an adult female receiving recombinant factor VIIa+platelets+antifibrinolytics). For all patients, regardless of platelet antibody or refractoriness status, recombinant factor VIIa, administered with or without platelets (±antifibrinolytics), provided effective hemostasis with a low frequency of adverse events in surgical procedures in Glanzmann thrombasthenia patients. This trial was registered at clinicaltrials.gov identifier: 01476423.

A single nucleotide polymorphism determines protein isoform production of the human c-FLIP protein.

The cellular FLICE-inhibitory protein (c-FLIP) is a modulator of death receptor-mediated apoptosis and plays a major role in T- and B-cell homeostasis. Three different isoforms have been described on the protein level, including the long form c-FLIP(L) as well as 2 short forms, c-FLIP(S) and the recently identified c-FLIP(R). The mechanisms controlling c-FLIP isoform production are largely unknown. Here, we identified by sequence comparison in several mammals that c-FLIP(R) and not the widely studied c-FLIP(S) is the evolutionary ancestral short c-FLIP protein. Unexpectedly, the decision for production of either c-FLIP(S) or c-FLIP(R) in humans is defined by a single nucleotide polymorphism in a 3' splice site of the c-FLIP gene (rs10190751A/G). Whereas an intact splice site directs production of c-FLIP(S), the splice-dead variant causes production of c-FLIP(R). Interestingly, due to differences in protein translation rates, higher amounts of c-FLIP(S) protein compared with c-FLIP(R) are produced. Investigation of diverse human cell lines points to an increased frequency of c-FLIP(R) in transformed B-cell lines. A comparison of 183 patients with follicular lymphoma and 233 population controls revealed an increased lymphoma risk associated with the rs10190751 A genotype causing c-FLIP(R) expression.

No evidence for increased intraoperative bleeding in aortic-valve stenosis: a comparative analysis of haemotherapy in 136 patients undergoing aortic-valve replacement.

OBJECTIVE: An association of aortic-valve stenosis and abnormal bleeding, particularly from gastrointestinal angiodysplasia, has been reported. In this setting, high-shear stress generated by the transvalvular gradient leads to a conformational change of plasmic von Willebrand factor, making this adhesive protein more susceptible for proteolytic cleavage. Consequently, highest-molecular weight multimers of the von Willebrand factor are degraded through a von Willebrand factor specific protease leading to impaired platelet-related haemostasis. METHODS AND RESULTS: To assess the role of aortic-valve stenosis as a factor predicting abnormal intraoperative bleeding in patients suffering from aortic-valve stenosis, we compared the number of intraoperatively administered blood components during aortic-valve replacement for aortic-valve stenosis (n = 50), aortic-valve insufficiency (n = 19) and combined aortic-valve defects (n = 67). As a result, the three subgroups did not differ significantly regarding the mean number of transfused red-blood cell units (0.94 +/- 1.36, 0.4 +/- 0.9, or 0.86 +/- 1.3, respectively) and plasma units (0.04 +/- 0.28, 0.21 +/- 0.71, or 0.15 +/- 0.61, respectively). None of the patients received platelet concentrates. A multivariate logistic regression model adjusted for age and gender did not show an influence of the presence and severity of aortic-valve stenosis on intraoperatively applied haemotherapy. CONCLUSION: Along with our findings, the presence or severity of aortic-valve stenosis does not predict an increased need for intraoperative transfusion of blood components. Thus, this cardiac defect does not seem to represent a major risk determinant for intraoperative bleeding despite the high prevalence of shear-stress induced von Willebrand factor abnormalities in this setting.

Causes, etiology and diagnosis of acquired von Willebrand disease: a prospective diagnostic workup to establish the most effective therapeutic strategies.

Acquired von Willebrand disease (aVWD) occurs in association with a variety of underlying disorders, most frequently in lymphoproliferative and myeloproliferative disorders, other malignancies, and cardiovascular disease. aVWD is a complex and heterogeneous defect with a multifactorial etiology and the pathophysiologic mechanisms remain unclear in many cases. Assays for anti-factor VIII (FVIII)/von Willebrand factor (VWF) activities often yield negative results although antibodies may be present in autoimmune disease and some lymphoproliferative disorders. Functional assays of VWF in patients' plasma and particularly in heart valve disease, VWF multimer analysis are important for aVWD diagnosis. In patients with normal partial thromboplastin times and normal VWF activity, the diagnosis of aVWD is based on clinical suspicion and a careful bleeding history, which should prompt the clinician to initiate further laboratory investigations. Management of bleeding in aVWD relies mainly on desmopressin, FVIII/VWF concentrates and high-dose intravenous immunoglobulin. The half-life of VWF may be very short, and in bleeding episodes high doses of FVIII/VWF concentrates at short intervals may be necessary even when high-dose intravenous immunoglobulin was applied before. Since the optimal treatment strategy has not yet been defined for aVWD of different etiology, controlled multicenter trials aiming at the development of standardized treatment protocols are urgently needed.

Successful use of danaparoid in two pregnant women with heart valve prosthesis and heparin-induced thrombocytopenia Type II (HIT).

Anticoagulant therapy with heparin for the prevention of thromboembolism in pregnant women with prosthetic heart valves is associated with an increased risk to the mother and/or the fetus. A life-threatening complication of the therapy with heparin is heparin-induced thrombocytopenia type II (HIT). danaparoid has not yet been reported to be safe and effective for this indication. This study reports on a 26-year-old woman with tricuspidal valve prosthesis and a 37-year-old woman with a St. Jude Medical mitral valve prosthesis who were anticoagulated with danaparoid during pregnancy because of HIT. Anti-Xa levels were between 0.6 and 1.2 IU/mL during pregnancy with target levels of 1.0 IU/mL. Cesarean section was performed at anti-Xa levels of 0.3 and 0.7 IU/mL. One woman developed a placental hematoma at the 32nd week of gestation, which did not increase over the following week. Both patients delivered healthy boys. Heparin-induced thrombocytopenia in pregnant women with prosthetic heart valve can be successfully managed with danaparoid.

Use of recombinant factor VIIa in inherited and acquired von Willebrand disease.

Recombinant factor VIIa (rFVIIa) is increasingly used outside the labeled indications for the treatment of life-threatening bleeding episodes after failure of respective standard therapy. In this article, the authors focus on the use of the agent in patients with inherited or acquired von Willebrand disease (vWD). Although the current experience is sparse, published cases indicate the high efficacy of rFVIIa for the treatment of patients refractory to conventional treatment. The agent may be used in patients with congenital vWD complicated by alloantibodies directed against substituted von Willebrand factor or in the presence of concomitant hemostatic defects as well as acquired vWD with hitherto limited therapeutic options. Controlled clinical studies are necessary to define the use of rFVIIa in this clinical setting.

The homozygous leu variant of the factor XIII Val34Leu polymorphism as a risk factor for the manifestation of thrombotic microangiopathies.

The 34 Leu (100T) variant of the factor XIII Val34Leu (G100T-) polymorphism slows down fibrinolysis and has been proposed as a thrombotic risk factor. In this pilot study, we enrolled 40 patients (mean age +/- SD = 38 +/- 11 years) and 728 controls to assess the role of this genetic variant for the manifestation of thrombotic microangiopathies. From the genotype prevalences, an increased manifestation risk for carriers of the TT genotype (homozygous Leu variant) of the factor XIII Val34Leu (G100T-) polymorphism was calculated (odds ratio [OR] = 2.44; 95% confidence interval [CI] = 0.8-7.6; P = .11). This association was statistically significant for patients with thrombotic thrombocytopenic purpura-hemolytic-uremic syndrome (TTP-HUS) (OR = 6.6; 95% CI = 1.7-25.9; P = .006). Our data suggest a role of the homozygous Leu variant of the factor XIII Val34Leu polymorphism in the manifestation of thrombotic microangiopathies. Decreased fibrinolysis in the presence of this genetic variant provides a plausible explanation for this association.

Are prothrombotic variants of platelet glycoprotein receptor polymorphisms involved in the pathogenesis of thrombotic microangiopathies?

Thrombotic microangiopathies are life-threatening disorders characterized by vascular microthromboses, schistocytic hemolytic anemia, and thrombocytopenia. Although recent research has partially explained the pathogenesis of these rare entities, the determinants contributing to the onset and modulating the severity of thrombotic microangiopathies are largely unknown. The present study assessed the putative role of prothrombotic platelet receptor polymorphisms in thrombotic microangiopathies that have been found to be associated with premature onset of myocardial infarction in predisposed individuals. Thirty-four consecutive patients admitted with the diagnosis of thrombotic microangiopathy and 759 healthy subjects were enrolled. Genotyping of the human platelet antigen (HPA) 2 an the Kozak sequence polymorphism of GP Ibalpha of the platelets' von Willebrand factor receptor glycoprotein (GP) Ib-V-IX, the HPA-1 and the HPA-3 polymorphism of the fibrinogen receptor GP IIb-IIIa (integrin alpha(IIb)beta( 3)) and the HPA-5 and GP Ia 807 C/T polymorphism of the collagen receptor GP Ia-IIa (integrin alpha(2)beta(1)) were determined according to standard procedures. As a result, no significant differences in the prevalence of prothrombotic variants of platelet-receptor polymorphisms between patients and healthy control subjects were observed. However, although not significant, the prothrombotic bb genotype of the HPA-1 polymorphism was more prevalent in the patients. The findings do not provide evidence that platelet receptor polymorphisms are determinants for the onset of thrombotic microangiopathies or predispose to a more severe course. Along with this observation, screening for respective platelet-receptor polymorphisms does not appear to contribute to risk stratification of affected patients.

The TT genotype of the C677T polymorphism in the methylentetrahydrofolate reductase as a risk factor in thrombotic microangiopathies: results from a pilot study.

In this study, we assessed the potential role of the TT genotype of the gene of the methylenetetrahydrofolate reductase for the manifestation of thrombotic microangiopathies, enrolling 40 affected patients (mean age [+/- standard deviation] 35 +/- 11 years). As a result, the methylenetetrahydrofolate reductase 677TT genotype was more prevalent in patients with thrombotic microangiopathies compared with controls (adjusted odds ratio = 2.58, 95% confidence interval = 1.2-5.7, P = .018), particularly in those suffering from the hemolytic uremic syndrome. A hemolytic more severe clinical course of thrombotic microangiopathies in carriers of the methylenetetrahydrofolate reductase 677TT genotype was not observed. In summary, our findings suggest a significant influence of the methylenetetrahydrofolate reductase genotype on the manifestation of thrombotic microangiopathies. The 677 TT genotype of this polymorphism appears to be a risk factor for manifestation of these rare thrombotic disorders, possibly explained by endothelial activation and increased oxidative stress.

The G1691A mutation of the factor V gene (factor V Leiden) and the G20210A mutation of the prothrombin gene as risk factors in thrombotic microangiopathies.

Factor V Leiden (FVL) mutation and prothrombin G20210A mutation are common hereditary risk factors for venous thrombosis. In the current study, 40 patients (mean age +/- standard deviation, 35 +/- 11 years) and 764 healthy control subjects (mean age +/- standard deviation, 37 +/- 14 years) were enrolled to assess the potential role of these mutations in the manifestation of thrombotic microangiopathies. Compared with controls, neither the heterozygous FVL mutation (7.5% vs 8.5%; P = 1) nor the heterozygous prothrombin mutation (2.5% vs 2.8%; P = 1) was more prevalent in the patients. The findings do not support a significant role of FVL and prothrombin mutations as risk factors for the manifestation of thrombotic microangiopathies. Thus, screening for these mutations does not allow the identification of individuals at increased risk for these rare thrombotic disorders.

The International Prospective Glanzmann Thrombasthenia Registry: Pediatric Treatment and Outcomes.

Background Standard treatment for Glanzmann thrombasthenia (GT), a severe inherited bleeding disorder, is platelet transfusion. Recombinant activated factor VII (rFVIIa) is reported to be effective in GT with platelet antibodies and/or refractoriness to platelet transfusions. Methods We evaluated rFVIIa effectiveness and safety for the treatment and prevention of surgical and nonsurgical bleeding in children <18 years old, with or without platelet antibodies and/or refractoriness, as reported in the GT Registry (GTR). Data were used from the GTR, an international, multicenter, observational, postmarketing study of rFVIIa that prospectively collected data on the treatment and outcomes of bleeds in patients with GT. Only patients with a diagnosis of congenital GT were included in the registry. Results Between 2007 and 2011, 27 children were treated for 44 surgical procedures (minor: 36; major: 8); nonsurgical bleeds occurred in 104 patients (599 episodes: severe, 145; moderate, 454; spontaneous, 423; posttraumatic, 176). The effectiveness of treatment for minor procedures, major procedures, nonsurgical bleeds was 6/6, 1/1, and 75/84 for rFVIIa, 6/6, 2/2, and 64/76 for rFVIIa + antifibrinolytics (AF), 11/12, 1/1, and 162/214 for platelets ± AF, and 5/6, 0/3, and 33/45 for rFVIIa + platelets ± AF. In all, 25 adverse events were reported in children; no thromboembolic events were reported. Conclusion For all patients, regardless of platelet antibody or refractoriness status, rFVIIa, administered with or without platelets (± AF), provided effective hemostasis with a low frequency of adverse events in surgical, as well as nonsurgical, bleeding in patients with GT. clinicaltrials.gov identifier: NCT01476423.

Haplotype-specific expression of the human PDGFRA gene correlates with the risk of glioblastomas.

Aberrant expression of the platelet-derived growth factor alpha-receptor (PDGFRA) gene has been associated with various diseases, including neural tube defects and gliomas. We have previously identified 5 distinct haplotypes for the PDGFRA promoter region, designated H1, H2alpha, H2beta, H2gamma and H2delta. Of these haplotypes H1 and H2alpha are the most common, whereby H1 drives low and H2alpha high transcriptional activity in transient transfection assays. Here we have investigated the role of these PDGFRA promoter haplotypes in gliomagenesis at both the genetic and cellular level. In a case-control study on 71 glioblastoma patients, we observed a clear underrepresentation of H1 alleles, with pH1 = 0.141 in patients and pH1 = 0.211 in a combined Western European control group (n = 998, p < 0.05). Furthermore, in 3 out of 4 available H1/H2alpha heterozygous human glioblastoma cell lines, H1-derived mRNA levels were more than 10-fold lower than from H2alpha, resulting at least in part from haplotype-specific epigenetic differences such as DNA methylation and histone acetylation. Together, these results indicate that PDGFRA promoter haplotypes may predispose to gliomas. We propose a model in which PDGFRA is upregulated in a haplotype-specific manner during neural stem cell differentiation, which affects the pool size of cells that can later undergo gliomagenesis.

Celiac artery thrombosis in a young patient with multiple platelet receptor polymorphisms and local compression syndrome.

Numerous clinical and experimental studies have been published concerning platelet receptor polymorphism and their role in causing myocardial infarction at an earlier age. It is still unclear, however, whether these polymorphisms are a risk factor for other occlusive diseases such as those in visceral arteries. We report a case of a young woman with acute celiac artery thrombosis and multiple platelet receptor polymorphisms. In addition, the intraoperative exploration showed some evidence of a local vascular compression syndrome. The patient was successfully treated with a bypass procedure and combined anticoagulation. It seems that platelet receptor polymorphisms are a moderate risk factor for local artery thrombosis regardless of vascular region. The obligatory precondition is pre-existing vascular damage, such as that caused by a local compression syndrome.

Recombinant factor VIIa for the prophylaxis of perioperative hemorrhage in a patient with congenital factor XI deficiency undergoing brain tumor neurosurgery.

The authors report on the first successful use of recombinant activated factor VII for the prophylaxis of bleeding during brain tumor neurosurgery in a patient suffering from inherited factor XI deficiency. Using the agent, surgery was performed without any bleeding complications. In this setting, off-label use of recombinant activated factor VII appears to be a promising alternative for patients suffering from this rare hemostatic defect with hitherto limited therapeutic options.

Venous thromboembolism prophylaxis in acutely ill hospitalized medical patients: findings from the International Medical Prevention Registry on Venous Thromboembolism.

BACKGROUND: Evidence-based guidelines recommend that acutely ill hospitalized medical patients who are at risk of venous thromboembolism (VTE) should receive prophylaxis. Our aim was to characterize the clinical practices for VTE prophylaxis in acutely ill hospitalized medical patients enrolled in the International Medical Prevention Registry on Venous Thromboembolism (IMPROVE). METHODS: IMPROVE is an ongoing, multinational, observational study. Participating hospitals enroll the first 10 consecutive eligible acutely ill medical patients each month. Patient management is determined by the treating physicians. An analysis of data on VTE prophylaxis practices is presented. RESULTS: From July 2002 to September 30, 2006, 15,156 patients were enrolled from 52 hospitals in 12 countries, of whom 50% received in-hospital pharmacologic and/or mechanical VTE prophylaxis. In the United States and other participating countries, 52% and 43% of patients, respectively, should have received prophylaxis according to guideline recommendations from the American College of Chest Physicians (ACCP). Only approximately 60% of patients who either met the ACCP criteria for requiring prophylaxis or were eligible for enrollment in randomized clinical trials that have shown the benefits of pharmacologic prophylaxis actually received prophylaxis. Practices varied considerably. Intermittent pneumatic compression was the most common form of medical prophylaxis utilized in the United States, although it was used very rarely in other countries (22% vs 0.2%, respectively). Unfractionated heparin was the most frequent pharmacologic approach used in the United States (21% of patients), with low-molecular-weight heparin used most frequently in other participating countries (40%). There was also variable use of elastic stockings in the United States and other participating countries (3% vs 7%, respectively). CONCLUSIONS: Our data suggest that physicians' practices for providing VTE prophylaxis to acutely ill hospitalized medical patients are suboptimal and highlight the need for improved implementation of existing evidence-based guidelines in hospitals.